Tropical Pacific Observing Needs to Advance Process Understanding and Representation in Models Workshop

US CLIVAR (Climate Variability and Predictability Program)

A workshop to gather community input on Tropical Pacific Observing needs to advance our understanding of multi-scale ocean-atmosphere coupled processes and to discuss how such observations could help improve satellite retrievals, data assimilation, and climate, forecast, and biogeochemical models.

More info: https://usclivar.org/meetings/tpon-2021

Filter displayed posters (177 keywords)

ENSO (4) MJO (3) Saildrone (3) ENSO prediction (2) El Nino (2) TIW (2) Tropical Instability Waves (2) air-sea fluxes (2) buoys (2) diurnal cycle (2) double ITCZ (2) fluxes (2) fronts (2) precipitation (2) saildrone (2) salinity (2) sea surface salinity (2) surface fluxes (2) turbulence (2) show more... Acidification (1) Air-Sea Interaction (1) Air-sea flux (1) Algal (1) Aqua Biodiversity (1) Atmospheric boundary layer (1) Atmospheric chemistry (1) Barotropic Response (1) COARE (1) CRM (1) CYGNSS satellite (1) Central Pacific (1) Climate Change (1) Cloud Life Cycle (1) Cold Pool (1) Coupled Data Assimilation (1) Data Assimilation (1) Double ITCZ bias (1) ECCO (1) ECMWF OSE experiment (1) ENSO precursors (1) ENSO prediction and predictability (1) Easterly waves (1) Eastern Pacific (1) El Niño onset (1) Equatorial Kelvin Wave (1) Eutrophication (1) Fresh equatorial jets (1) ITCZ (1) Indian Summer Monsoon Extreme (1) Interannual Variability (1) Intraseasonal Oscillations (1) Isotopes (1) LES (1) Latent heat bias (1) Meridional heat transport (1) Mesoscale air-sea fluxes (1) Mesoscale cold pools (1) Mesoscale convection (1) Modeling (1) Multiscale processes (1) Ocean Reanalysis (1) Ocean-atmosphere interaction (1) Oceanic Mixed Layer (1) Oxygen cycle (1) PDO (1) PUMP (1) Pacific Meridional Overturning Circulation (1) Pollution (1) Precipitation (1) Prediction (1) Rainfall (1) SST-precipitation relationship (1) Satellite observations (1) Seasonal Prediction (1) Sub-seasonal wind forcing (1) Subsurface Observations (1) Sunda Strait (1) Surface fluxes (1) TAO/TRITON Buoys (1) TPOS2020 (1) Tropical East Pacific Observing System (TPOS) (1) Tropical Pacific Observing System; data assimilation; OSSE (1) Tropical convection (1) UAS (1) USV (1) Upwelling (1) UxS (1) air-sea (1) air-sea interaction (1) air-sea interactions (1) atmosphere (1) autonomous sampling (1) barrier layer (1) biogenic gas transfer (1) boundary layer (1) buoy (1) climate model (1) climate models (1) co2 (1) coastal upwelling (1) cold pools (1) cold tongue (1) cold tongue SST (1) coupled instability (1) coupled model errors (1) dataset (1) diurnal warm layers (1) drone (1) equatorial rainfall (1) extreme weather (1) global climatology (1) h2o (1) heat flux (1) heatwaves (1) human well-being (1) humidity sensors (1) in-situ observations (1) infrared (1) interannual variability (1) intraseasonal timescale (1) maritime continent (1) mixing (1) model (1) model bias (1) modeling (1) momentum (1) momentum flux (1) observations (1) ocean atmosphere exchange (1) ocean current (1) ocean forecasts (1) ocean models (1) ocean reanalysis (1) ocean stability (1) ocean turbulence (1) ocean wind observing system (1) ocean-atmosphere interaction (1) paleoclimate (1) process understanding (1) rain (1) rainfall (1) remote sensing (1) representation error (1) salinity assimilation (1) satellite (1) satellite observation (1) scale interactions (1) sea surface temperature (1) seawater (1) skin temperature (1) sst (1) stable layers (1) stable oxygen isotope (1) storm tracking (1) strong wind event (1) submesoscale (1) subseasonal forecast (1) subsurface ocean structure (1) surface air humidity and temperature (1) surface currents (1) surface meteorology (1) surface observations (1) surface wind convergence (1) thermodynamics (1) transport (1) tropical Pacific (1) tropical rainfall (1) urban greenspaces (1) variability (1) vertical velocity (1) warm water volume (1) water isotopes (1) water mass transformation (1) waves (1) western Pacific Ocean (1) wind stress (1) winds (1)

Show Posters: with Video Chat with Recorded Presentation

Tracks

1. Multi-scale Ocean-Atmopshere Coupled Processes (12)

2. Earth System Prediction (9)

3. Atmospheric Studies and Observing Needs (12)

4. Ocean Studies and Observing Needs (12)

5. OSSEs, Data Assimilation, Reanalyses (7)

6. Observing the Ocean-Atmosphere Transition Zone (11)

▼ 1. Multi-scale Ocean-Atmopshere Coupled Processes Back to top

Butterfly: revealing the oceans’ influence on our weather and climate

Chelle Gentemann, Carol Anne Clayson, Tony Lee, Shannon Brown, Aneesh Subramanian, Aneesh Subramanian, Mark Bourassa, Hyodae Seo, Kelly Lombardo, Sarah Gille, Tom Farrar, Rhys Parfitt, Brian Argrow

Abstract

Presented by

Aneesh Subramanian

Institution

University of Colorado Boulder

Keywords

Satellite observations, Mesoscale air-sea fluxes

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Available Poster sessions all days

Impacts of Precipitation-Evaporation-Salinity Coupling on Upper Ocean Stratification and Momentum Over the Tropical Pacific Prior to Onset of the 2018 El Niño

Shuyi S. Chen and Brandon W. Kerns

Abstract

Presented by

Shuyi Chen

Institution

University of Washington, Department of Atmospheric Sciences

Keywords

Air-Sea Interaction, MJO, El Nino

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Available Monday May 24, 2021, 15:10-16:10 EDT

On the Rapid Ocean Response to High-Frequency Intense Rainfall

Xiaolin Zhang1 and Allan J. Clarke2

Abstract

Intense rain in the deep tropics can exceed 1 cm in 10 minutes or 7 cm in one day. Analytical results for the ocean response to spatially uniform rainfall over a circular region yield physical insight about how the size of the ocean response depends on the rainfall rate, its duration, and its horizontal scale. Since the extra mass of the freshwater flux is felt throughout the water column, the initial ocean response is barotropic and the ocean adjusts via long gravity waves propagating at a speed c equal to about 200 m/s. A crucial parameter is , the ratio of the time a/c it takes the wave to cross the rainfall spatial scale a compared to the time scale of the forcing. Analysis using the IMERG precipitation data set shows that even in the intense rainfall of the western Pacific South Pacific Convergence Zone (SPCZ) and the eastern Pacific Intertropical Convergence Zone (ITCZ) the rainfall scales are such that the ocean sea level response is only a few mm. Examination of the rainfall intensity suggests that the initial sea level response to surface mixing of the rainfall is also small.

Presented by

Xiaolin Zhang

Institution

1. University of Hamburg, 2. Florida State University

Keywords

Rainfall, Barotropic Response, western Pacific Ocean, ITCZ

Eutrophication and Acidification problems of the Black Sea

Dr. Kakha NADIRADZE, Mrs. Nana PHIROSMANASHVILI, Ms. Mariam GOGINASHVILI, Ms. Tekla NADIRADZE

Abstract

Climate Change, Overfishing, Pollution, Rising atmospheric carbon dioxide (CO 2 levels, from fossil fuel combustion and deforestation, along with agriculture and land-use practices are causing wholesale increases in Black Sea water CO 2 and inorganic carbon levels. The field studies have shown that Black Sea Marine environments are in conjunction with other climate change-related factors like droughts torrential rains and flooding, severe storms, heavy snow, abnormal temperatures, etc also due to the increased river and soil pollution, contamination by microplastics and chemical substances atmospheric pollution particulates suspended in the atmosphere and chemical substances and blooming of Algal. The Black Sea, a nearly enclosed and isolated environment has suffered from severe ecological changes during the last three decades The acidification and eutrophication are the results of pollution of coastal waters by nutrients is a result of Food production ( animal operations and aquaculture), and Farmers sometimes are the main contributors to the growing number of polluting the Black Sea Coastal Waters Urbanization of Rural Areas, increasing sewage discharges and runoff from agriculture and populated lands.

Presented by

Dr. Kakha Nadiradze <nadiradzekakha@gmail.com>

Institution

AFRD Georgia

Keywords

Aqua Biodiversity, Pollution, Climate Change, Eutrophication, Acidification, Algal

How influential is the MJO on ENSO development?

Antonietta Capotondi

Abstract

Wind variations at sub-seasonal (20-90 days) timescales, associated with the Madden Julian Oscillation (MJO) have been viewed as key players in the initiation of ENSO events through the excitation of oceanic Kelvin waves in the same frequency range. In this study, we make use of satellite-based daily wind observations, as well as daily sea surface temperature (SST) and sea surface height (SSH) data from satellite retrievals, to assess the role of sub-seasonal wind variations on ENSO initiation and evolution. Our results indicate that although MJO-related winds do excite sub-seasonal Kelvin waves, their influence on tropical thermocline variations is very small compared to the signal associated with interannual Kelvin waves. Our study further shows that while sub-seasonal variability was somewhat smaller during the weak El Nino event of 2014 relative to the extreme 1997-98 El Nino, the main reason of the failed development of the 2014 event was the lack of a significant wind response at interannual timescales, in stark contrast to what happened during the 1997-98 event. These results are relevant to the understanding of the role of scale interactions, or lack of, in tropical Pacific interannual variability and to a more informed assessment of the quantities and scales that need to be observed. More information at: https://doi.org/10.1175/JCLI-D-17-0842.1

Presented by

Antonietta Capotondi

Institution

University of Colorado/CIRES and NOAA/PSL

Keywords

Sub-seasonal wind forcing, interannual variability

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Available May 24, 3-4 pm EDT, or at other times arranged via email

Equatorial Pacific sea surface temperature is one of the drivers of tropical Pacific double ITCZ bias in climate models

Dhrubajyoti Samanta, Kristopher B. Karnauskas, Nathalie F. Goodkin, & Benjamin P. Horton

Abstract

Global coupled climate models are used for climate change predictions. However, these climate models are imperfect due to internal biases. One of the major biases that has persisted across multiple generations of climate models is the double Intertropical Convergence Zone (ITCZ) in the tropical Pacific. The double ITCZ is characterized as a nearly symmetric bimodal, annual precipitation pattern straddling the equator. Because of the strong relationship between sea surface temperature (SST) and convection in the tropics, precipitation biases are sensitive to the background SST behaviours. Using the historical simulations (1861-2005) of 24 coupled climate models from Coupled Model Intercomparison Project Phase 5 (CMIP5) and an atmospheric general circulation model, we demonstrate that a cold equatorial Pacific SST bias exacerbates the double ITCZ bias in the Pacific, which highlights a few potentially faulty processes in the coupled climate models. We further hypothesize that the representation of the Equatorial Undercurrent (EUC) has a strong relationship with cold equatorial Pacific SST bias and is dependent on the horizontal resolution of the ocean component of the coupled climate models. Examining CMIP6 climate models with varying horizontal resolution, we further found that a reduction in the double ITCZ bias may be feasible with improved representation of the EUC and reduction of the cold SST bias in the eastern equatorial Pacific.

Reference:

Samanta, D., Karnauskas, K. B., & Goodkin, N. F. (2019). Tropical Pacific SST and ITCZ biases in climate models: Double trouble for future rainfall projections? Geophysical Research Letters, 46(4), 2242–2252. https://doi.org/10.1029/2018GL081363

Presented by

Dhrubajyoti Samanta <dhruba@ntu.edu.sg>

Institution

Nanyang Technological University, Singapore

Keywords

Double ITCZ bias, climate model, cold tongue SST, tropical Pacific

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Available 24 April 3.10 PM to 4.10 PM EDT (i.e., 25 April 3.10 AM to 4.10 AM Singapore) , & at other time arranged via email

Equatorial convection between Boreal Winter Monsoon with MJO and the interaction of Indo-Western Pacific Ocean over Maritime Continent

Khafid Rizki Pratama

Abstract

The relationship between Winter Monsoon (WM) and Madden Julian Oscillation (MJO) is an essential factor in the anomaly of rainfall that occurs on the surface during the development of the Indo-Asian Monsoon (IAM) onset on the Maritime Continent. The investigation used synoptic observation data, model datasets, and re-analysis data. The WM phase was significantly more robust in the addition of rainfall in the Maritime Continent than during the active IAM. Walker circulation affected the convective modulation in the Western region due to the Indo-West Pacific Ocean (IWPO) interaction. Besides, WM thermodynamics in MJO-WM inhibited Borneo Vortex's growth but influenced the updraft activity of multi-cell clouds. The method was carried out by classifying convective frequencies in Western Indonesia to the WM propagation during active IAM and MJO and ocean-atmosphere stratification on a diurnal cycle during the DJF and MAM periods of 2016 - 2018. This research supports the components of the International Years of Maritime Continent (YMC) Program in Indonesia for multi-scale interactions associated with the spread of atmospheric convection. MJO and WM's interaction can be seen in the TRMM data, where the diurnal convective pattern is balanced to the afternoon-morning rainfall. The ECMWF model with a resolution of 0.25 x 0.25 showed a strong wind during IAM onset. The ocean stratification pattern from RAMA subsurface profile affected by Indonesia Throughflow (ITF) with anomalous values of 0.3 - 0.5 degrees Celsius and the mixing layer depth is below 50 meters. This study's results are expected to become a reference in predicting and monitoring the onset of the winter monsoon and rainfall in Indonesia.

