WCRP-CLIVAR Workshop on Climate Interactions among the Tropical Basins

UCAR

2021 WCRP-CLIVAR Workshop on Climate Interactions among the Tropical Basins

More info: https://www.clivar.org/events/wcrp-clivar-workshop-climate-interactions-among-tropical-basins-online

Filter displayed posters (134 keywords)

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Show Posters: with Video Chat with Recorded Presentation

Tracks

February 24th Session 1 (13)

February 24th Session 2 (10)

February 25th Session 1 (14)

February 25th Session 2 (16)

▼ February 24th Session 1 Back to top

Atlantic Zonal Mode: An emerging source of Indian summer monsoon variability in a warming world

C. T. Sabeerali, R. S. Ajayamohan, Hamza Kunhu Bangalath and Nan Chen

Abstract

Atlantic Zonal Mode (ZM) and Indian summer monsoon rainfall (ISMR) are known to have an inverse relationship, which means that the cold (warm) phases of AZM result in strong (weak) ISMR. Here, we report that the inverse relationship between AZM and ISMR has significantly strengthened in recent decades. We find a robust increase in interannual variability of sea surface temperature over the eastern tropical Atlantic Ocean in recent decades, which implies an increase in the number of strong AZM events toward the end of the twentieth century. The increase in strong AZM events alters the large‐scale monsoon circulation by enhancing the Kelvin wave response into the Indian Ocean, leading to an enhanced AZM‐ISMR teleconnection. This demands a better representation of the AZM‐ISMR teleconnection in climate models for improving seasonal monsoon prediction in a warming world.

Presented by

Ajaya Mohan Ravindran

Institution

New York University Abu Dhabi United Arab Emirates

Keywords

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El Niño impact on northwest African upwelling

Jorge Lopez-Parages, M. Wade, B Rodríguez-Fonseca, P.A. Auger, L. Terray, M. Martín-Rey, N. Keenlyside, C. Gaetan, A. Rubino, M.W. Arisido, A. Lazar, A.T. Gaye, and T. Brochier

Abstract

One of the most robust ENSO teleconnections is that linking SST anomalies in the equatorial Pacific and Tropical North Atlantic (TNA) in boreal spring. While the role played by the wind-evaporation- SST (WES) feedback in maintaining the ENSO-related SST anomalies over the TNA is well understood, many questions remain open about the signature of this ENSO teleconnection on the northwest African upwelling system and its role for the further response during the spring season along the whole TNA. This issue is analyzed here in both observations and CGCM models with different nominal resolution (CMIP6 HighResMIP simulations). In particular, the relevance of the mean state variability in the tropical Atlantic for modulating the northwest African upwelling response to ENSO has been assessed in depth. Furthermore, and considering the exceptional ecological importance of this upwelling area, the ENSO-related influence on the spatio-temporal variability of round sardinella (the dominant fish species in terms of abundance) has been also analyzed. To this aim, an end-to-end strategy which combines models of physics (hydrodynamic), lower trophic levels (nutrient-plankton) and upper trophic levels (sardinella), is used. All these analyses highlight from both climate and ecological perspectives, the relevance of better understanding the ENSO-northwest African upwelling teleconnection.

Presented by

Jorge López Parages

Institution

UCM, GBU, IRD, CERFACS, LOCEAN, UniVe, UiB

Keywords

ENSO, Canary Upwelling System, GCMs, Nominal resolution, Sardinella

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Available February 24th, 15-16 (UTC)

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El Niño-Southern Oscillation Evolution Modulated by Atlantic Forcing

Yoshimitsu Chikamoto, Z. F. Johnson, S.-Y. Simon Wang, M. J. McPhaden & T. Mochizuki

Abstract

The El Niño-Southern Oscillation (ENSO) exerts a strong influence on tropical Atlantic variability, but it is also affected by Atlantic forcing. Previous research has proposed three Atlantic precursors for ENSO: the North tropical Atlantic, the equatorial Atlantic, and the entire tropical Atlantic. However, the relative importance of these Atlantic precursors for ENSO remains unclear. Here, we present evidence from a set of multi-model partial ocean assimilation experiments that equatorial Atlantic cooling is the main contributor for weakening equatorial zonal winds in the Indo-Pacific sector and subsequent ocean warming in the tropical Pacific. Opposite tendencies occur for a warmer equatorial Atlantic. The equatorial Atlantic affects the inter-basin climate seesaw between the Atlantic and Pacific through an atmospheric zonal Wavenumber 1 pattern. However, model mean state biases and systematic errors prevent a precise assessment of the response times for the equatorial Pacific trade winds to Atlantic forcing.

Presented by

Yoshimitsu Chikamoto

Institution

Utah State University

Keywords

ENSO, interbasin interaction, Atlantic remote impact, partial ocean assimilation

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Available February 24 at 15h-16h UTC

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Importance of Central American Orography on Tropical Pacific Climate and Inter-Basin Interactions

Alyssa Atwood, Jane Baldwin, David Battisti, Gabe Vecchi

Abstract

The narrow Sierra Madre mountain range that extends across Central America plays an outsized role in setting the background climatology of the tropical Pacific and amplifying the seasonal characteristics of the El Niño/Southern Oscillation, by blocking the low-level easterly trade winds that flow from the tropical Atlantic to Pacific basins. Orographic height biases in this mountain range are typically large in Earth system models, with implications for their fidelity in representing inter-basin climate interactions under past and future climate change. We demonstrate the severity of these biases and discuss the consequences in representing the inter-basin connectivity between the tropical Atlantic and Pacific during a meltwater-induced collapse of the Atlantic thermohaline circulation. We present a physically based and computationally computationally inexpensive method that can significantly improve the model biases.