Presented by

Khafid Rizki Pratama

Institution

Indonesia Agency for Meteorology Climatology and Geophysics, Meteorology Department Bandung Institute of Technology, Graduate Student of Oceanography

Keywords

Ocean-atmosphere interaction, maritime continent, equatorial rainfall

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Available May 24th 3:10pm - 4pm EDT

Diurnal Cycle of Tropical Oceanic Mesoscale Cold Pools in Observations and High Resolution Model

Piyush Garg1*, Stephen W. Nesbitt1, Timothy J. Lang2, George Priftis3

Abstract

Tropical convection is dominated by regimes ranging from deep organized to shallow convective systems. Mesoscale processes such as cold pools within tropical convective systems can play a significant role in the evolution of convection over land and open ocean. Although cold pools are widely observed, their diurnal properties are not well understood over tropical oceans and land. The oceanic cold pool identification metric here is based on the gradient feature (GF) technique and is compared with diurnally-resolved buoy-identified thermal cold pools. This study provides a first-ever diurnal climatology of GF number, area, and attributed TRMM 3B42 precipitation using a space-borne scatterometer (RapidScat). Buoy data over the Pacific, Atlantic, and Indian Ocean have been used to validate and examine the RapidScat-identified diurnal cycle of GF number and precipitation. Buoy-observed cold pool duration, precipitation, temperature, and wind speed is analyzed to understand the in situ cold pool properties over tropical oceans. GF- and buoy-observed cold pool number and precipitation exhibits a similar bimodal diurnal variability with a morning and afternoon maxima, thus establishing confidence in using GF as a proxy to observe cold pools over tropical oceans. NASA globally-merged (MERGIR) infrared brightness temperature (TB) and ERA5 reanalysis' total column water vapor (TCWV) is then used to obtain a conceptual understanding of the bimodal diurnal behavior of tropical oceanic mesoscale cold pools.

Once an observational perspective of tropical oceanic mesoscale cold pool diurnal cycle is obtained, Icosahedral Nonhydrostatic (ICON) model, which is a global high-resolution (2.5 km) cloud resolving model (CRM) from Dynamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) initiative, is used to identify thermal cold pools using virtual temperature anomaly. The model ran from 00 UTC 1 Aug to 23 UTC 10 Aug 2016 using ECMWF initial and boundary conditions. ICON-simulated thermal cold pool climatology for 40-days permitted the synoptic and mesoscale circulations and matched physically with scatterometer-derived GF climatology. Diurnal cycle of ICON-simulated cold pool properties is compared against RapidScat-observed GF and GPM IMERG precipitation diurnal cycle. ICON cold pool and IMERG precipitation miss the secondary afternoon peak in convective activity while successfully observing dominant morning peak corresponding to deep convection.

Presented by

Piyush Garg <pgarg7@illinois.edu>

Institution

1*Department of Atmospheric Sciences, University of Illinois Urbana-Champaign; 2 NASA Marshall Space Flight Center, AL; 3 University of Alabama-Huntsville, AL

Keywords

Mesoscale cold pools, satellite, buoys, diurnal cycle, CRM

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Available Monday, April 24th 2021: 15:10 - 16:20 EDT or an appointment set up via email

Cloud Feedback Biases Influence Model Projections of Extreme El Nino

Samantha Stevenson (1), Andrew Wittenberg (2), John Fasullo (3), Sloan Coats (4), Bette Otto-Bliesner (3)

Abstract

The majority of future projections in the Coupled Model Intercomparison Project (CMIP5) show more frequent exceedances of the 5 mm/day rainfall threshold in the eastern equatorial Pacific rainfall during El Niño, previously described in the literature as an increase in ‘‘extreme El Niño events’’; however, these exceedance frequencies vary widely across models, and in some projections actually decrease. Here we combine single-model large ensemble simulations with phase 5 of the Coupled Model Intercomparison Project (CMIP5) to diagnose the mechanisms for these differences. The sensitivity of precipitation to local SST anomalies increases consistently across CMIP-class models, tending to amplify extreme El Niño occurrence; however, changes to the magnitude of ENSO-related SST variability can drastically influence the results, indicating that understanding changes to SST variability remains imperative. Future El Niño rainfall intensifies most in models with 1) larger historical cold SST biases in the central equatorial Pacific, which inhibit future increases in local convective cloud shading, enabling more local warming; and 2) smaller historical warm SST biases in the far eastern equatorial Pacific, which enhance future reductions in stratus cloud, enabling more local warming. These competing mechanisms complicate efforts to determine whether CMIP5 models under- or overestimate the future impacts of climate change on El Niño rainfall and its global impacts. This relation between present-day model biases and future projections highlights the critical need for improved observations of air-sea fluxes in the equatorial Pacific.

Presented by

Samantha Stevenson

Institution

University of California, Santa Barbara; (2) NOAA Geophysical Fluid Dynamics Laboratory; (3) National Center for Atmospheric Research; (4) University of Hawaii at Manoa

Keywords

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Available May 24th 3:10pm - 4pm EDT

Surface air humidity from autonomous observing systems

Simon de Szoeke, J. Tom Farrar, Steve Jayne

Abstract

Accurate in situ surface humidity measurements are essential to improving our knowledge of the global distribution of ocean surface heat fluxes, coupled climate, and atmosphere-ocean interactions. Ocean surface evaporation is a major and variable component of the ocean heat budget and hydrologic cycle. Water vapor is the atmosphere’s the source for precipitation and its strongest and most variable greenhouse gas. Latent heating and radiative feedbacks modulate seasonal to subseasonal weather. Small errors in air surface temperature and humidity in models and reanalysis contribute large air-sea flux errors, demonstrating the requirement for accurate surface humidity measurements.

Autonomous satellite and in situ observing systems have emerging capabilities to measure near-surface air temperature and humidity. Present satellite retrievals of surface air temperature and humidity are less accurate than satellite sea surface temperature retrievals. Near-surface humidity retrievals can be improved by sensing radiances at more wavelengths. Developing these retrievals will require in situ surface observations.

Humidity is difficult to measure in marine surface weather. About 150 moored buoy stations, mostly on the equator and western boundary current regions measure surface fluxes accurately. Global ocean evaporation monitoring requires an order of magnitude more observations. Robust sensors deployed in situ on drifting and remotely piloted autonomous platforms; such as surface floats and profiling floats and gliders, Saildrones, and Wave Gliders; could provide these observations at lower cost than moorings. A submersible humidity sensor for Argo floats is proposed that would observe surface air temperature, humidity, and estimate fluxes above contemporaneous ocean profile observations. Uncrewed and diving floats can safely measure near extreme weather conditions such as tropical cyclones.

Presented by

Simon de Szoeke

Institution

Oregon State University

Keywords

humidity sensors, surface air humidity and temperature, autonomous sampling

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Available May 25 3:05pm-4:05pm EDT

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Multiscale Processes in MJO-induced Warm Pool Eastward Extension and the Onset of 2018 El Niño

Yakelyn R. Jauregui and Shuyi S. Chen

Abstract

The El Niño–Southern Oscillation (ENSO) prediction, especially the timing of the onset of El Niño, is a grand challenge. Better understand the observed evolution of the equatorial Pacific warm pool and coupled atmosphere-ocean processes during El Niño onset is fundamental to the ENSO prediction. The warm pool eastward extension (WPEE) is often associated with strong and/or consecutive Madden-Julian Oscillation (MJO) events as shown in Jauregui and Chen (2021), which may serve as a “trigger” to the El Niño onset. However, the mechanism(s) responsible for the MJO-ENSO interaction is not well understood. This study aims to better understand the physical processes by which the MJO induces WPEE leading to El Niño onset.

To capture the structure and evolution of multiscale processes over the western-central tropical Pacific warm pool region, this study focuses on a time period that the MJO events and onset of El Nino were observed across a broad range of temporal and spatial scales. We use satellite and in situ observations to describe how consecutive MJO events, which occurred in January-May 2018, influenced the onset of El Niño in August 2018. Observations include TRMM-GPM rainfall, CCMP surface winds, OISST, SMAP surface salinity, and in situ measurements from moorings and ARGO floats. A relatively high-resolution coupled atmosphere-ocean model simulation is used to better understand the physical processes associated with the MJO-induced WPEE. The coupled model consists of WRF with 12-km of horizontal resolution and 45 vertical levels and HYCOM with 1/12 degree and 42 levels (Kerns and Chen 2021).

The coupled model simulation reproduces the observed MJO events and WPEE from January-August 2018. Analyses from the observations and model simulation provide physical insights into multiscale structure associated with the MJO-induced WPEE, from the mesoscale convective activity affecting the upper-ocean mixing and air-sea interaction processes to large-scale oceanic Kelvin waves and development of barrier layer as well the consequent zonal pressure gradient relaxation leading to the onset of El Niño across time scales from hours to months. The simulation shows that freshwater from precipitation during the MJO resulted in salinity changes, leading to the formation and maintenance of barrier layers, which affect air-sea interaction processes and favors the upper ocean stratification that maintained higher SSTs at the onset of El Niño. We describe how the coupled system evolves from La Niña to the onset of the El Niño, with a focus on the warm pool eastern edge during the transition.

Presented by

Yakelyn Ramos Jauregui

Institution

University of Washington

Keywords

MJO, Fresh equatorial jets, ENSO, El Niño onset, Multiscale processes

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Available May 24th 3:10 - 4.10 PM EDT

Review of Tropical East Pacific Air-Sea Interface, Ocean and Atmospheric Parameter Spread in Observations, Reanalyses and Coupled Models

Yolande L. Serra and Boris DeWitte

Abstract

The tropical East Pacific (EPAC) is highlighted in the TPOS 2020 2nd Report as being exceptionally problematic for decades in terms of both process understanding and inadequacy of representation in climate models. The TPOS 2020 EPAC Task Team aimed to identify opportunities for addressing some of the gaps in knowledge within the EPAC through 1) exploitation of existing data sets, 2) identification of targeted observations to address key processes, and 3) development of a regional ocean reanalyses to assist in the design of an optimal observing system for the region. Over the last five years progress in each of these areas proved difficult. The key processes the Task Team identified within the EPAC involve many complex systems and time scales making it difficult to design an effective process study. In addition, obtaining funding for a regional ocean reanalysis project aimed at aiding the design of a process study is challenging in a region with limited resources and inhomogeneous data sharing policies. Despite these challenges, the EPAC remains an important component of TPOS and continued input from the community on how best to observe its key processes and constrain coupled models within the region is needed. This presentation is meant to keep the conversation about the EPAC moving forward. We will review the current status of model spread in parameters associated with the coupled mean state (e.g., double ITCZ) and in El Niño Southern Oscillation anomalies. We will also highlight TPOS 2020 recommendations aimed at reducing some of the model spread in the EPAC and upcoming process studies testing new observing technologies in the region. Finally, we solicit feedback on how to continue to close the gap on model errors and improve representation and monitoring of the EPAC going forward.

Presented by

Yolande Serra

Institution

CICOES, University of Washington, Seattle, WA, USA

Keywords

Tropical East Pacific Observing System (TPOS), cold tongue, double ITCZ, coastal upwelling, coupled model errors

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Available May 24, 3:10 to 4:00 PM EDT

▼ 2. Earth System Prediction Back to top

Satellite Study of Correlation of Climate Variability with Air-Sea CO2 exchange to develop Pacific Sea-Level Variability Numerical Forecasting Models (PSLV-NFM) Over Tropical Pacific Oceanic Regions

Dr. Virendra Goswami

Abstract

Presented by

Virendra Goswami

Institution

Keywords

Mesoscale Controls on the Equatorial Pacific O2 Balance

Yassir A. Eddebbar (SIO), A. Subramanian (CU Boulder), D. Whitt (NASA), A. Verdy (SIO) M. Mazloff (SIO), M. Long (NCAR), M. Merrifield (SIO)

Abstract

Presented by

Yassir Eddebbar

Institution

Scripps Institution of Oceanography, UC San Diego

Keywords

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Available May 24-Wed 26 3-4PM EDT

An overview of iodine chemistry over the Indian and Southern Ocean waters using ship-based observations and modelling

Anoop Mahajan, Swaleha Inamdar, Liselotte Tinel, Qinyi Li, Alba Badia, Alfonso Saiz-Lopez, Kirpa Ram, Rosie Chance, Lucy Carpenter

Abstract

In this study, we present an overview of observations and modelling of reactive iodine chemistry in the marine boundary layers of the Indian and Southern Ocean. Ship observations of iodine oxide (IO) from 2015 to 2017 show its ubiquitous presence with values up to 1 pptv (parts per trillion) in this region. In order to identify the source of iodine in this region, we computed inorganic fluxes of iodine using tropospheric ozone (O3), sea surface iodide concentration, and wind speed. The estimated fluxes of hypoiodous acid (HOI) and elemental iodine (I2) did not adequately explain the observed IO levels in the Indian and Southern Ocean region. However, a significant correlation of IO with chlorophyll-a indicates a possible biogenic control on iodine chemistry in the Indian Ocean marine boundary layer (MBL). To understand the role of organic and inorganic precursors in MBL iodine chemistry, we used the Weather Research and Forecast model coupled with Chemistry (WRF-Chem version 3.7.1) incorporating halogen (Br, Cl, and I) chemistry. Results from the modelling study show that only organic sources of iodine underestimate the detected IO in the northern Indian Ocean MBL. This highlights the importance of inorganic emissions as a source of iodine over the ocean. However, the inorganic flux emissions in the model had to be reduced by 40% to match the detected IO levels in this region. The reduced emission produces an overall good match between the observed and modelled IO levels . This discrepancy with flux emissions in both the model study and observation highlights that there may be uncertainties in the estimation of the fluxes or that they do not perform well for the Indian and Southern Ocean region. The results show that inclusion of iodine chemistry causes significant regional changes to O3 (up to 25%), nitrogen oxides (up to 50%), and hydroxyl radicals (up to 15%) affecting the chemical composition of open ocean MBL and coastal regions of the Indian sub-continent. Thus it is crucial to include iodine chemistry in atmospheric models and to estimate its impact on the MBL chemical composition accurately. Accurate estimation of iodine precursors in the MBL calls for an urgent need to improve the existing parameterisation of inorganic fluxes and direct measurements of the HOI and I2 may prove useful in the accurate quantification of iodine precursors in the marine atmosphere.

Presented by

Anoop Mahajan

Institution

Indian Institute of Tropical Meteorology

Keywords

Atmospheric chemistry, ocean atmosphere exchange

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Available May 24th, 15:00 - 16:00 EDT

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Multiyear Statistical Prediction of ENSO Enhanced by the Tropical Pacific Observing System

Desislava Petrova, Joan Ballester, Siem Jan Koopman, Xavier Rodó

Abstract

The theoretical predictability limit of El Niño–Southern Oscillation is in the range of several of years, but long-lead predictions of El Niño (EN) and La Niña (LN) are only sporadically reported in the literature. Operational forecasting schemes usually do not predict beyond the spring predictability barrier. Recent efforts have been dedicated to the improvement of dynamical models, while statistical schemes still need to take full advantage of the availability of ocean subsurface variables, provided regularly for the last few decades as a result of the Tropical Ocean–Global Atmosphere Program (TOGA). Here we use a number of predictor variables, including temperature at different depths and regions of the equatorial ocean, in a flexible statistical dynamic components model to make long-lead retrospective predictions (hindcasts) of the Niño-3.4 index in the period 1970–2016. The major EN episodes are successfully predicted up to 2.5 years in advance, including the recent extreme 2015/16 EN. The analysis suggests that events are predicted more accurately after the completion of the observational array in the tropical Pacific in 1994, as a result of the improved data quality and coverage achieved by TOGA.

Presented by

Desislava Petrova

Institution

Climate and Health Program, Barcelona Institute for Global Health

Keywords

ENSO, Prediction, Subsurface Observations

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Available May 24th 15 - 16 EDT

Leveraging seawater δ18O values to extract paleosalinity information from coral δ18O records (zoom pw 068399)

Jessica L. Conroy1,2, Diane M. Thompson3, Kristine L. DeLong4, Samantha Stevenson5, Bronwen Konecky6, Nicole K. Murray1, Emilie P. Dassié7, Judson Partin8

Abstract

Stable oxygen isotopic ratios (δ18O) in marine bio-carbonates are commonly utilized to reconstruct past ocean and coupled ocean-atmosphere variability on timescales beyond the reach of instrumental observations, which are spatially and temporally limited in the tropical Pacific. These measurements provide constraints on past seawater temperature, due to the thermodynamics of isotope fractionation, but also past seawater salinity, as both salinity and the δ18O value of seawater are similarly impacted by evaporation, advection, and other hydrological processes. Here we use coral δ18O records from the new PAGES Iso2k database to assess the potential of coral δ18O values to provide information on past salinity variations. Annual pseudocoral simulations indicate that in the western tropical Pacific, a substantial fraction of coral δ18O variance is derived from seawater δ18O values, which covary strongly with salinity. In agreement with this variance decomposition, we find that many coral δ18O time series from the western tropical Pacific are significantly correlated with mid to late 20th century salinity. However, variations in the linear slope of the seawater δ18O-salinity relationship have a substantial influence on the strength of the salinity signal inferred from coral δ18O values. To date, seawater δ18O measurements remain extremely limited worldwide and especially in the tropical Pacific. This key variable and its relationship with salinity, which is also poorly observed, is thus inadequately constrained in time and space, with insufficient observations to assess the stability of the δ18O-salinity relationship across the tropical oceans. A coordinated network of seawater δ18O observations is vital to continue the critical work of understanding the relationship between ocean chemistry and hydroclimate, as well as reconstructing past climate from marine bio-carbonates.

Presented by

Jessica Conroy <jconro@illinois.edu>

Institution

1Department of Geology, University of Illinois Urbana-Champaign, Champaign, IL 2Department of Plant Biology, University of Illinois Urbana-Champaign, Champaign, IL 3Department of Geosciences, The University of Arizona, Tucson, AZ, 4 Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA, Bren School of Environmental Science and Management, 5University of California, Santa Barbara CA, 6 Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 7Univ. Bordeaux, CNRS, EPOC, EPHE, UMR 5805, F-33600 Pessac, France 8Institute for Geophysics, University of Texas at Austin, Austin TX

Keywords

stable oxygen isotope, seawater, salinity

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Available May 24, 15:10-16:10 EDT

Water Isotope Observations as Dynamical Bridge from the Past to the Future

Kim M. Cobb, David Noone, Adriana Bailey, Samantha Stevenson, Gabe Bowen, Jess Conroy, Jesse Nusbaumer, Sylvia Dee, Rice Alyssa Atwood, Bronwen Konecky, Allegra Legrande, Natalie Burls, Ricardo Sanchez, Naoyuki Kurita, Valerie Masson Delmotte, Nerilie Abram, Kei Yoshimura, Camille Risi, Martin Werner

Abstract

Models and data are consistent with anthropogenic influence on the tropical Pacific climate system across a range of timescales, with profound implications for the predictability of tropical Pacific climate variability and its regional impacts. One of the most robust signals of anthropogenic influence concerns shifts in the large-scale hydrological cycle in the tropical Pacific that point to ongoing changes in the mean state of tropical Pacific as well as changes in the hydrological impacts of phenomena such as the El Nino-Southern Oscillation. At the same time, there are profound uncertainties associated with key processes and feedbacks governing the evolution of interannual to decadal-scale variability in the tropical Pacific, and how they may evolve under continued anthropogenic forcing. As physical tracers that integrate key processes in the atmosphere, in the ocean, and across the ocean-atmosphere interface, hydrogen and oxygen isotope ratios of water provide a powerful tool to detect subtle changes in the water cycle, and diagnose the key processes that drive regional- to global-scale hydrological trends and variability. New observing technology unlocks the potential to routinely measure this physical tracer via ship-based platforms, remote sensing, and autonomous platforms, as a key component of future observing systems. Such observations can be directly compared to water isotope tracers incorporated into many earth system models that simulate ocean-atmosphere processes of high dynamical interest. The tropical Pacific represents a particularly rich target for such observations, given the wealth of climate information derived from natural isotope-based signals obtained from paleoclimate archives that augment and extend the short, sparse instrumental climate record in this key region. In this presentation, the US CLIVAR Working Group on Water Isotopes presents the outcomes of a recent community workshop as they relate to the design of future tropical Pacific observing systems. In particular, we demonstrate specific strategies for enhancing the value of traditional physical oceanographic and meteorological observations through the addition of water isotope observations within the hierarchy of investments in coordinated observing platforms.

Presented by

Kim Cobb

Institution

US CLIVAR Water Isotope Working Group

Keywords

ENSO, water isotopes, paleoclimate, PDO, salinity, modeling, observations, TPOS2020

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Available May 25th, 3-4pm EDT

Importance of Moored Buoy Observations towards Monsoon Prediction: A Case Study

Maheswar Pradhan, Ankur Srivastava, Suryachandra A. Rao, Deep Sankar Banerjee, Abhisek Chatterjee, P. A. Francis, O. P. Sreejith, M. Das Gupta & V. S. Prasad

Abstract

Increased frequency of El-Niño and droughts over India in the recent decade and the severity of their impact make the seasonal prediction an inherent component of mitigation and preparedness. A lot of effort is dedicated to improving the seasonal prediction of extreme events by improving dynamical models’ physics, resolution, and quality, and coverage of observing networks. The predictability at seasonal time scales comes mainly from the ocean, and hence the dynamical models’ capability relies on the quality of the ocean initial conditions. The prior studies have verified the sensitivity of ocean initial conditions to observations collected from various platforms, including Argos, moored buoys, expendable bathythermographs, etc. The impact of moored buoys on the ocean analysis and the sea surface temperature forecast skill has also been studied earlier. What remains unaddressed is the contribution of moored buoy observations towards the seasonal monsoon prediction. In the present study, the sensitivity of rainfall prediction over India to moored buoy observations has been tested through a couple of sensitivity experiments. The absence of tropical moored buoy observations results in large errors in ocean initial conditions that force a La-Niña type pattern over the central equatorial Pacific and modulates the monsoon rainfall to be above normal rainfall in the predictions. But the inclusion of missing observations reduces the biases in initial conditions, which subdued the La-Niña like conditions and resulted in below normal rainfall prediction. Hence moored buoys are found to be critical in order to produce quality ocean initial conditions and accurate seasonal forecast of monsoon over India.

Presented by

Maheswar Pradhan

Institution

Indian Institute of Tropical Meteorology, Pune

Keywords

TAO/TRITON Buoys, Indian Summer Monsoon Extreme, Seasonal Prediction

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Available May 24 , 15.10-16.10 PM EDT

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Improving paleo hydroclimate reconstructions with observations of δ18Osw

Sara Sanchez, PAGES Coral Hydro2k

Abstract

Climate models suggest that the hydrological cycle will feature some of the most robust responses to climate change, yet many regional nuances remain uncertain. These trends may be already observable but are difficult to discern due to the sparse network of precipitation and sea surface salinity (SSS) observations, particularly over the tropical oceans. Surface coral archives have been used extensively to examine past climate variability in the data sparse tropical oceans. Paired analysis of coral skeletal δ18O and Sr/Ca allow for paleo reconstructions of δ18O of seawater, a variable that is primarily controlled by the processes of precipitation, evaporation, and ocean circulation, similar to SSS. Analysis of reconstructions of δ18O of seawater from coral archives in conjunction with the developing fields of isotope enabled modeling and paleoclimate data assimilation provide unprecedented opportunity to assess tropical hydroclimate variability prior to the satellite era. The PAGES Coral Hydro2k network is building a robust network of archives of coral δ18O and Sr/Ca to best facilitate this model-data intercomparison. However, this potentially powerful evaluation of past hydroclimate variability from the coral archives cannot be fully utilized at present. The deficient of instrumental observations of δ18Osw inhibits rigorous quality control checks of individual coral archives, prevents the assessment of the realism in isotope enabled models, and hinders the optimization of proxy system models and thus reconstruction skill in paleo-data assimilation reconstructions. There is a lot of low-hanging fruit in paleoclimate (and modern climate) research if only more observations of δ18Osw were available. Enhancing observation systems for δ18Osw would benefit many working groups.

Presented by

Sara Sanchez

Institution

Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder

Keywords

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Available 3:10pm EDT on May 24th

Sensitivity of asymmetric Oxygen Minimum Zones to mixing intensity and biological processes in the tropical Pacific: a model

Xiujun Wang1,2, Kai Wang1, Raghu Murtugudde2, Dongxiao Zhang3

Abstract

The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, models have difficulties in reproducing the observed asymmetric OMZs in the tropical Pacific. Here, we apply a fully coupled basin-scale model to evaluate the impacts of intensity of vertical mixing and various biological processes on the dynamics of OMZs in the tropical Pacific. We first utilize observational data of dissolved oxygen (DO), dissolved organic nitrogen (DON) and oxygen consumption rate to calibrate and validate the basin-scale model. Our model experiments show that while enhanced vertical mixing can lead to some improvements in the simulation of mid-depth DO, implementation of varying rate of DON remineralization and stoichiometry can significantly improve the model capability of reproducing the asymmetric OMZs. We find that DO is more sensitive to biological processes in the upper OMZs but to physical processes in the lower OMZs. Our analyses demonstrate that the dynamics of dissolved organic matter (DOM) plays a larger role in regulating the asymmetric OMZs in the tropical Pacific. Integrative observational studies of DOM stoichiometry in the whole water column are needed to better understand the oxygen cycle in the middle ocean.

Presented by

Xiujun Wang

Institution

1College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China 2Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20740, USA 3JISAO, University of Washington and NOAA, Seattle, Washington 98115, USA

Keywords

Oxygen cycle, model

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Available May 24th, 3:15-4:15pm EDT

▼ 3. Atmospheric Studies and Observing Needs Back to top

Heatwaves risks and modeling the potential of urban greenspaces in Karachi city

Adnan Arshad1,2, Ristina Siti Sundari3, Huma Qamar4, Muhammad Ashraf5 , Shabnam Pourshirazi6

Abstract

The global surface temperature increase by the end of the 21st century is expected to exceed 1.5 °C relative to the 1850-1900 period for most scenarios, and is likely to exceed 2.0 °C for many scenarios. The average surface temperature of this region has increased at a rate of 0.25 °C per decade over the past 50 years. Karachi is the largest city of Pakistan, and at seventh worldwide, highly vulnerable to extreme weather events predominantly continues heatwaves (HWs) periods. Our studies projected that the annual mean air temperature of the city with one million residents could be 1-3°C hotter than its nearby surroundings. Long-term exposure to peak temperature (°C) followed by maximum humidity (%) has a fatal effect on health, and it increases risk of morbidity and death rate. There is a substantial decrease in urban greenspaces and intensification in build-up areas of the city during 1984–2016. Urban greenspaces can reduce the ambient temperature of cities by 1°C, thus dropping the urban heat island and improve air quality index (AQI). SILVA-model projected that two-thirds (19%) of the city's carbon emission could be deposited by mangrove forest (MF).

Available via email or WhatsApp for questions. (+923330621790)

Presented by

Adnan Arshad <ad@cau.edu.cn>

Institution

1,2,China Agricultural University Beijing, China; 2PODA Organization; 3University of Perjuangan; 4Ayub Agricultural Research Institute; 5University of Baluchistan; 6Gorgan University of Agricultural Sciences and Natural Resources

Keywords

extreme weather, heatwaves, urban greenspaces, human well-being

A Different Look at the Double ITCZ Problem

Chidong Zhang

Abstract

The conventional perception of the double ITCZ (dITCZ) Problem is: Measured by precipitation, a dITCZ over the tropical eastern Pacific exists in observations only during boreal spring, but in numerical models it is commonly exaggerated and erroneously extended into the other seasons. An alternative perception of the dITCZ problem is proposed as: Measured by surface wind convergence, a dITCZ over the tropical eastern Pacific exists in observations in almost all seasons, but in numerical models it is erroneously transformed into a dITCZ in precipitation.