Presented by

Alyssa Atwood

Institution

Florida State University

Keywords

tropical Pacific, ITCZ, Sierra Madres, ENSO, Atlantic thermohaline circulation

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Available February 24th, 15-16pm UTC

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Indian Ocean as mediator of ENSO teleconnections during boreal Winter

Muhammad Adnan Abid

Abstract

El Niño-Southern Oscillation (ENSO) teleconnections modulate the seasonal mean circulation anomalies across the globe during the boreal winter season, but these teleconnections may exhibit intra-seasonal variations, which is discussed in this study using reanalysis and models. During early winter, the warm ENSO phase favours a precipitation dipole in the Indian Ocean through an atmospheric teleconnection, where positive anomalies are present in the western and negative anomalies appear over the eastern Indian Ocean. This western-eastern Indian Ocean precipitation dipole is named as the Tropical western-eastern Indian Ocean (TWEIO) dipole. The ENSO-Indian Ocean connection are strong in early winter and weaken in late winter. In early winter a warm ENSO through TWEIO dipole modulates the subtropical South Asian jet, which acts as a Rossby wave source for a positive North Atlantic Oscillation (NAO) response in the North Atlantic European (NAE) region. Moreover, the Indian Ocean also mediates the ENSO teleconnections with winter precipitation over the Central Southwest Asian region. The Indian Ocean heating dipole is partly enforced by the ENSO but can also exist independently. This observed intra-seasonality of the ENSO teleconnections is well captured by ECMWF-SEAS5 predictions and the CMIP5 models. Idealized Atmospheric General Circulation Model (AGCM) numerical experiments forced with an Indian Ocean heating dipole anomaly support this hypothesis. Thus, the inter-basin interactions seem to be a key to improve our understanding of ENSO teleconnections, which can be revisited globally in this framework.

Presented by

Muhammad Adnan Abid

Institution

Abdus Salam International Center for Theoretical Physics (ICTP), Trieste, Italy

Keywords

ENSO, Indian Ocean, Teleconnections

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Available February 24, 2021; 16-17h CEST (15-16h UTC)

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Inferring causes for Multidecadal Variability of tropical interbasin connections

Belen Rodriguez-Fonseca, Verónica Martín

Abstract

Tropical interbasin connections have been found to occur in observations during determinant periods. On the one hand, Indian ocean is connected with north tropical Atlantic and equatorial Pacific in periods in which central Pacific Niños configuration prevail. On the other hand, Indian ocean dipole is connected to Equatorial Atlantic and Pacific in a periods in which eastern Pacific Niños dominate. Finally, there are other periods in which each tropical basin presents internal modes of variability with no influence from the adjacent oceans. In this work we try to inferr causes for multidecadal modulations of tropical basin interanual variability using observations and models. Different metrics are used and the interanual variability together with the background state conditions are analysed in order to provide a cogent view of tropical interbasin connections

Presented by

Belen Rodriguez-Fonseca

Institution

Universidad Complutense de Madrid

Keywords

CMIP6 tropical interbasin connections

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Available wednesday 24 of February 15 pm UTC to 17 pm UTC

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Influences of Atlantic zonal mode on Atlantic tropical storm activity and its roles in ENSO-Atlantic tropical storm relationship

Dongmin Kim1,2, Sang-Ki Lee2, Hosmay Lopez2, Gregory Foltz2 and Caihong Wen3

Abstract

Atlantic tropical cyclones (TC) and their associated severe storm surge and coastal flooding caused loss of human lives and damage to properties. It is well known that the seasonal activity of Atlantic TC is largely modulated by tropical Pacific and Atlantic sea surface temperature anomalies (SSTAs) associated with El Niño-Southern Oscillation (ENSO) and Atlantic meridional mode (AMM). However, ENSO is typically in a developing phase during the peak season of the Atlantic hurricane (August–October), and AMM usually develops in boreal spring and often dissipates before August. In the tropical Atlantic, the leading mode of SST variability in boreal summer and fall is Atlantic Niño/Niña, characterized by warm/cold SSTAs in the eastern equatorial Atlantic that often persists through the Atlantic hurricane peak season. Nevertheless, the relationship between Atlantic Niño/Niña and Atlantic TC activity has not yet been explored. This is the first systematic study of the physical and statistical links between Atlantic Niño/Niña and Atlantic TC. Our analysis of observational and reanalysis datasets during 1948-2019, together with model experiments, shows that Atlantic Niño strengthens the Atlantic intertropical convergence zone, increasing rainfall over the west African sub-Sahel region and African easterly waves. Additionally, the enhanced atmospheric convection produces low-level westerly wind anomalies over the tropical North Atlantic, which in turn increases low-level relative vorticity and decreases vertical wind shear over the Atlantic TC main development region (MDR). These atmospheric conditions over the MDR are favorable for increasing Atlantic TC activity. Further analysis shows that the tendency for La Niña to enhance Atlantic TC activity is amplified during Atlantic Niña and weakened during Atlantic Niño. Conversely, unfavorable conditions for Atlantic TC activity during El Niño are amplified during Atlantic Niña but suppressed during Atlantic Niño. This study suggests that Atlantic Niño/Niña may aid to improve the current seasonal prediction skill of Atlantic TC activity.