Presented by

Chidong Zhang

Institution

NOAA PMEL

Keywords

surface wind convergence, double ITCZ

In situ observations of the near-shore atmospheric boundary layer during ATOMIC/EUREC4A from small Uncrewed Aircraft Systems

Gijs de Boer, Janet Intrieri, Radiance Calmer, Steve Borenstein, Christopher Choate, Michael Rhodes, Jonathan Hamilton, Christopher Cox, Brian Argrow, Christopher Fairall

Abstract

During the 2020 Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) and ElUcidating the Role of Cloud- Circulation Coupling in ClimAte (EUREC4A) field campaigns, a team from the University of Colorado Boulder deployed the RAAVEN Remotely-Piloted Aircraft System (RPAS). The RAAVEN RPAS was equipped with the miniFlux measurement system to observe the marine boundary layer upwind of Morgan Lewis, Barbados. Over the course of 23 days, the team completed 39 flights covering nearly 80 flight hours. Flights were conducted in and just above the sub-cloud mixed layer at altitudes between 10 and 1000 m, with a focus on capturing regular thermodynamic and kinematic profiles of the lower atmosphere, along with statistics on vertical transport and spatial variability. In this presentation, we will give initial details on the observed state of the lower atmosphere. This includes information on the structure and internal variability of thermodynamic and kinematic properties, turbulence intensity, turbulent surface fluxes and their variability, and details on the structure of vertical velocities in the lower atmosphere.

Available via the Slack workspace or through email at gijs.deboer@colorado.edu

Presented by

Gijs de Boer <gijs.deboer@colorado.edu>

Institution

University of Colorado Boulder, NOAA Physical Sciences Laboratory

Keywords

Atmospheric boundary layer, drone, UAS, fluxes, turbulence, thermodynamics, vertical velocity

Easterly wave contributions to seasonal rainfall over the tropical Americas in observations and a regional climate model

Christian Dominguez, James Done and Cindy Bruyere

Abstract

Easterly waves (EWs) are important moisture carriers and their variability can impact the total May–November rainfall, defined as seasonal precipitation, over the Tropical Americas. The contribution of EWs to the seasonal precipitation is explored over the tropical Americas using rain gauge stations, reanalysis data and a regional model ensemble during the 1980–2013 period. In the present study, EWs are found to produce up to 50% of seasonal rainfall mainly over the north of South America and contribute substantially to interannual regional rainfall variability. An observational analysis shows that the El Niño Southern Oscillation (ENSO) affects EW frequency and therefore, their contribution to seasonal rainfall. In recent years, tropical cyclone (TC) activity over the Main Development Region (MDR) of the tropical North Atlantic has a negative impact on regional seasonal precipitation over northern South America. High TC activity over MDR corresponds to below-normal precipitation because it reduces the EW activity reaching northern South America through the recurving of TC tracks. Recurving TC tracks redirect moisture away from the tropical belt and into the mid-latitudes. However, this relationship only holds under neutral ENSO conditions and the positive phase of the Atlantic Multidecadal Oscillation. A 10-member regional model multi-physics ensemble simulation for the period 1990–2000 was analyzed to show the relationships are robust to different representations of physical processes. This new understanding of seasonal rainfall over the tropical Americas may support improved regional seasonal and climate outlooks.

Presented by

Christian Dominguez

Institution

National Autonomous University of Mexico (UNAM)

Keywords

Easterly waves, tropical rainfall

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Available May 25th, 3-4 pm (US EDT)

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Boundary layer scale interaction in the ITCZ: The role of convective cold pools

Eric Skyllingstad, Simon de Szoeke, Carol Anne Clayson, James Edson

Abstract

Cloud resolving simulations of an idealized intertropical convergence zone (ITCZ) are used to examine how convective cold pools interact in defining the position and width of active convection. Experiments are conducted with a mixed layer ocean having a zonal band of sea-surface temperature 3 degrees above the background temperature at a latitude of 12o N. The model develops a convergent circulation with easterly trade winds north of the warm band and a region of convection north of the SST center. The width of the convection expands and eventually balances the steady inflow circulation because of surface cold pool outflow. The resulting region of convection is relatively steady with large-scale wave activity resembling barotropic instability. Sensitivity experiments are performed with reduced cold pools by turning off rain evaporative cooling. In both cases, the meridional width of ITCZ convection is greatly reduced, leading to a narrow band structure. Our results suggest that nonlocal effects of convective cold pools are critical for convective clusters such as found in the ITCZ and are needed for accurate cumulus parameterization. Measurements of the tropical boundary layer variability produced by convection is a key element in designing these future parameterizations.

Presented by

Eric Skyllingstad <eric.skyllingstad@oregonstate.edu>

Institution

Oregon State University and Woods Hole Oceanographic Institute

Keywords

Tropical convection, cold pools

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Available May 25, 2021 1 15:00-16:00 EDT

A new dataset of rainfall isotopes on the island of O'ahu

Giuseppe Torri, Alison Nugent, Fayçal Lamroui, Zhiming Kuang, Brian Popp

Abstract

Water isotopes have been widely used to study the climate system, with applications ranging from paleoclimatology to groundwater hydrology. In the tropical Pacific, water isotopes have been analyzed, for example, to diagnose the profile of atmospheric large-scale vertical velocity or to track changes in the strength of the Walker circulation. In spite of their potential to quantify or constraint many physical processes that are relevant for the climate system, observations of water isotopes in the tropical Pacific remain relatively scarce. Here, a new dataset is introduced which consists of weekly rainfall data collected from different locations across the island of Oʻahu, Hawaiʻi. Analysis of the samples provides insight into the orographic effect on the isotopic composition of rainfall on tropical islands, as well as on the isotopic signature of various weather patterns that affect the Hawaiian Islands. In addition, two case studies that are representative of the dry and wet season weather, a trade wind shower and a Kona storm, respectively, are discussed in detail using an isotope-enabled model. The weekly observational isotopic rainfall samples are compared with the numerical simulation case studies, and the physical mechanisms that cause the two precipitation systems to have different isotopic signatures are discussed.

Presented by

Giuseppe Torri

Institution

University of Hawaii

Keywords

Isotopes, rainfall, dataset

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Available May 25th, 15:05 EDT

Accurate measurements of surface fluxes to constrain climate model processes

H Annamalai

Abstract

Within the realism of limited direct observations over the tropical oceans, understanding and quantifying processes that determine precipitation is challenging. Specifically, during ENSO evolution surface latent heat flux anomalies along the central-eastern equatorial Pacific are a major contributor to near-surface moist static energy (MSE) anomalies that subsequently determine anomalous moisture availability in the atmospheric boundary layer. Focusing on ENSO-related precipitation anomalies, detailed process-oriented diagnostics (POD) based on MSE analysis is applied to CMIP-era model. Both in coupled and uncoupled solutions, the large diversity in the model simulated boundary layer moisture anomalies is readily attributed to similar diversity in the simulated surface turbulent fluxes. To assess robustness in model errors, the model results are validated against multiple reanalysis products that introduces another level of “uncertainty”. Furthermore, POD reveals that during both El Nino and La Nina winters boundary layer moisture anomalies imprint on column relative humidity anomalies that determine simulated precipitation anomalies themselves. It is therefore argued that accurate measurements of surface turbulent fluxes that eventually imprint on the atmospheric boundary-layer moisture content with subsequent impact on the triggering of atmospheric convection are needed to constrain near-surface and boundary layer processes in climate models.

Presented by

H Annamalai

Institution

International Pacific Research Center (IPRC), University of Hawaii

Keywords

Surface fluxes, climate models

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Available May 25 -26; 3.00-4.00 PM EDT

Evaluation of zonal surface wind anomalies by the Tropical Pacific surface wind observing system

Larry W. O’Neill, Carol Anne Clayson, J. Tom Farrar, Tony Lee, Shayne McGregor, and Susan Wijffels

Abstract

We identify a regime of significant disagreement between collocated satellite and buoy vector wind observations during westerly wind events (WWEs). WWEs are often associated with atmospheric convective events characterized by precipitation and sharply increased high frequency wind variance. These events are also implicated in initiation of changes in ENSO phase. During WWEs, zonal wind RMS differences between scatterometer and buoy wind observations are about 5 m/s for QuikSCAT and 3 m/s for ASCAT. For easterly wind regimes, the scat-buoy RMS zonal wind differences are about 1.0 m/s for both QuikSCAT and ASCAT. Our analysis indicates these zonal wind differences are due mainly to differences in wind direction between the scatterometers and buoys. While the analysis is ongoing, we present evidence showing that much of the disagreement is associated with two effects: (1) rain-induced uncertainties in satellite scatterometer winds; and (2) increased wind variability associated with tropical convective systems, which increases buoy-scatterometer wind differences due to mismatches between buoy point measurements and scatterometer areal-averaged measurements.

Presented by

Larry O'Neill

Institution

Oregon State University

Keywords

ocean wind observing system

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Available Tuesday, May 25, 12-1pm PDT (3-4 EDT)

Cold Pools Observed by Uncrewed Surface Vehicles in the Central and Eastern Tropical Pacific

Samantha M. Wills (1), Meghan F. Cronin (2), Dongxiao Zhang (1)

Abstract

New in-situ observations collected by Saildrones, a novel uncrewed surface vehicle, are used to investigate atmospheric cold pools during three six-month missions to the central and eastern (140W – 125W) tropical Pacific. Cold pool fronts in the atmospheric boundary layer are identified by a -1.5C air temperature drop occurring in 10 minutes or less. While cold pool events were observed in the central Pacific as far north as 30N and within the equatorial band, the majority of observed cold pools occurred within the convective, low-wind shear environment of the Intertropical Convergence Zone. Composite time series analysis of measurements during the 382 cold pool events reveals new insights on high-frequency variations in air and sea surface temperature, wind speed, humidity, pressure, and sea surface salinity associated with cold pool fronts. The results highlight the capabilities of new autonomous platforms to resolve smaller spatial and temporal scales of variability over observationally-sparse ocean regions.

Presented by

Samantha Wills <samantha.m.wills@noaa.gov>

Institution

1. University of Washington, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, 2. NOAA Pacific Marine Environmental Laboratory

Keywords

Saildrone, Cold Pool, Eastern Pacific, Central Pacific, surface observations

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Available May 25, 2021 15:05 - 16:05 EDT

The Relationship between Tropical Precipitation and Precipitable Water in CMIP6 Simulations and Implications for Observations

Samson M. Hagos, Ruby Leung, Oluwayemi A. Garuba, Jian Lu, Bryce Harrop, Min-Seop Ahn and Charlotte Demott

Abstract

It is well documented that over the tropical oceans, column-integrated precipitable water (pw) and precipitation (P) have a nonlinear relationship. In this study moisture budget analysis is used to examine this P–pw relationship in a normalized precipitable water framework. It is shown that the parameters of the nonlinear relationship depend on the vertical structure of moisture convergence. Specifically, the precipitable water values at which precipitation is balanced independently by evaporation versus by moisture convergence define a critical normalized precipitable water, pwnc. This is a measure of convective inhibition that separates tropical precipitation into two regimes: a local evaporation-controlled regime with widespread drizzle and a precipitable water–controlled regime. Most of the 17 CMIP6 historical simulations examined here have higher pwnc compared to ERA5, and more frequently they operate in the drizzle regime. When compared to observations, they overestimate precipitation over the high-evaporation oceanic regions off the equator, thereby producing a “double ITCZ” feature, while underestimating precipitation over the large tropical landmasses and over the climatologically moist oceanic regions near the equator. The responses to warming under the SSP585 scenario are also examined using the normalized precipitable water framework. It is shown that the critical normalized precipitable water value at which evaporation versus moisture convergence balance precipitation decreases as a result of the competing dynamic and thermodynamic responses to warming, resulting in an increase in drizzle and total precipitation. Statistically significant historical trends corresponding to the thermodynamic and dynamic changes are detected in ERA5 and in low-intensity drizzle precipitation in the PERSIANN precipitation dataset

Presented by

Samson Hagos

Institution

Pacific Northwest National Laboratory

Keywords

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Available May 25th 15:05 PM EDT

Critical Updraft Quantities in LES Models of Shallow to Deep Convective Transitions

Scott Powell

Abstract

Idealized simulations of tropical, marine convection depict shallow, non-precipitating cumuli located beneath the 0C level transitioning into cumulonimbi that reach the upper troposphere. Duration of the transitions depended on the static stability of initial sounding profiles with identical relative humidity used to force the simulations. Except for the most unstable initial sounding, the transitions featured rapid development of deep convection over 1–4 hours, accompanied by increasing rain rate. The key quantity that determined when shallow convection transitioned into deep clouds was vertical acceleration inside the lowest 1–1.5 km of cloudy updrafts above cloud base. When domain-mean total vertical acceleration in this layer increased to just above zero, deep convection became prevalent. Of the simulations that experienced a rapid transition, the domain-mean updraft temperature increased over a ~30-minute long period by ~0.04C relative to environmental temperature in the 1–1.5 km above cloud base, starting ~30 minutes prior to the rapid increase in rain rate. This increase closely followed the time at which moist enthalpy of updrafts in the boundary layer first exceeded that of boundary layer air outside of updrafts. The results suggest that in environments that are sufficiently moist for deep convection, tiny changes in mean updraft or environmental temperature across an area may control when shallow-to-deep convection occurs, and that changes in updraft temperature might be connected directly to variable thermodynamic characteristics of parent updrafts in the boundary layer.

Presented by

Scott Powell

Institution

Naval Postgraduate School

Keywords

Precipitation, Cloud Life Cycle, LES

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Available May 25, 1500–1600 EDT (1200–1300 PDT)

A Global High-resolution Mesoscale Convective System Tracking Database

Zhe Feng, L. Ruby Leung , Nana Liu , Jingyu Wang , Robert A. Houze Jr, Jianfeng Li , Joseph C. Hardin

Abstract

The largest type of organized convective storm, known as the mesoscale convective system (MCS), plays an important role in the global hydrological and energy cycles. We develop a new methodology to construct a global (60°S–60°N) long-term (2000-2019) high-resolution (~10-km, hourly) MCS database by tracking MCS jointly using geostationary satellite infrared brightness temperature (Tb) and precipitation feature (PF) characteristics from the Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation datasets. Results show that MCSs account for over 50% of annual total rainfall across most of the tropical belt and in select regions of the midlatitudes, with a strong seasonality over many regions of the globe. The longest-lived MCSs preferentially occur over the subtropical oceans. The land MCSs have higher cloud-tops associated with more intense convection, and oceanic MCSs have much higher rainfall production. By combining the MCS tracking database with a GPM Ku-band radar PF database and latent heating retrievals, we further examine the global MCS latent heating characteristics. We find that MCS latent heating profiles are top heavier in the sub-tropics and mid-latitudes than those in the tropics. Oceanic MCSs have larger magnitudes of stratiform latent heating than land for both tropics and mid-latitudes. Most mid-latitude MCSs have a relatively high (> 70%) stratiform rain fraction while this is not the case for tropical MCSs. This global database provides significant opportunities for observational and modeling studies of MCSs, their characteristics and roles in ocean-atmosphere interactions and in regional and global water and energy cycles.

Presented by

Zhe Feng

Institution

Pacific Northwest National Laboratory

Keywords

Mesoscale convection, global climatology, precipitation, storm tracking, satellite observation

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Available May 25th, 15:00-16:00 EDT

▼ 4. Ocean Studies and Observing Needs Back to top

A study on the Correlation between Madden Julian Oscillation (MJO) and Ocean Current patterns in the Waters of the Sunda Strait

Yosafat Donni Haryanto, Niken Astrid Septyar, Adji Syarifah Happy, Nelly Florida Riama

Abstract

Ocean current is defined as the movement of sea water masses due to the dynamic relationship between the atmosphere and the oceans. One of the weather phenomena in the atmosphere which can affect the conditions of the ocean’s dynamics is the Madden Julian Oscillation (MJO). MJO is a movement of convection areas propagating eastward from the Indian Ocean to the Pacific Ocean over a 40 – 50 days period. Previous studies have shown that MJO activity can affect various parameters such as wind direction and speed, sea surface temperature, and ocean current patterns in the area in which it passes. This study aimed to determine changes in the pattern of ocean currents in the waters of the Sunda Strait when MJO is in an active and inactive phases. The dates and activities of MJO were determined using Real-Time Multivarate MJO (RMM) Index of Series 1 and Series 2 (RMM1 and RMM2) data. This research was conducted by utilizing MIKE 21 numerical model to describe the ocean currents when the MJO is in an active or inactive phase in the waters of the Sunda Strait. Data of bathymetry, coastline, wind, surface pressure, and tides were needed to run the model. Based on the analysis of the study, it was found that MJO activity influenced on the changes of ocean current patterns in the Sunda Strait waters. In addition, there was a significant influence on changes in the direction of ocean currents which occurred every 12 hours. The average current velocity also increased ranging from 0.5 – 1 m/s when the MJO was in the active phase.

Presented by

Yosafat Donni Haryanto

Institution

BMKG

Keywords

ocean current, MJO, Sunda Strait

Equatorial ENSO Physics

Allan J. Clarke & Xiaolin Zhang

Abstract

Past work has shown that the standard raw monthly anomaly sea surface temperature (SST) El Niño index Niño 3.4 is strongly phase locked to the seasonal cycle. With a correlation r=0.93 Niño3.4 = S(m)Y(a) with S(m) as an unchanging 12 calendar-month function that increases in amplitude from April to November, and then decreases from January to March. The annual function Y(a) is large and positive for an El Niño and large in magnitude and negative for a La Niña, the negligible correlation from one year a to the next year a+1 being associated with the persistence barrier from March to April. Since S(m) is unchanging, the basic dynamics of El Niño is not diverse; very different off equatorial variation is sometimes associated with the same S(m). Physically the growth from April to November is associated with a coupled ocean atmosphere instability at the eastern edge of the western equatorial Pacific warm pool. After reaching a maximum at the end of the calendar year the coupled instability dies as the anomalous deep atmospheric convection and the zonal wind anomalies follow the warmer water south of the equator during the southern hemisphere summer. The anomalous equatorial warm water volume (EqWWV) leads Niño3.4 and therefore is able to link consecutive El Niño years and provide long lead prediction. Observationally-verified theory shows that the EqWWV lead is not due to heat content but rather to zonal flow acceleration advecting the warm pool edge back to its original position when the zonal wind anomaly moves south of the equator and no longer forces the equatorial flow.

Presented by

Allan Clarke <aclarke@fsu.edu>

Institution

Florida State University, Department of Earth,Ocean and Atmospheric Science & University of Hamburg

Keywords

El Nino, coupled instability, warm water volume, ENSO prediction

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Available May 25th 3pm to 4pm EDT

IRISS: IR In situ Skin & Sub-skin Temperature Measurements from USVs and buoys

Andy Jessup and Elizabeth Thompson

Abstract

Accurate ocean surface skin temperature is critical to estimating heat flux for global climate monitoring and modeling. Skin temperature models combined with ship-based measurements of bulk temperature at O(cm) depths have demonstrated adequate accuracy. A comparable approach for skin temperature estimates from USVs and buoys is impractical. Recent advances in infrared radiometer stability indicate that radiometric measurements of skin temperature from these platforms is achievable. Here we report on the development of the IRISS (InfraRed In situ Skin and Subskin) instrument to measure skin and subskin temperature from USVs and buoys with accuracy comparable to ship-based systems.

Presented by

Andy Jessup

Institution

Applied Physics Laboratory, University of Washington and NOAA-ESRL

Keywords

skin temperature, infrared, heat flux, USV, saildrone, buoy

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Available May 25, 2021 15:05 - 16:05 EDT

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The role of Tropical Instability Waves in modulating water mass transformation

Anna-Lena Deppenmeier, Frank O. Bryan, William S. Kessler, LuAnne Thompson

Abstract

The tropical Pacific plays an integral role in the coupled global climate system. Surface and subsurface variability on the eastern tropical Pacific cold tongue impacts the Walker circulation as well as ocean heat uptake and redistribution. Our recent analysis has shown that La Niña conditions are much more efficient than El Niño conditions in fostering water mass transformation and as a consequence associated ocean heat uptake in the cold tongue. These inter-annual time scales, however, are difficult to capture during a process study field campaign.

Using a high resolution ocean model with full heat budget output, we investigate the variability of cross-isothermal velocities and underlying physical processes associated with the seasonal cycle and with the passage of tropical instability waves (weeks). Preliminary analysis shows that periods of high tropical instability wave activity coincide with enhanced water mass transformation in the thermocline. Tropical instability waves cumulatively enhance water mass transformation from cold to warm without a corresponding transformation from warm to cold. We explore the rectification of the tropical instability wave’s impact on water mass transformation, and examine how this contributes to variations associated with the seasonal cycle. We also explore the latitudinal and longitudinal dependence of water mass transformation associated with tropical instability waves, and aim to determine length scales needed to adequately sample these processes.

Presented by

Anna-Lena Deppenmeier

Institution

NCAR, CGD; NOAA PMEL; University of Washington

Keywords

Tropical Instability Waves, water mass transformation

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Available May 25th 1:05-2:30MDT (3:05-4:30EDT)

The need for new observations of near-surface ocean-side interaction processes for physical and chemical flux modeling

C.W. Fairall1, Elizabeth Thompson1, Byron Blomquist1, James Edson2, Andy Jessup3

Abstract

The COARE family of flux parameterizations have been advancing steadily for more than two decades. Recent field programs and theoretical progress have highlighted the need to improve the treatment of ocean-side processes. The warm layer and cool skin phenomena, absorption of solar radiation, partitioning of wave vs viscous stress, the role of air entrainment by breaking waves in gas transfer, and chemical enhancement of CO2 flux are all topics where answers are needed. A new initiative for theoretical, numerical, modeling, and observational study is needed. In this talk we will summarize recent work on these topics and outline an experimental strategy.

Presented by

Chris Fairall

Institution

NOAA Physical Science Laboratory1, Woods Hole Oceanographic Institution2, University Washington/APL3

Keywords

Air-sea flux, COARE, biogenic gas transfer

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Available May 25 18:30 EDT

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Ocean mixing in the equatorial Pacific cold tongue

D. B. Whitt, D. A. Cherian, S. Bachman, R. Holmes, R-C. Lien, W. Large

Abstract

Ocean mixing in the equatorial Pacific cold tongue plays a key role in the sea-surface temperature, tracer, and momentum budgets. However, observations of turbulence are limited to a handful of field experiments lasting from a few days to one month at 0 N, 140 W, and the key turbulent fluxes can only be inferred. Although explicit simulations of turbulence resolve these fluxes, the required large eddy simulations (LES) are costly and thus also limited to a few weeks. A two-fold hypothesis motivates this contribution to the PUMP pre-field modelling experiments in support of TPOS: 1) that there exist useful relationships between the surface wind, wave, and buoyancy forcing, oceanic shear and stratification, and turbulent mixing, but 2) the state space is insufficiently sampled to understand these relationships and represent them in ocean general circulation models (OGCM). To address the lack of data, we simulated 35 continuous days of upper ocean turbulence using LES during October-November 1985 at sites in two regions (70 days in total) of the cold tongue: 0 N, 140 W and 3 N, 140 W. The model reproduces many features of the observed turbulence at 0,140W, including the “deep-cycle turbulence” (DCT) observed by Gregg et al. (1985) Nature and the turbulent pulses every few hours during the night and in the early morning. Furthermore, the results at 3 N support the hypothesis advanced by Cherian et al. (2021) JPO that strong, but intermittent DCT occurs to the north of the equator in the presence of strong vertical shear associated with Tropical Instability Waves.

The new results are as follows: 1) by extending the simulation of Cherian et al. over 18 years, we show that ocean mixing is a stronger driver of sea-surface temperature than surface heat fluxes over most of the cold tongue most of the time. 2) We find that the strength of vertical mixing in DCT scales with the vertical shear of the upper-ocean currents and surface wind stress, but turbulent diffusivity is not well correlated with gradient Richardson number as in some parameterizations. 3) We apply the new scaling to show that turbulent carbon fluxes in DCT dominate air-sea carbon fluxes at most latitudes in a hydrographic section across the cold tongue.

The results underscore the need for more extensive measurements of vertical profiles of shear, stratification and turbulence to relate the spatio-temporal structures to the surface forcing across the cold tongue. Ideally, some of these measurements would be made in conjunction with ocean biogeochemical measurements that would facilitate future work to build understanding of the links between ocean mixing, the carbon cycle, and marine ecosystems.

Presented by

Dan Whitt

Institution

NASA ARC, NCAR CGD, UNSW, UW/APL

Keywords

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Available May 25 15:05-16:00ET

Tropical Instability Waves force deep-cycle turbulence in the cold cusp between 3°N and 5°N

Deepak Cherian, Daniel Whitt, Ryan Holmes, Ren-Chieh Lien, Scott Bachman, William Large

Abstract

The equatorial Pacific cold tongue is a site of large heat absorption by the ocean. This heat uptake is enhanced by a daily cycle of shear turbulence beneath the mixed layer — “deep-cycle turbulence” — that removes heat from the sea surface and deposits it in the upper flank of the Equatorial Undercurrent. Deep-cycle turbulence results when turbulence is triggered daily in sheared and stratified flow that is marginally stable (gradient Richardson number Ri ≈ 0:25). Deep-cycle turbulence has been observed on numerous occasions in the cold tongue at 0°N, 140°W, and may be modulated by Tropical Instability Waves (TIWs).

Here we use a primitive equation regional simulation of the cold tongue to show that deep-cycle turbulence may also occur off the equator within TIW cold cusps where the flow is marginally stable. In the cold cusp, pre-existing equatorial zonal shear u_z is enhanced by horizontal vortex stretching near the equator, and subsequently modified by horizontal vortex tilting terms to generate meridional shear v_z off of the equator. Parameterized turbulence in the sheared flow of the cold cusp is triggered daily by the descent of the surface mixing layer associated with the weakening of the stabilizing surface buoyancy flux in the afternoon. Observational evidence for off-equatorial deep-cycle turbulence is restricted to a few CTD casts, which when combined with shear from shipboard ADCP data suggest the presence of marginally stable flow in TIW cold cusps. This study motivates further observational campaigns to characterize the modulation of deep-cycle turbulence by TIWs both on and off the equator.