Presented by

Dongmin Kim

Institution

1University of Miami/CIMAS, 2NOAA/AOML, 3 NOAA/CPC

Keywords

Atlantic Nino, Hurricane, ENSO

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Available Feb. 24 15:00-16:00 UTC

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Interannual variability at southern mid-latitudes of the Indian Ocean

Motoki Nagura and Michael J. McPhaden

Abstract

This study examines interannual variability in sea surface height (SSH) at southern midlatitudes of the Indian Ocean (10°-35°S). Our focus is on the relative role of local wind forcing and remote forcing from the equatorial Pacific Ocean. We use satellite altimetry measurements, an atmospheric reanalysis and a one-dimensional wave model tuned to simulate observed SSH anomalies. The model solution is decomposed into the part driven by local winds and that driven by SSH variability radiated from the western coast of Australia. Results show that variability radiated from the Australian coast dominates interannual SSH variability in the south Indian Ocean, except in the western half of the basin at low latitudes (between 10° and 17°S), where variability driven by local winds is predominant. Variability radiated from the Australian coast is of primary importance at mid latitudes, which is due to the weakness of wind stress curl anomalies in the south Indian Ocean. Correlation analysis suggests that SSH variability along the west coast of Australia originates from that in the tropical Pacific, which is driven by equatorial Pacific winds, as is pointed out by previous studies. This result indicates that interannual variability in SSH in mid latitudes of the south Indian Ocean is mainly driven remotely by Pacific winds. The zonal gradient of SSH between the western and eastern parts of the south Indian Ocean is also dominated by variability radiated from the Australian coast, indicating that interannual variability in meridional geostrophic transport is driven by Pacific winds.

Presented by

Motoki Nagura

Institution

Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, Japan

Keywords

Sea surface height variability, south Indian Ocean, ENSO

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Available February 24 at 22h-23h UTC

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Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO

Steven C. Hardiman, Nick J. Dunstone, Adam A. Scaife, Doug M. Smith, Jeff R. Knight, Paul Davies, Martin Claus, and Richard J. Greatbatch

Abstract

Northern Europe and the UK experienced an exceptionally warm and wet winter in 2019/20, driven by an anomalously positive North Atlantic Oscillation (NAO). This positive NAO was well forecast by several seasonal forecast systems, suggesting that this winter the NAO was highly predictable at seasonal lead times. A very strong positive Indian Ocean dipole (IOD) event was also observed at the start of winter. Here we use composite analysis and model experiments, to show that the IOD was a key driver of the observed positive NAO. Using model experiments that perturb the Indian Ocean initial conditions, two teleconnection pathways of the IOD to the north Atlantic emerge: a tropospheric teleconnection pathway via a Rossby wave train travelling from the Indian Ocean over the Pacific and Atlantic, and a stratospheric teleconnection pathway via the Aleutian region and the stratospheric polar vortex. These pathways are similar to those for the El Niño Southern Oscillation link to the north Atlantic which are already well documented. The anomalies in the north Atlantic jet stream location and strength, and the associated precipitation anomalies over the UK and northern Europe, as simulated by the model IOD experiments, show remarkable agreement with those forecast and observed.

Presented by

Steven Hardiman

Institution

Met Office, Exeter, UK

Other Affiliations

College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK; GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany; Faculty of Mathematics and Natural Sciences, Kiel University, Kiel, Germany

Keywords

European winter, Indian Ocean dipole, North Atlantic oscillation, seasonal forecasting, teleconnections

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Available February 24th, 15h-16h UTC

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Skillful prediction of tropical Pacific fisheries provided by Atlantic Niños

Iñigo Gómara, Belén Rodríguez-Fonseca, Elsa Mohino, Teresa Losada, Irene Polo and Marta Coll

Abstract

Tropical Pacific upwelling-dependent ecosystems are the most productive and variable worldwide, mainly due to the influence of El Niño Southern Oscillation (ENSO). ENSO can be forecasted seasons ahead thanks to assorted climate precursors (local-Pacific processes, pantropical interactions). However, owing to observational data scarcity and bias-related issues in earth system models, little is known about the importance of these precursors for marine ecosystem prediction. With recently released reanalysis-nudged global marine ecosystem simulations, these constraints can be sidestepped, allowing full examination of tropical Pacific ecosystem predictability. By complementing historical fishing records with marine ecosystem model data, we show herein that equatorial Atlantic Sea Surface Temperatures (SSTs) constitute a superlative predictability source for tropical Pacific marine yields, which can be forecasted over large-scale areas up to 2 years in advance. A detailed physical-biological mechanism is proposed whereby Atlantic SSTs modulate upwelling of nutrient-rich waters in the tropical Pacific, leading to a bottom-up propagation of the climate-related signal across the marine food web. Our results represent historical and near-future climate conditions and provide a useful springboard for implementing a marine ecosystem prediction system in the tropical Pacific.