Presented by

Deepak Cherian

Institution

National Center for Atmospheric Research

Keywords

turbulence, TIW, mixing

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Available May 25 3:05pm-4:05pm EDT

Mechanism of Interannual Cross-equatorial Overturning Anomalies in the Pacific Ocean- An Investigation using Ocean Reanalysis

Devanarayana Rao Mohan Rao and Neil F. Tandon

Abstract

The meridional overturning circulation (MOC) transports heat and mass latitudinally from the tropics to the high latitude and vice versa. Recent evidence shows that the variability of MOC in the Indian and Pacific Oceans (PMOC) dominates the variability of the global MOC on interannual timescales. It is known that this variability is characterized by a prominent cross-equatorial cell (CEC) spanning the tropics between 20°S and 20°N. This CEC is potentially an important influence on interannual climate variability, but the mechanism responsible for this CEC is not understood. This study seeks to elucidate the mechanism of the CEC in the Pacific Ocean using version 4.2 of the Estimating the Circulation and Climate of the Ocean (ECCO) state estimate. Our investigation shows the mechanism responsible for CEC can be conceptualized by following mechanistic chain: 1) Anomalous winds produce equatorially antisymmetric anomalies of zonal mean sea surface temperature (SST) in the Pacific Ocean, 2) These temperature anomalies generate equatorially antisymmetric anomalies of sea surface height (SSH), 3) The SSH anomalies generate a cross-equatorial flow in the upper Pacific Ocean (above approximately 1000 m), and 4)This anomalous cross-equatorial flow in the upper layers drives compensating circulation in the deep Pacific. This mechanism contrasts with that responsible for anomalous cross-equatorial overturning on seasonal timescales, which is primarily the Ekman response to equatorially antisymmetric anomalies of zonal wind stress. On interannual timescales, however, the zonal wind stress anomalies associated with the CEC are equatorially symmetric, and steric SSH variations are the dominant driver of the CEC. The findings of this research likely have important implications for coupled ocean-atmosphere processes in the tropical Pacific Ocean as well as changes in oceanic heat content and sea level.

Presented by

Devanarayana Rao Mohan Rao

Institution

York University, Toronto, Canada

Keywords

Pacific Meridional Overturning Circulation, Ocean Reanalysis, ECCO, Interannual Variability

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Available 15:05 -16:05 EDT, May 25th, 2021

Saildrone: Uncrewed Surface Vehicle for surface current and air-sea flux observation

Dongxiao Zhang(1,2), Meghan F. Cronin(2), Samantha Wills(1,2) , Christian Meinig(2), Noah Lawrence-Slava(2), Richard Jenkins(3) and David Peacock(3)

Abstract

Over the past decade, significant progress has been made in the global ocean observing system (GOOS), which is monitoring much of the upper ocean on a global scale in real time with multiple observing platforms. However, observation of air-sea fluxes has been relying on fixed surface moored buoys and research and voluntary ships with limited spatial coverage. As a result, the current GOOS is not able to adequately observe the air-sea interaction processes across fronts and eddies. A recent technology development, the saildrone, is an Uncrewed Surface Vehicle (USV) powered by wind and solar energy with a range of more than 6,000 nautical miles, making it a potential platform to sample across fronts and weather systems over the global ocean. To make the saildrones capable of observing air-sea interaction processes, we have installed sensors with equivalent or better quality than those currently used on Tropical Atmosphere and Ocean (TAO) buoys for air-sea flux measurements, and a 300-kHz Acoustic Doppler Current Profiler for upper ocean current measurements. So far, three pilot Saildrone Missions have been completed in the tropical Pacific, as part of the Tropical Pacific Observing System (TPOS)-2020 project: one mission with two saildrones deployed and recovered from California; the other two deployed and recovered four saildrones from Honolulu, Hawaii. All missions reached the equator, sampled across the tropical Pacific cold tongue fronts and oceanic vortices and sent data in realtime to the GTS. Data suggest the importance of high quality simultaneous measurements of ocean currents and air-sea state variables in air-sea flux observation. Using COARE3.6 bulk algorithm, we demonstrate that lack of surface current measurement can lead to up to 60% error in wind stress and 20% error in latent and sensible heat fluxes in the tropical Pacific, especially near the equator, at the front of Tropical Instability vortices, and in the Intertropical Covergence Zone (ITCZ). Implication of these results in current-wind feedback and mesoscale air-sea interaction processes and the potential of saildrones for air-sea interaction studies in the Tropical Pacific will also be discussed.

Presented by

Dongxiao Zhang

Institution

1 CICOES/University of Washington; 2 NOAA Pacific Marine Environmental Laboratory; 3 Saildrone, Inc.

Keywords

air-sea fluxes, saildrone, UxS, TIW, wind stress, fronts

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Available 5/25 15:05-16:05 EDT

The importance of vertical mixing in the tropical ocean: the need to capture small vertical scales

Kelvin Richards, Andrei Natarov, Yanli Jia, and H. Annamalai

Abstract

Turbulent mixing in the equatorial thermocline has been shown to impact not only the ocean but its coupling with the atmosphere. Recent studies have demonstrated the importance of the vertical distribution of the effective vertical diffusion coefficient, and the associated mixing of heat and salt, across the width of the equatorial Pacific. Here we review the factors affecting mixing and its vertical distribution using observations, process models and GCMs. The importance of flow features with relatively small vertical scale, such as wind generated internal waves and flow instabilities, is emphasized. We stress the need to determine the spatial and temporal variability of such processes, and the associated mixing, and discuss how this may be achieved through regional ocean observational process studies and basin-scale monitoring.

Presented by

Kelvin Richards

Institution

IPRC, University of Hawai`i at Mānoa

Keywords

ocean turbulence, scale interactions

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Available Tuesday May 25, 15:00-16:00 EDT

Spatiotemporal characteristics of Indian Ocean rain layers

Kyle Shackelford, Charlotte DeMott, Peter Jan van Leeuwen

Abstract

Surface freshening through precipitation can act to stably stratify the upper ocean, forming a rain layer. Rain layers inhibit subsurface vertical mixing, consequently altering near surface profiles of temperature and salinity, and surface fluxes. For this study, we focus on rain layer frequency, intensity, and duration in the Indian Ocean as a function of meteorological surface forcing.

The General Ocean Turbulence Model (GOTM) is used to simulate rain layers in the Indian Ocean. GOTM is initialized and calibrated using observations of the upper ocean collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. The fine-scale vertical resolution of upper ocean observations collected during DYNAMO allow for robust comparisons of modeled and observed stability profiles. Results indicate that the impact of rain layers on upper ocean temperature and salinity profiles is effectively captured by a 1-D ocean model. Spatiotemporal characteristics of equatorial Indian Ocean rain layers are then investigated by forcing a 2-D array of GOTM columns with WRF model output. Future steps focus on investigation of ocean feedback to atmospheric convection through implementation of a coupled ocean-atmosphere model.

Presented by

Kyle Shackelford <Kyle.Shackelford@colostate.edu>

Institution

Colorado State University, Department of Atmospheric Science

Keywords

stable layers, sea surface temperature, sea surface salinity, air-sea, in-situ observations

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Available May 25, 3:05-4:00 EDT

Interaction between the TIWs and the Intraseasonal equatorial Kelvin wave in the Pacific

Gabriela Escobar, Julien Boucharel, Boris Dewitte

Abstract

The intraseasonal Kelvin waves (IKWs) and tropical instability waves (TIWs) are essential components of the tropical Pacific coupled climate variability. They both modulate the intraseasonal surface and thermocline variability on the central-eastern Pacific and can trigger an interactive feedback between the seasonal and interannual timescales (e.g. the El Niño Southern Oscillation (ENSO)). Throughout their eastward propagation along the equator, the IKWs can modulate the thermocline depth and either amplify (downwelling IKW) or dampen (upwelling IKW) the Bjerknes feedback, thus kick-starting or suppressing an El Niño event. By mixing less/more warm off-equatorial and cold tongue waters during El Niño/La Niña, TIWs can contribute to the ENSO asymmetry. Theoretical studies and a few observational case studies suggest that TIWs and IKWs can interact nonlinearly. However, owing to the chaotic nature of TIWs, observational evidence that such process take place consistently has not been established thus far. In this study, we document for the first time their interaction from satellite observations over a period spanning 1993-2018. From complex empirical orthogonal functions analysis and sea level decomposition into meridional modes, we evidence a statistical intraseasonal mode having a projection on both the equatorial Kelvin wave and the TIWs accounting for 10% of the explained variance of sea level intraseasonal anomalies, comparable to the first dominant mode (11%) accounting for TIWs activity not related to IKWs. This IKW-TIW mode is particularly active in austral summer and not necessarily during ENSO years. We show that non-linear dynamical heating (NDH) in the Eastern equatorial Pacific associated to this intraseasonal mode can be as large as that for interannual timescales. Implications for understanding the eastern tropical Pacific heat budget and ENSO variability are discussed.

Presented by

Maria Gabriela Escobar Franco

Institution

University of Toulouse III - Paul Sabatier/ LEGOS

Keywords

Equatorial Kelvin Wave, Tropical Instability Waves, intraseasonal timescale

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Available Available 15:05 -16:05 EDT, May 25th, 2021

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▼ 5. OSSEs, Data Assimilation, Reanalyses Back to top

Impact of the Ocean In-situ Observations on the ECMWF Seasonal Forecasting System

Magdalena A. Balmaseda, Michel Mayer, Retish Senan, Beena Balan Sarojini, Steffen Tiestche, Tim Stockdale, Frederic Vitart, Hao Zuo

Abstract

We evaluate the impact of the in-situ ocean observations on seasonal forecasts. A series of seasonal reforecasts have been conducted for the period 1993-2015, in which different sets of ocean observations were withdrawn in the production of the ocean initial conditions. By comparing the different reforecast sets, it is possible to assess the impact on the forecast of ocean and atmospheric variables. Results show that the in-situ observations have a profound and significant impact on the mean state of forecast ocean and atmospheric variables, and can be classified into different categories: i) impact due to local air-sea interaction, a direct consequence of changes in the mixed layer in the ocean initial conditions, and visible in the early stages of the forecasts; ii) changes due to different ocean dynamical balances, most visible in the Equatorial Pacific at time scales of 3-4 months; iii) changes to the atmospheric circulation resulting from changes in large scale SST gradients; these are non-local, mediated by the atmospheric bridge, and depend on the differential impact of the observing system in different regions. Additional experiments indicate that there is another sort of changes, due to slow ocean dynamics, which are visible at timescales longer than one year.

Presented by

Magdalena Balmaseda

Institution

ECMWF

Keywords

The Tropical Pacific Ocean State Estimate (TPOSE) Resource

Ariane Verdy, Matt Mazloff, Bruce Cornuelle

Abstract

A one-third degree regional state estimate is being produced by assimilating data from the Tropical Pacific Observing System (TPOS) for the period 2010 to 2019. To capture mesoscale dynamics, we use a 4-Dimensional Variational (4D-Var) method to adjust initial conditions and atmospheric forcing for a series of four month simulations to match the observations as closely as possible. The adjusted simulations are staggered by two months, and the state estimate is made by patching together overlapping windows. The state estimate provides a dynamically-consistent, property-conserving, large-scale framework for investigating the mechanisms involved in events such as the 2015-16 El Nino, or the variability in the eastern edge of the warm pool.

The state estimate is being extended to new products: a higher-resolution (one-sixth degree) model run is forced with adjusted initial conditions and atmospheric forcing from the coarse-resolution hindcasts and is being coupled to a biogeochemical model. This TPOSE resource can provide a background state for giving context to process studies, or the infrastructure could be used to create a high-resolution state estimate utilizing observations taken during a process study.

The 4D-Var method utilizes the adjoint model, which also provides the technology to efficiently compute sensitivities for a wide range of quantities of interest (QoIs) to model properties and inputs. This is an advantage over standard forward modeling sensitivity studies, where it is not feasible to perturb every region of the model that might affect a given QoI. The adjoint sensitivity analysis has been used in the tropical Pacific to quantify the sensitivity of the Nino-3 SST to wind stress, showing the combined effects of different dynamical pathways from wind stress change to SST change: tropical instability waves, Kelvin waves, equatorial Rossby waves, and advection. In the context of process experiments, this can be used to identify the regions where previous forcing or ocean state influences the target region, which in turn can be used to design observing strategies.

Presented by

Ariane Verdy

Institution

Scripps Institution of Oceanography, UCSD

Keywords

Data Assimilation, Modeling

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Available Wednesday, May 26 · 3:00 - 4:00 PM EDT

Importance of Off-equatorial Subsurface Preconditions for ENSO Evolution and Predictability

Caihong Wen, Arun Kumar, Michelle L’ Heureux, Yan Xue and Emily Becker

Abstract

Oceanic memory associated with subsurface temperature anomalies along the equatorial thermocline has long been recognized as an important source of ENSO predictability. However, the relationship between the equatorial Pacific Warm Water Volume (WWV) as an ENSO precursor and ENSO SST weakened substantially after ~2000, coinciding with a degradation in dynamical model ENSO prediction skill. Using a set of ocean reanalysis, we accessed factors responsible for the variation of the equatorial Pacific Ocean thermocline during 1982-2019. It is found that off-equatorial thermocline temperature anomalies carried equatorward by the mean meridional currents associated with Pacific Tropical Cells play an important role in modulating the central equatorial thermocline variations, which is rarely discussed in the literature. Further, ENSO events are delineated into two groups based on precursor mechanisms: the western equatorial type (WEP) ENSO, when the central equatorial thermocline is mainly influenced by the zonal propagation of anomalies from the western Pacific, and the off-equatorial central Pacific (OCP) ENSO, when off-equatorial central thermocline anomalies play the primary role. WWV is found to precede all WEP ENSO by 6-9 months, while the correlation is substantially lower for OCP ENSO events. In contrast, the central tropical Pacific (CTP) precursor, which includes off-equatorial thermocline signals, has a very robust lead correlation with the OCP ENSO. Most OCP ENSO events are found to follow the same ENSO conditions, and the number of OCP ENSO increased substantially since the 21st century. These results highlight the importance of monitoring off-equatorial subsurface preconditions (temperature & meridional current) for ENSO prediction and to understand multi-year ENSO. The implication of our results on future observing system design is also discussed.