Presented by

Iñigo Gómara <i.gomara@ucm.es>

Institution

Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid

Other Affiliations

Instituto de Geociencias (IGEO), UCM-CSIC

Keywords

Pantropical Interactions, El Niño-Southern Oscillation, Atlantic Niños, Upwelling, Fisheries, Prediction model

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Available February 24, 2021 at 15h-16h UTC

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South Atlantic Variability and connections with El Niño Southern Oscillation

Aubains Hounsou-Gbo, Jacques Servain, Francisco das Chagas Vasconcelos Junior, Eduardo Sávio P. R. Martins and Moacyr Araújo

Abstract

Several studies have indicated a teleconnection between the boreal summer Atlantic Niño (ATL3: 3°S-3°N, 0°-20°W) and the subsequent Pacific El Niño Southern Oscillation (ENSO), when the Atlantic leads the Pacific by about 6-month. It has been shown that this teleconnection, which involves the Walker circulation, is strong during the first and last decades of the twentieth century. We show that a second Atlantic Niño in boreal fall/early winter (October-December, hereinafter called winter Atlantic Niño) is also negatively connected with the following year ENSO (Niño3: 5°S-5°N, 90°W-150°W), with a multidecadal modulation of the lead time. The nearly 1-year leading influence of the winter Atlantic Niño on ENSO is strong in the mid-twentieth century, i.e., when the summer Atlantic Niño is weakly correlated with ENSO. This connection leads to early development of ENSO and widely coincides with high persistence of the Atlantic Niño from summer to winter. On the other hand, previous studies have shown a close connection between the summer Atlantic Niño and the South Atlantic Ocean Dipole (SAOD), where the SAOD is defined as the difference of the sea surface temperature anomalies averaged within the northeastern pole (NEP: 0°-15°S, 10°E-20°W) and the southwestern pole (SWP: 25°S-45°S, 10°–60°W). Interestingly, in boreal summertime, the NEP and the SWP are significantly negatively correlated during the first and last decades of the 1905-2018 study period and weakly correlated in the mid-twentieth century. These results also indicate that the persistence of the Atlantic Niño from summer to winter should be related to the association between the NEP and the SWP in the south Atlantic Ocean. Our study suggests the relevance of the south Atlantic Ocean variability for the ENSO teleconnection and predictability.

Presented by

Aubains Hounsou-Gbo

Institution

Research Institute for Meteorology and Water Resources (FUNCEME), Fortaleza-CE, Brazil

Other Affiliations

International Chair in Mathematical Physics and Applications (ICMPA-Unesco Chair), UAC, Benin

Keywords

Atlantic equatorial mode; El Niño southern oscillation; Teleconnection; Predictability

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Available February 24th 15-16pm UTC

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The Pacific-Indian Ocean coupling and seasonal prediction of the Asian summer climate

Yu Kosaka, Yuhei Takaya, Masahiro Watanabe, Shuhei Maeda

Abstract

Widespread climate anomalies are observed in South, Southeast and East Asia in boreal summer following an El Nino event that peaked in winter. These anomalies form despite that Equatorial Pacific SST signal of El Niño has dissipated before the summer. Recent studies have identified the Indo-western Pacific Ocean capacitor (IPOC) mode which maintains itself through an inter-basin feedback between the tropical Indian Ocean and western North Pacific and through the wind-evaporation-SST (WES) feedback. Those feedbacks enable the IPOC mode to emerge without specific external forcing, but in reality, decaying ENSO is its major driver. Our hindcast experiment with the operational coupled prediction system at the Meteorological Research Institute of Japan Meteorological Agency shows that the IPOC mode, together with concurrent ENSO, enables seasonal prediction for summer Asian climate. Hindcasts initialized in May show a high skill in predicting Asian climate in subsequent boreal summer. The prediction skill of precipitation and land surface temperature arises from successful prediction of the anomalous surface anticyclone extending from the tropical western North Pacific to the Bay of Bengal in post-El Niño summer and the associated Pacific-Japan teleconnection pattern into the midlatitude western North Pacific. Furthermore, the model successfully reproduces summer tropical cyclone activity over the western North Pacific. Process understanding on the origin of predictability provides basis toward the operational seasonal predictions.

Presented by

Yu Kosaka

Institution

Research Institute for Advanced Science and Technology, the University of Tokyo

Keywords

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Untangling the Mechanisms of Indian Ocean Dipole Variability

Sarah Larson, Sang-Ki Lee, Nat Johnson

Abstract

Identifying the relative importance of ENSO, wind-driven ocean dynamics, and thermodynamics in driving Indian Ocean Dipole (IOD) variations is crucial to better understanding IOD evolution, seasonality, predictability, and impacts. While thermodynamics likely play a secondary or insubstantial role, ENSO and wind-driven ocean dynamics are both known to drive IOD variability. However, disentangling these two forcing types from each other is nearly impossible, as winds linked to equatorial Pacific variability are known to modulate upwelling in the equatorial Indian Ocean, driving IOD variability. Data analysis approaches, while informative, cannot ensure all ENSO influences are absent for a variety of reasons and pacemaker and slab ocean model experiments lack realism and consistent air-sea thermal fluxes. To eliminate these caveats, our recent work employs a process-based coupled model hierarchy to quantify the relative contribution of different IOD forcing and determine how the inclusion of each type of forcing modifies the seasonality, evolution, amplitude, and impacts of the IOD. The experiments include 1) a fully coupled model in which all IOD forcings are active, 2) a fully coupled model in which ENSO variability is absent but all other sources of IOD variability are active, and 3) a coupled model in which IOD variations can only be thermodynamically driven but ocean dynamics can modify the amplitude through mean advection and other processes. We show that all three forcing types can drive IOD variability but the characteristics, including precipitation signals, differ in a variety of ways. We also quantify the percentage of IOD events in our model that are driven by ENSO versus those definitely driven by ocean dynamics unrelated to ENSO and those driven by air-sea heat fluxes.

Presented by

Sarah Larson

Institution

North Carolina State University

Keywords

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▼ February 24th Session 2 Back to top

Decadal Modulations of ENSO Complexities by Inter-basin Interactions

Jin-Yi Yu

Abstract

Most previous studies have emphasized processes within the tropical Pacific for the generation of El Niño. We show that after a change in the phase (from negative to positive) of the Atlantic Multi-decadal Oscillation (AMO) in the early 1990s, the Atlantic Ocean has become more capable of influencing El Niño-Southern Oscillation (ENSO) dynamics. Because of these stronger Pacific-Atlantic interactions, ENSO has become more controlled by subtropical Pacific ENSO dynamics and has changed from being predominantly of the Eastern Pacific (EP) type to being predominantly of the Central Pacific (CP) type. The stronger Pacific-Atlantic interactions have also caused ENSO to become more biennial. Using observational analyses and climate models experiments, the sequence of physical processes involved in this interaction will be described. We also show that the shift to the CP ENSO has altered Pacific-Indian ocean interactions during ENSO. The Indian Ocean has become less influenced by ENSO activities. This more independent Indian Ocean enables ENSO to evolve more frequently in a multi-year pattern. More multi-year El Nino events can occur as a result. In summary, decadal changes in the interactions between the Pacific Ocean and Atlantic and Indian Oceans can give rise to changes in ENSO type, frequency, and evolution patterns. A dynamical framework is presented in the talk to suggest how inter-basin interactions can be integrated with subtropical Pacific ENSO dynamics to explain ENSO complexities.

Presented by

Jin-Yi Yu

Institution

University of California, Irvine

Keywords

AMO, Central Pacific ENSO, multi-year ENSO, ENSO diversity, ENSO evolution complexity

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Available Feb 24, 2021 22:00-23:00 UTC

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Delayed impact of Indian Ocean warming on the East Asian climate in boreal summer

Sunyong Kim and Jong-Seong Kug

Abstract

A significant negative relationship is found between the NIO SST and East Asian surface temperature anomalies in boreal summer. However, the relationship is different for individual month, showing a time-lagged relation rather than a simultaneous one. The NIO warming in June is responsible for cold anomalies over the Korea-Japan region that peak in July with a 1-month leading role. The SST increase is closely associated with enhanced convective activity in the region in June, but the relationship between SST and resultant precipitation is substantially weakened afterwards. This dependency of the precipitation sensitivity to SST anomaly is related to the climatological evolution of SST. The relatively low background SST due to the strengthening of monsoons in the late summer can weaken the sensitivity of the precipitation to SST anomaly, yet the background SST in June is strong enough to maintain an increased sensitivity of precipitation. Thus, the Indian Ocean warming in June effectively drives atmospheric Kelvin waves that propagate into the equatorial western Pacific. In the WNP, the resultant Kelvin wave-induced Ekman divergence triggers suppressed convection and anticyclonic anomalies. The WNP anticyclonic anomalies move slowly northeastward until they are located near 20°N through the local air-sea interaction, and act as a source of the Pacific-Japan teleconnection. This teleconnection pathway brings cold anomalies to the Korea-Japan region due to the cyclonic circulation that cause the radiative and horizontal advections. The overall mechanism of Indian Ocean-East Asian teleconnection is existed in July 2020.

Presented by

Sunyong Kim

Institution

Pohang University of Science and Technology, Division of Environmental Science and Engineering

Keywords

Indian Ocean, East Asian summer climate, teleconnection

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Available February 24th 22-23pm UTC

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Exploring the impact of Tropical Atlantic SST variability on Pacific decadal variability since the 1960

Giovanni Liguori, Shayne McGregor, Julie Arblaster, and Martin Singh

Abstract

Recent modelling studies have suggested that Multidecadal Tropical Atlantic variability affects the Indo-Pacific climate and played a key role during the recent hiatus in global surface warming.

While these modelling results are consistent with physically-grounded dynamics involving changes in the Walker cell circulation, the sensitivity to the specific modelling configurations and the model dependency of the results have not been fully addressed.

Here we use a suite of experiments with the Australian Community Climate and Earth-System Simulator (ACCESS) version 1.0., to provide an independent assessment of the impact that Tropical Atlantic variability has had since 1960 on Pacific climate shifts associate with variability in the Interdecadal Pacific Oscillation mode. The sensitivity to specific modelling configurations is also explored.

Presented by

Giovanni Liguori

Institution

Monash University

Other Affiliations

ARC Centre of Excellence for Climate Extremes

Keywords

Pacific Decadal Variability, SST pacemaker, IPO

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Available 21:00-23:00 UTC during poster session 2

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Impact of the model mean SST biases on the Atlantic-Pacific teleconnection

Chen Li, Dietmar Dommenget, Shayne McGregor

Abstract

In this study we addressed the important role of model background SST biases in representing the Atlantic-Pacific teleconnection, while noting the failure of climate models to reproduce the Pacific cooling trend in recent decades may partly be due to the underrepresentation of trans-basin teleconnections. Our targeted model simulation results suggest the magnitude of Pacific cooling response to a fixed Atlantic forcing is significantly reduced when background SSTs in either the Pacific or Atlantic region are nudged towards the biased CMIP5-like mean state, relative to the observed climatology simulation. Especially, when combined, the Pacific and Atlantic SST biases led to Pacific cooling response that is almost non-existent (reduced about 89%). Future efforts aim at reducing the model mean SST biases may significantly help to improve simulation skills of the trans-basin teleconnections.