Presented by

Caihong Wen

Institution

NOAA/Climate Prediction Center

Keywords

ENSO prediction and predictability, Meridional heat transport, ENSO precursors, ocean reanalysis

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Available May 26 3-4:30pm EDT

Diagnosing Sources of Tropical SST Drift in Coupled Forecast Models

Charlotte DeMott, Aneesh Subramanian, Kris Karnauskas, Ho-Hsuan Wei, Magdalena Balmaseda, Frederic Vitart, and Beena Balan Sarojini

Abstract

Sea surface temperatures (SSTs) in coupled forecast models exhibit systematic drift away from their initialized state and toward the models’ inherent climatological states. Patterns of SST drift are highly correlated with patterns of column-integrated water vapor (CWV) drift and thus have the potential to affect the prediction of tropical rainfall through the tight coupling between deep convection and CWV in the tropics. Patterns of SST drift may therefore influence prediction skill of the tropical Madden-Julian oscillation, whose eastward propagation depends critically upon horizontal gradients of the background moisture.

In this study, we diagnose sources of climatological SST drift in five coupled forecast models participating in the international S2S Prediction Project. SST drift that is driven by drift in the net surface energy flux (Qnet) is estimated by the regression relationship between climatological SST and Qnet tendencies as a function of forecast lead time. The residual SST drift (i.e., the part that is uncorrelated with Qnet drift) can be considered as that associated with drift in ocean processes, such as changes in ocean mixed layer depth or shear driven mixing. With this approach, SST drift that is the result of model initialization shock can often be distinguished from systematic drift to a model’s preferred mean state. For the systematic SST drift, our results demonstrate that the relative contributions by Qnet drift and ocean dynamics drift vary widely among models and throughout the tropics.

Presented by

Charlotte DeMott

Institution

Colorado State University

Keywords

ocean forecasts, model bias, process understanding

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Available May 26, 2021 3:35 - 4:05 EDT

Effect of Rain-Adjusted Satellite Sea Surface Salinity on ENSO Predictions from the GMAO S2S Forecast System

E. Hackert1, S. Akella1, R. Kovach12, K. Nakada12, A. Borovikov12, A. Molod1, K. Drushka3, and M. Jacob4

Abstract

The El Niño/Southern Oscillation (ENSO) phenomenon has a significant impact on climate variability throughout the world and so has been the key focus for improving coupled ocean-atmosphere forecasts. Assimilation of satellite altimetry and subsurface temperature and salinity from (mostly) Argo helps to improve the initialization of the thermocline, while satellite SST aids in constraining surface heat-fluxes, leading to improved short-term forecasts of the coupled system. Recent studies (e.g., Martin et al., 2019, Tranchant et al., 2018) have demonstrated that improving the near-surface density and mixing through assimilation of satellite sea surface salinity (SSS) have improved the ocean state, and have led to improved seasonal predictions (e.g., Hackert et al., 2020).

For expediency, most projects that assimilate SSS, do so as if these data were observed at the top model layer (typically 5 m) instead of at the surface (i.e., top 1 cm), where the satellite measures SSS. In rainy regions, where buoyant water sits as a fresh lens at the surface following rainfall , this assumption is likely invalid. Therefore, we adjust SSS so that it more accurately represents the salinity at 5 m. The Rain Impact Model (RIM – Santos-Garcia et al., 2014) uses a simple diffusion model (Asher et al., 2014) to determine the near surface salinity gradient (i.e., 1 cm to 5 m). The Aquarius (V5) satellite SSS data are modified using the RIM near-surface salinity gradient, so the salinity values are now valid at 5 m (we call this AQUARIUS_RIM).

We assess the impact of satellite SSS observations for near-surface dynamics within ocean reanalyses and how these impact dynamical ENSO forecasts, using the NASA GMAO Sub-seasonal to Seasonal coupled forecast system (S2S-v3, Molod et al., 2020). For all reanalysis experiments, all available along-track absolute dynamic topography and in situ observations are assimilated using the LETKF scheme (Penny et al., 2013). One reanalysis assimilates satellite SSS data as if it were 5 m data (as before). An additional reanalysis is performed assimilating the AQUARIUS_RIM data that represents the bulk salinity at 5 m.

Validation statistics are compared for experiments that assimilate SSS (sub-optimally as before) versus the AQUARIUS_RIM. AQUARIUS_RIM minus AQUARIUS reanalyses show a salting near the equator leading to a shoaling of the mixed layer depth (MLD) and a relative equatorial westerly wind anomaly. Shallower MLD and westerly wind anomaly both would lead to amplification of the downwelling Kelvin wave associated with the 2015 El Niño. Coupled forecasts that are initialized from these reanalyses show that improved SSS estimates upgrade density and near-surface mixing, leading to more accurate coupled air/sea interaction and better ENSO forecasts.

Presented by

Eric Hackert <eric.hackert@nasa.gov>

Institution

1 NASA/GMAO, 2 SSAI, 3 Applied Physics Laboratory, 4 University of Central Florida

Keywords

salinity assimilation, ENSO prediction

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Available May 26, 2021 at 15:05 - 16:00 Eastern Daylight Time (EDT)

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OSSE studies for the Tropical Pacific Observing System

Jieshun Zhu1, Arun Kumar1, Guillaume Vernieres2, Travis Sluka2

Abstract

In this study, a series of ocean observing system simulation experiments (OSSEs) are conducted for the Topical Pacific Observing System (TPOS). The experiments are based on the new ocean data assimilation system that is under development at the Joint Center for Satellite Data Assimilation (JCSDA) and the Environmental Modeling Center (EMC)/National Centers for Environmental Prediction (NCEP). The atmospheric forcing and synthetic ocean observations are generated from a nature run, which is based on the modified CFSv2 with ocean vertical resolution of 1-meter near the ocean surface. Firstly, the current configuration of in situ TPOS observations is evaluated with a focus on the Pacific tropical moored buoy array (TMA; i.e., the collective TAO/TRITON moored array) and Argo. To separate the effects of TMA and Argo in TPOS, the synthetic observations were constructed following their present distributions, both separately and jointly. Our experiments include a free run without assimilating any observations, and assimilation runs with the TMA and Argo “observations” assimilated separately or jointly. The experiments were compared for variability at different time scales [low-frequency (>90days), intraseasonal (20~90days) and high-frequency (<20days)]. It was found that (1) both TMA and Argo effectively improve the estimation of mean states and low-frequency variations; (2) on the intraseasonal time scale, Argo provides significant improvements more so than TMA (except for regions close to TMA sites); (3) on the high-frequency time scale, both TMA and Argo have clear deficits (for TMA, limited improvements were present close to TMA sites). Secondly, the proposed TMA configuration recommended by the TPOS 2020 project is evaluated. Compared to the existing TMA configuration, the recommended modifications include changes in mooring sites, more subsurface salinity measurements, and others (e.g., ocean currents). The new TMA is evaluated by comparing two experiments, which assimilate synthetic observations constructed based on existing and proposed TMA configurations, respectively.

Presented by

Jieshun Zhu <Jieshun.zhu@noaa.gov>

Institution

1Climate Prediction Center, NOAA/NWS/NCEP, College Park, Maryland, USA 2Joint Center for Satellite Data Assimilation, NOAA, College Park, Maryland, USA

Keywords

Tropical Pacific Observing System; data assimilation; OSSE

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Available May 26 · 3:05 – 4:05pm EDT

Evaluation of a coupled atmosphere-ocean reanalysis using the tropical Pacific mooring data

Yosuke Fujii, Chiaki Kobayashi, Ichiro Ishikawa, Yuhei Takaya

Abstract

In this study, we evaluated tropical precipitation and sea surface air temperature (SAT) fields and their relationship with sea surface temperature (SST) represented by the coupled atmosphere-ocean reanalysis generated in the Meteorological Research Institute (MRI) of the Japan Meteorological Agency (JMA) mainly using the tropical Pacific mooring data. The coupled reanalysis was conducted using a coupled atmosphere-ocean data assimilation system, MRI-CDA1, which is constituted of the coupled atmosphere-ocean general circulation model and separated atmosphere and ocean analysis routines adopted in JMA’s operational weather and climate prediction systems. In the tropical Pacific, warm SST promotes atmospheric convections and thus precipitation increases after the SST peak. The clouds accompanying the precipitation cut the short waves and causes decrease of SST. This relationship was well reproduced in the coupled reanalysis. However, SST variation in the coupled reanalysis lagged the actual variation of SST. A detailed analysis indicated that the too-rapid propagation of the SST variability due to the near-surface ocean mixing process causes this difference. The atmosphere-ocean coupling generated SST variations associated with tropical instability waves, and the SAT field responded to SST variations. The SST-precipitation and SST-SAT relationships on the weather timescale were also recovered in the coupled reanalysis, although they are hardly seen in an uncoupled reanalysis. From this study, we realized the necessity of oceanic temperature data with high vertical and temporal resolutions for the development and validation of the near-surface oceanic processes, such as downward propagation of the heat signals, in a coupled model/CDA system. We expect the enhanced observation in the oceanic mixed layer by the tropical Pacific mooring buoy array planned by the Topical Pacific Observing System 2020 (TPOS2020) project will make an essential contribution to this purpose.

Presented by

Yosuke Fujii

Institution

JMA/MRI

Keywords

Coupled Data Assimilation, Oceanic Mixed Layer, SST-precipitation relationship

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Available May 24th, 15:20-16:00 EDT

▼ 6. Observing the Ocean-Atmosphere Transition Zone Back to top

In situ and satellite flux observations in the tropical Pacific

Carol Anne Clayson, James B. Edson, Chelle Gentemann, Tony Lee, Aneesh Subramanian, Susan Wijffels

Abstract

Marine physicists have made significant progress in recent decades in our ability to directly measure surface fluxes from research vessels and specialized platforms. These platforms utilize Direct Covariance Flux Systems (DCFS) to remove platform motion from the measured wind speeds to measure the flux directly. Over the past decade or so, researchers have begun to collect long time series, O(year), of momentum and buoyancy fluxes from surface moorings. The instrumentation on these moorings experience less flow distortion and measure a wider variety of conditions given their longer deployments than typical for oceanographic air-sea field campaigns on research vessels. The latest generation of DCFS have been deployed in the Tropics in field campaigns. A significant achievement was reached during the NASA SPURS field program with the inclusion of LI-COR infrared gas analyzers to make fast-response humidity measurements on a surface mooring. This represented the first extended measurement of direct covariance measurements of latent heat fluxes from buoy. This research program provided the basis for extending these types of measurements to operational buoys and experimental drifting spars. For example, a joint effort between WHOI, NOAA-PMEL and NOAA-ESRL has been funded by the NOAA TPOS project has developed a DCFS that computes research quality fluxes in near realtime and telemeters them to shore. The DCFS is expected to be deployed on a subset of the next generation surface moorings as part of TPOS, which will include radiative fluxes, wave statistics and ocean currents along with more standard measurements of mean pressure, temperature, humidity, salinity and rainfall. These measurements are required to investigate the exchange of momentum, heat and mass across the coupled boundary layers with a key application being improvement of bulk turbulent flux parameterizations under all wind, sea-state and stability conditions. These bulk models find wide use in numerical modeling, in field process studies that rely on bulk fluxes from more readily available means, and in their use in global gridded air-sea flux products that combine model and satellite data. The lack of long-term, high-quality turbulent flux time series near the air-sea boundary during high wind and sea states is a long-standing and serious impediment to improved understanding of air-sea exchange. Satellite measurements of the heat and moisture fluxes have also continued to make improvements over the past few decades. Changes in evaporation and the input fields will be compared with buoys as well as closing water budgets across the basin and in more discrete areas, and the prospects of satellites providing measurement accuracies that will allow for closing the surface heat and water budgets in this region will be discussed. This talk will describe some of these advances in measurement technology used to measure air-sea fluxes over the tropical oceans, additional platforms that may provide other opportunities for making these measurements, including spar buoys and proposed “Super Sites”, and proposed satellite missions.

Presented by

Carol Anne Clayson

Institution

Woods Hole Oceanographic Institution

Keywords

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Available May 26 3-4 PM EST.

Estimating Surface Flux Bias Feedbacks to the Intra-seasonal Precipitation in the CESM2 and E3SM

Chia-Wei Hsu1, Charlotte DeMott1, Steven J. Woolnough2

Abstract

Tropical intra-seasonal (20-100 day) convection regulates weather patterns globally through extratropical teleconnections. Surface latent heat fluxes help maintain tropical intra-seasonal convection and the Madden-Julian oscillation by replenishing column water vapor lost to precipitation. Latent heat fluxes estimated using surface meteorology from moorings or satellites and the COARE3.0 bulk flux algorithm suggest that latent heat fluxes contribute 8% of the intra-seasonal precipitation anomaly over the Indian and western tropical Pacific Oceans [Dellaripa and Maloney, 2015, Bui et al., 2020].

In this study, we use in-situ data from TAO/TRITON to create a location-based latent heat flux matrix determined by specific humidity deficiency at the surface layer (dQ) and surface wind speed (sfcWind). By comparing latent heat fluxes within this matrix for observations and models/reanalysis (E3SM, CESM2, and ERA5) that typically use bulk algorithms that predate COARE3.0, we can quantify the latent heat flux biases in the model/reanalysis under different dQ and sfcWind values. The latent heat flux biases with respect to the COARE algorithm demonstrate dependence on both sfcWind and dQ. An offline latent heat flux correction based on the in-situ data is applied to model simulations based on the corresponding dQ and sfcWind values. The correction in E3SM surface fluxes leads to a statistically significant 20% reduction in the latent heat flux contribution to intra-seasonal precipitation, and brings the model estimate in better agreement with the observed contribution shown by Bui et al., [2020] over the western tropical Pacific.

Presented by

Chia-Wei Hsu <Chia-Wei.Hsu@colostate.edu>

Institution

1. Colorado State University, USA; 2. University of Reading, UK

Keywords

Latent heat bias, precipitation

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Available May 26th 15:05-16:00 US EDT

Predicting and detecting surface ocean stable layers due to rain and diurnal warming

Elizabeth J. Thompson 1, James N. Moum 2, Chris W. Fairall 1, Steven A. Rutledge 3

Abstract

Near surface stratification of the ocean by rain, river outflow, and/or solar radiation absorption limit the depth penetration of ocean mixing and amplify the surface variability of ocean temperature, salinity, and air-sea fluxes. We review results on these coupled processes from a field campaign across the equatorial central Indian Ocean: DYNAMO 2011. Determining the wind speed at which surface stable layers can form and persist appeared to be the key to predicting these features.