Presented by

Chen Li

Institution

ARC Centre of Excellence for Climate Extremes, Monash University

Keywords

Atlantic-Pacific teleconnection; model mean state biases

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Available 24 Feb 22:00-23:00 UTC

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Indian Ocean warming can strengthen the Atlantic meridional overturning circulation

Shineng Hu, Alexey Fedorov

Abstract

The slowdown of the Atlantic meridional overturning circulation (AMOC) and the accelerated warming of the tropical Indian Ocean (TIO) are two robust features projected for anthropogenic greenhouse warming, affecting both regional and global climates. Here we use coupled climate simulations to investigate a previously overlooked link between the two phenomena. We demonstrate that TIO warming reduces rainfall over the tropical Atlantic by strengthening the Walker circulation and increasing atmospheric vertical stability. The resultant ocean salinity increase intensifies the AMOC as salinity anomalies are advected to northern high latitudes. Additionally, TIO warming enhances westerly winds over the subpolar North Atlantic, which helps maintain the stronger AMOC. A TIO warming of 0.1°C above the mean warming of tropical oceans intensifies the AMOC by ~1 Sv, leading to a stronger interhemispheric asymmetry and a northward shifted Intertropical convergence zone (ITCZ). Thus, TIO warming could delay the AMOC weakening under greenhouse warming. Indeed, we find that the AMOC weakens more strongly or completely collapses if we suppress TIO warming under doubled and quadrupled CO2 scenarios. Simulations replicating the observed tropical ocean warming further confirm this TIO-AMOC link, suggesting that the observed TIO warming might be already playing a role in sustaining the AMOC.

Presented by

Shineng Hu

Institution

Columbia University

Other Affiliations

Duke University, Yale University, Sorbonne University

Keywords

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Available Feb. 24 22:00-23:00 UTC

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Oceanic Inter-basin Interactions between the Tropical Pacific and Indian Oceans: long time scale changes

Janet Sprintall (1), Caroline Ummenhofer (2) , Shijian Hu(3)

Abstract

The Indonesian seas provide the only tropical oceanic pathway in the world connecting two major ocean basins – the Pacific and the Indian Oceans. This maritime continent that straddles the Indo-Pacific warm, fresh pool plays a pivotal role in the coupled ocean and climate system. On annual and longer time scales, the Indonesian Throughflow (ITF) is regulated by the interocean pressure difference resulting primarily from the trade winds over the western Pacific and the monsoon winds over the Indian. Recent multi-decadal changes in the wind and the buoyancy forcing over the tropical Indo-Pacific have directly affected the vertical profile, strength and the heat and freshwater transports of the ITF. These changes have influenced the large-scale sea-level, SST, precipitation and wind patterns of both the Indian and Pacific Ocean basins. Drawing primarily on the limited observational perspective, I will provide an overview of these changes in the Indo-Pacific region and where possible identify their causes, and then highlight the outstanding challenges with suggested recommendations for addressing them.

Presented by

Janet Sprintall

Institution

(1) Scripps Institution of Oceanography, (2) Woods Hole Oceanographic Institution, (3) Institute of Oceanology Chinese Academy of Sciences

Keywords

Indonesian Throughflow, interannual variability, decadal variability

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Pacific decadal oscillation remotely forced by the equatorial Pacific and Atlantic Oceans

Zachary F. Johnson, Yoshimitsu Chikamoto, S.-Y. Simon Wang, Michael J. McPhaden & Takashi Mochizuki

Abstract

The Pacific Decadal Oscillation (PDO), the leading mode of Pacific decadal sea surface temperature variability, arises mainly from combinations of regional air-sea interaction within the North Pacific Ocean and remote forcing, such as from the tropical Pacific and the Atlantic. Because of such a combination of mechanisms, a question remains as to how much PDO variability originates from these regions. To better understand PDO variability, the equatorial Pacific and the Atlantic impacts on the PDO are examined using several 3-dimensional partial ocean data assimilation experiments conducted with two global climate models: the CESM1.0 and MIROC3.2m. In these partial assimilation experiments, the climate models are constrained by observed temperature and salinity anomalies, one solely in the Atlantic basin and the other solely in the equatorial Pacific basin, but are allowed to evolve freely in other regions. These experiments demonstrate that, in addition to the tropical Pacific’s role in driving PDO variability, the Atlantic can affect PDO variability by modulating the tropical Pacific climate through two proposed processes. One is the equatorial pathway, in which tropical Atlantic sea surface temperature (SST) variability causes an El Niño-like SST response in the equatorial Pacific through the reorganization of the global Walker circulation. The other is the north tropical pathway, where low-frequency SST variability associated with the Atlantic Multidecadal Oscillation induces a Matsuno-Gill type atmospheric response in the tropical Atlantic-Pacific sectors north of the equator. These results provide a quantitative assessment suggesting that 12–29% of PDO variance originates from the Atlantic Ocean and 40–44% from the tropical Pacific. The remaining 27–48% of the variance is inferred to arise from other processes such as regional ocean-atmosphere interactions in the North Pacific and possibly teleconnections from the Indian Ocean.

Presented by

Zachary Johnson

Institution

Utah State University

Keywords

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Available 22:00 - 23:00 UTC Feb. 24

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The impact of ENSO, IOD, and their link on the Indonesian Throughflow in an ensemble of CMIP5 models

Agus Santoso

Abstract

The Pacific Ocean and the Indian Ocean are linked not only via the atmosphere, but also the ocean through the Indonesian archipelago, a pathway termed the Indonesian Throughflow (ITF). A better understanding of Indo-Pacific basin interaction requires efforts in investigating how climate variabilities interact between the two basins, and how they impact on the ITF, especially as the ITF forms part of the global thermohaline circulation and greatly regulates the Earth’s climate. How these processes are captured by climate models is an important research topic, given climate models are used to make future climate projections. The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are known to interact with each other, particularly through changes in the atmospheric Walker Circulation, and they both influence the ITF. Given a future projection of increased frequency of extreme ENSO and IOD events under greenhouse forcing, understanding how these interactions are represented in climate models is crucial. In this study, we examine ENSO, IOD, and their link in 20 CMIP5 models and the implications on ITF variability. It is found that the CMIP5 models overall capture ITF variability associated with ENSO and IOD, in agreement with an ocean reanalysis. Model biases in ENSO, IOD, and ENSO-IOD linkage are further shown to have notable impact on the simulated ITF variability. The changes under greenhouse warming will be discussed.

Presented by

Agus Santoso

Institution

UNSW Australia

Other Affiliations

Centre for Southern Hemisphere Oceans Research (CSHOR), CSIRO

Keywords

Indonesian Throughflow, ENSO, IOD, CMIP models

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Available February 24th, 22:00-23:00, UTC

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The role of coupled feedbacks in the decadal variability of the SH eddy-driven jet

Dongxia Yang

Abstract

Using CESM1 tropical Pacific pacemaker and Large Ensemble, Yang et al., (2020) suggested that tropical Pacific decadal oscillation (PDO) has made a major contribution to the SH summertime eddy-driven jet variations over the satellite era. However, both a strength and a weakness of the coupled pacemaker framework is that they allow coupled feedbacks in response to the region of prescribed SSTs. These inter-basin interactions, particularly between the tropical oceans, make it difficult to separate the direct atmospheric influence of the tropical Pacific SSTs. Hence an outstanding question arises: What's the role of air-sea coupling in the teleconnection between tropical Pacific SSTs and the SH mid-latitude circulation? Here we designed an uncoupled experiment named pacific-ocean-global- atmosphere (POGA) to compare with the tropical Pacific pacemaker. We found the South Pacific jet responds to the tropical Pacific SST variability via direct atmospheric processes. By contrast, the air-sea coupling is notably important for South Atlantic and Indian basin to enable its teleconnections with tropical Pacific SSTs. A potential mechanism is that the eastern tropical Pacific cooling could promote warming anomalies over the South Pacific Convective Zone (SPCZ) and the South Atlantic Convective Zone (SACZ) regions in the coupled pacemaker, which helps maintain the Pacific-South-America (PSA) Rossby wave propagation from tropical Pacific to South Atlantic basin.

Presented by

Dongxia Yang

Institution

Monash University, Melbourne, Australia

Keywords

tropical Pacific SSTA impact on the South Atlantic jet variations

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Available February 24 at 22h-23h UTC

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Vertical Structure of the Upper Indian Ocean Thermal Variability

Yuanlong Li, Weiqing Han, Jing Duan, Lei Zhang, Fan Wang

Abstract

Multi-timescale variabilities of the Indian Ocean (IO) temperature over 0-700 m are revisited from the perspective of vertical structure. Analysis of historical data for 1955-2018 identifies two dominant types of vertical structures that account for respectively 70.5% and 21.2% of the total variance on interannual-to-interdecadal timescales with the linear trend and seasonal cycle removed. The leading type manifests as vertically coherent warming/cooling with the maximal amplitude at ~100 m and exhibits evident interdecadal variations. The second type shows a vertical dipole structure between the surface (0-60 m) and subsurface (60-400 m) layers and interannual-to-decadal fluctuations. Ocean model experiments were performed to gain insights into underlying processes. The vertically coherent, basin-wide warming/cooling of the IO on interdecadal timescale is caused by changes of the Indonesian Throughflow (ITF) controlled by Pacific climate and anomalous surface heat fluxes partly originating from external forcing. Enhanced changes in the subtropical southern IO arise from positive air-sea feedback among sea surface temperature, winds, turbulent heat flux, cloud cover, and shortwave radiation. Regarding dipole-type variability, the basin-wide surface warming is induced by surface heat flux forcing, and the subsurface cooling occurs only in the eastern IO. The cooling in the southeast IO is generated by the weakened ITF, whereas that in the northeast IO is caused by equatorial easterly winds through upwelling oceanic waves. Both El Niño-Southern Oscillation (ENSO) and IO dipole (IOD) events are favorable for the generation of such vertical dipole anomalies.