Diurnal warm layers (DWLs) formed by solar heating populated 30% of the data set and rain layers (RLs) populated 16%. Combined contributions from rain and insolation formed RL-DWLs in 9% of the data set. RLs were detected at values of U up to 9.8 m/s, while DWLs were only detected at U10 < 7.6 m/s (99th percentile values), symptomatic of the greater buoyancy flux provided by moderate to high rain rate compared to insolation. From the ocean friction velocity, u*w, and surface buoyancy flux, B, we derived estimates of hS', stable layer depth, and Ub', the maximum U10 for which stratification should persist at hS' for fixed B. These estimates predicted (1) 36 out of 44 observed stratification events (88% success rate) and (2) the wind limits of these events, which are considered to be the 99th percentile values of U10. This suggests a means to determine the presence of ocean stable layers at depths ≤ 5 m from surface data: U10 and B.

Near-surface stratification varied throughout two Madden-Julian Oscillation (MJO) cycles. In suppressed MJO periods, (U10 ≤ 8 m s1 with strong insolation), RLs and RL-DWLs were rare while DWLs occurred daily. During disturbed and active MJO periods, (U10 ≤ 8 m s1 with increased rain and cloudiness), multiple RLs and RL-DWLs formed per day and DWLs became less common. When westerly wind bursts occurred, (U10 = 7–17 m s1 with steady rain), RLs formed infrequently and DWLs were not detected.

Presented by

Elizabeth J. Thompson

Institution

1) NOAA Physical Sciences Laboratory, 2) Oregon State University, 3) Colorado State University

Keywords

sst, air-sea fluxes, ocean stability, rain, diurnal warm layers, air-sea interaction

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Available Wed May 26, 15:05-16:00 EDT (3:05-4:00 pm EDT)

Intraseasonal variability in precipitation and fluxes across the tropics observed by buoys and CYGNSS

Emily M. Riley Dellaripa, Eric Maloney, Hien Bui, and Bohar Singh

Abstract

This presentation will discuss the relative importance of surface latent heat fluxes (LHFLXs) to intraseasonal precipitation. Previous works that used RAMA and TAO buoy flux measurements in conjunction with TRMM rainfall to determine the relationship between intraseasonal precipitation and LHFLXs in the Indian, west Pacific, and east Pacific Oceans will be reviewed and compared to more recent analysis using LHFLXs derived from CYGNSS satellite wind speed measurements and IMERG rainfall. In general, the buoy and CYGNSS-satellite based results are consistent with each other and both show that LHFLXs have a non-negligible contribution to maintaining intraseasonal precipitation in the three regions studied (i.e., Indian, west Pacific, and east Pacific Oceans). Specifically, variability of intraseasonal LHFLXs are shown to be about 10% of intraseasonal precipitation variability, which is significant given that previous studies have shown that vertical motions associated with intraseasonal deep convection export moist static energy at a rate of about 10%-20% of precipitation variability and intraseasonal radiative anomalies are about 17% of precipitation variability.

Presented by

Emily Riley Dellaripa

Institution

Colorado State University, Colorado State University, Pusan National University, International Research Institute for Climate and Society

Keywords

Intraseasonal Oscillations, surface fluxes, buoys, CYGNSS satellite

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Available May 26th 15:15 - 16:00 EDT

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Connecting the thermocline with the surface in the eastern equatorial Pacific

Frank Bryan, Billy Kessler, Anna-Lena Deppenmeier, Luanne Thompson

Abstract

Upwelling is key in regulating SST in the eastern equatorial Pacific. Most previous observational estimates of upwelling have been made by integrating over large control volumes (typically 5 deg S to 5 deg N) and are unable to constrain the latitudinal distribution of upwelling within the cold-tongue. Using high-resolution ocean models we describe the detailed spatial structure of upper ocean divergence and upwelling and their partition into geostrophic and ageostrophic components, along with implications for observing system needs.

Presented by

Frank Bryan

Institution

National Center for Atmospheric Research, NOAA Pacific Marine Environmental Laboratory, University of Washington/School of Oceanography

Keywords

Upwelling, transport, PUMP, ocean models

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Available May 26 13:00-14:15 MDT (15:00-16:15 EDT), other times May 24-26 possible by e-mail request

Sea Surface Salinity Short Term Variability in the Tropics from Mooring Data

Bingham, Frederick M. and Susannah Brodnitz

Abstract

Using data from the Global Tropical Moored Buoy Array we study the validation process for satellite measurement of sea surface salinity (SSS). We compute short-term variability (STV) of SSS, variability on time scales of 5-14 days. It is meant to be a proxy for subfootprint variability as seen by a satellite measuring SSS. We also compute representation error, which is meant to mimic the SSS satellite validation process where footprint averages are compared to pointwise in situ values. We present maps of median values of these quantities over the tropical array. We also look at seasonality in the variability of SSS and find which months have maximum and minimum amounts. STV is driven at least partly by rainfall. Moorings exhibit larger STV during rainy periods than non-rainy ones.

Presented by

Frederick Bingham

Institution

University of North Carolina Wilmington, Center for Marine Science

Keywords

sea surface salinity, remote sensing, variability, representation error

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Available 26 May 3:10-3:40 pm EDT

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Tropical Pacific Air-Sea Interaction: Processes and Biases Relevant to ENSO and Strong Wind Events

Ho-Hsuan Wei (1), Aneesh Subramanian (1), Kristopher Karnauskas (2), Charlotte DeMott (3), Matthew Mazloff (4), Magdalena Balmaseda (5), Frederic Vitart (5), and Beena Sarojini (5)

Abstract

Oceanic and atmospheric variability in the eastern edge of Indo/western Pacific Warm Pool and associated oceanic subsurface features are essential for air-sea interactions involved in ENSO and MJO dynamics. In this study, we seek to determine the physical mechanisms governing air-sea interactions in the region, and thus the impacts of model biases under different timescales. We use the Ocean ReAnalysis System 5 (ORAS5) to identify mean-state biases in the NCAR Community Earth System Model version 2 (CESM2) with a particular focus on upper ocean properties and air-sea interaction processes, and show that the CESM2 has warm and fresh surface biases in the tropical Pacific Ocean, a barrier layer that is too thin in the western Pacific, and an isothermal layer depth that is too deep in the eastern Pacific, which impact air-sea interaction processes involved in ENSO development. For shorter timescales, the MJO is a dominant mode of intraseasonal variability in the tropics. We analyze the subseasonal forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) where the ocean states were initialized using different Observation Sensitivity Experiment analyses. We examine the influence of the subsurface ocean features on the development of biases and how they would respond differently to the atmospheric systems through air-sea interaction processes. Based on these results, we emphasize how variability and model biases in surface and subsurface ocean features influence the air-sea interaction processes and therefore the evolution and prediction of ENSO and MJO in the tropical Pacific region.

Presented by

Ho-Hsuan Wei

Institution

(1) CU Boulder, (2) CU Boulder/CIRES, (3) CSU, (4) UCSD, (5)ECMWF

Keywords

barrier layer, subsurface ocean structure, ENSO, ECMWF OSE experiment, subseasonal forecast, strong wind event

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Available May 26th from 3:05 - 4:00 PM EDT

Atmospheric response to abrupt ocean fronts from Saildrone direct covariance measurements

Jack Reeves Eyre, Meghan Cronin, Dongxiao Zhang

Abstract

In the eastern and central tropical Pacific, a strong front exists between the cold tongue of upwelled water on the equator and warmer water to the north. Over the equatorial cold tongue, the atmospheric boundary layer tends to be stabilized and winds are weak; while over the “thermal equator” to the north, winds tend to converge into an Intertropical Convergence Zone (ITCZ). It is well established that ocean mesoscale gradients have a significant influence on the atmosphere, but the effect of submesoscale ocean variability on the atmosphere is not well understood. In this study, we use direct covariance wind stress and other measurements collected by Saildrone uncrewed surface vehicles to explore the near-surface atmospheric response to abrupt submesoscale gradients within the larger scale ocean front. Surface fluxes are assessed with both direct covariance and bulk methods, and the comparison between the two methods tells us about the validity of the theory behind bulk methods in the presence of submesoscale variability. Our results can help ascertain whether current model coupling methods (bulk algorithms) and forcing datasets are suitable as models are increasingly able to resolve the ocean submesoscale.

Presented by

Jack Reeves Eyre

Institution

Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington; NOAA Pacific Marine Environmental Laboratory

Keywords

ocean-atmosphere interaction, surface fluxes, submesoscale, Saildrone

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Available 26 May, 2021 -- 15:05 to 16:05 Eastern Daylight Time (EDT)

NCAR’s Integrated Surface Flux System (ISFS): A campaign driven micronet supporting atmospheric boundary layer research

Jacquie Witte, Steve Oncley, Kurt Knudson, Dan Buonome, Isabel Suhr, Matthew Paulus, Chris Roden

Abstract

ISFS supports field campaigns designed to study energy fluxes, ecosystem responses to meteorological drivers, and coupling between land and ocean surfaces and the atmosphere. Variables often measured or derived include momentum fluxes, sensible and latent heat fluxes, short- and long-wave radiation, CO2/H2O fluxes, as well as P-T-U and wind measurements. Each ISFS micronet is tailored and structured around diverse ecosystems and deployments can be scaled up from a single site of an array of towers to address fine-scale atmospheric turbulence to a network of high-density eddy covariance flux towers that can support regional scale modeling and various process studies. An overview of the ISFS sensor suite, data ingest system, and archival display will be presented. We illustrate ISFS capabilities and the challenges faced by highlighting various deployments over the years as examples. By sharing the ISFS perspective on what it takes to maintain atmospheric flux systems in heterogeneous, foreign and challenging landscapes, we hope to contribute to the discussion on community needs for observational networks.

ISFS URL: https://www.eol.ucar.edu/observing_facilities/isfs

ISS (Integrated Sounding System) URL: https://www.eol.ucar.edu/observing_facilities/iss

Dropsondes URL: https://www.eol.ucar.edu/node/10082

Presented by

Jacquie Witte <jwitte@ucar.edu>

Institution

NCAR/Earth Observing Laboratory

Keywords

atmosphere, boundary layer, fluxes, momentum, h2o, co2, winds, surface meteorology

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Available May 26, 15:00 - 16:00 EDT

Diurnal Cycle of Air-Sea Interactions in Frontal Regions

Meghan F. Cronin^1, Dongxiao Zhang^2, Jack Reeves Eyre^2, and Samantha Wills^2

Abstract

In regions of high insolation and low winds, diurnal warming of the ocean surface can lead to an increase in sea surface temperature (SST) of several degrees Celsius, and a temperature stratification that extends through the top few meters of the ocean. There is growing understanding that resolving this diurnal warming is necessary for numerical coupled atmosphere-ocean systems. In this presentation, we use the Fairall et al. (1996) modified 1-dimensional mixed layer model to help distinguish SST anomalies associated with diurnal warming from those associated with fronts. This decomposition is particularly useful for observations from mobile platforms that sample both temporal and spatial variability, such as Saildrone, a new, wind- and solar-powered uncrewed surface vehicle. Using high resolution air-sea interaction observations from three Saildrone missions to the eastern and central tropical Pacific, we show that SST fronts that destabilize the atmospheric boundary layer, also tend to destabilize the oceanic boundary layer. As a consequence, the amplitude of the SST diurnal cycle is reduced in these frontal regions. Implications about frontal air-sea interaction and the need of Tropical Pacific Observing System to resolve SST fronts and high frequency variability will be discussed.

Presented by

Meghan Cronin

Institution

1. NOAA Pacific Marine Environmental Labatory, Seattle WA; 2. University of Washington, The Cooperative Institute for Climate, Ocean, and Ecosystem Studies, Seattle, WA

Keywords

Saildrone, diurnal cycle, fronts

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Available 25 May 2021 15:05-15:35 EDT

Small-scale variations in wave slope and momentum flux from wave-current interactions

Suneil Iyer, Jim Thomson, Kyla Drushka, Elizabeth Thompson

Abstract

Wave-current interactions influence wave slope, surface roughness, and momentum flux when the surface current direction is strongly aligned with the wave direction. This process, which results from a Doppler shift, has been observed in the field in coastal areas where surface currents are highly variable but not in the open ocean where currents are less variable. We used observations from six SWIFT drifters and two Wave Gliders, deployed as part of the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) in early 2020, to investigate wave-current interactions in an area of moderate mesoscale activity in the open ocean. Wave mean square slopes are calculated from wave spectra and are positively correlated with wind speed. At wind speeds between 4 and 12 m/s, wave slopes are elevated by approximately 10% when surface currents are strongly aligned with waves compared to when currents are weak or opposed waves. Because wave slope is proportional to surface roughness and air-sea momentum flux, these findings suggest that significant spatial variations in air-sea momentum flux exist in areas of stronger mesoscale currents. Heat and vapor fluxes will also be affected. This highlights a need for wave and surface current measurements in future observational studies of air-sea interactions in the open ocean in addition to coastal areas. Collocated wave, flux, and current observations would provide additional insight into the mechanisms driving air-sea fluxes, mixing, and turbulence on both sides of the air-sea interface, beyond what is modeled currently from bulk algorithms. Our work may also be of importance for modeling studies because wave-current-flux interactions are not comprehensively parameterized in the current version of the COARE bulk flux algorithm. Results and data from this study could potentially be used in the development of more fully coupled atmosphere-ocean-wave models.

Presented by

Suneil Iyer

Institution

Applied Physics Laboratory, University of Washington

Keywords

air-sea interactions, momentum flux, waves, surface currents

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Available May 26th 15:05 to 16:05 EDT