Presented by

Yuanlong Li

Institution

Institute of Oceanology, Chinese Academy of Sciences

Keywords

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▼ February 25th Session 1 Back to top

An experimental protocol to examine the link between the tropical Atlantic and ENSO

Ingo Richter, Yu Kosaka, Hiroki Tokinaga, Shoichiro Kido

Abstract

The potential influence of the tropical Atlantic on the development of ENSO has received increased attention over recent years. In particular equatorial Atlantic variability (also known as the Atlantic zonal mode or AZM) has been shown to be anticorrelated with ENSO, i.e. cold AZM events in boreal summer (JJA) tend to be followed by El Niño in winter (DJF), and vice versa for warm AZM events. One problem with disentangling the two-way interaction between the equatorial Atlantic and Pacific is that both ENSO and the AZM tend to develop in boreal spring (MAM). Here we attempt to develop a set of GCM sensitivity experiments that can quantify the strength of the Atlantic-Pacific link. The starting point is a 1000-year free-running control simulation with the GFDL CM 2.1 model. From this control simulation, we pick years in which a cold AZM event in JJA is followed by an El Niño in DJF. These years serve as initial conditions for “perfect model” prediction experiments. In the control experiments, the predictions evolve freely for 12 months from January 1 of each selected year. In the second set of predictions, SSTs are gradually relaxed to climatology in the tropical Atlantic, so that the cold AZM event is suppressed. In the third set of predictions, we restore the tropical Pacific SSTs to those in the underlying 1000-year free-running simulation, so that the El Niño event is guaranteed to develop. Comparison of these three experiments yields information on the strength of the Atlantic-Pacific connection in both directions. First results of these experiments will be presented, as well as the strengths and weaknesses of the approach.

Presented by

Ingo Richter

Institution

Japan Agency for Marine-Earth Science and Technology

Keywords

ENSO, tropical Atlantic, experiment design, GCM

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Available February 25, 22h-23hUTC

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Atlantic Multidecadal Variability modulates the climate response to El Niño-Southern Oscillation

Paloma Trascasa-Castro (1), Amanda Maycock (1), Yohan Ruprich-Robert (2), Frederic Castruccio (3) and Gokhan Danabasoglu (3)

Abstract

El Niño Southern Oscillation (ENSO) is the leading mode of interannual climate variability in the tropics with global impacts on climate and populations. ENSO and its teleconnections exhibit decadal variability that may be influenced by low frequency modes in the Pacific and Atlantic oceans. These decadal variations can either mask or amplify the signal of externally forced trends in the climate system.

Here we investigate the impact of the Atlantic Multidecadal Variability (AMV) on ENSO and its climate impacts. We use ensemble experiments from the NCAR-CESM1 model in the Decadal Climate Prediction Project (DCPP) which restore North Atlantic sea surface temperatures (SST) towards observed AMV warm and cold phases. We identify ENSO events under the two AMV phases and compare their characteristics.

During El Niño events, the warm AMV phase (AMV+) strengthens the Walker circulation and shifts the area of maximum precipitation towards the western equatorial Pacific, reducing El Niño impacts and variability. The AMV modulates the amplitude of El Niño, and that triggers a precipitation response over the equatorial Pacific that is linearly related to SST changes in the Niño3.4 region.

In the case of La Niña, the AMV+ weakens the Walker circulation, leading to an eastward shift of the Walker cell and weakening the equatorial impacts and amplitude of La Niña. However, we found that changes in SSTs alone cannot explain the different precipitation responses to La Niña between AMV+ and AMV-.

A simple ENSO feedbacks analysis suggests that AMV+ conditions dampen both thermodynamic and dynamic feedbacks, which explains why the amplitude of ENSO is reduced by the AMV. Ongoing and future work will investigate the relative importance of the changes in different feedbacks.

Presented by

Paloma Trascasa-Castro

Institution

(1) University of Leeds, United Kingdom (2) Barcelona Supercomputing Center, Spain; (3) National Center for Atmospheric Research, United States

Keywords

El Niño-Southern Oscillation, Atlantic Multidecadal Variability

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Available February 25th 15h-16h UTC

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Causal interactions between tropics and mid-latitudes in reanalysis data and S2S forecasts

G. Di Capua, J.Runge, R. V. Donner, B. v.d. Hurk, A. G. Turner, R. Vellore, R. Krishnan and D. Coumou

Abstract

Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere during boreal summer. At subseasonal (weekly to monthly) time scales, the two dominant coupled modes of tropical – mid-latitude co-variability in reanalysis data sets indicate that the South Asian monsoon is linked with the mid-latitude circumglobal teleconnection pattern, while the western North Pacific summer monsoon in the tropics is linked with a wave-5 pattern centred over the North Pacific High in the mid-latitudes. Using a causal discovery algorithm, we show that these patterns reflect two-way causal interactions between the tropics and mid-latitudes and that the strength and sign of the causal links are timescale dependent. By visualizing those causal associations on a 2-dimensional map, we are able to highlight specific mid-latitude regions that are most strongly connected to tropical convection. The observed tropical-mid-latitude linkages are only mildly affected by ENSO: La Niña strengthens the South Asian monsoon generating a stronger response in the mid-latitudes, while during El Niño years the Pacific pattern is reinforced. Building upon the successful application of our methodology to reanalysis data, we finally study how the inferred causal teleconnections are represented in sub-seasonal to seasonal (S2S) prediction models and provide a process-based validation of boreal summer teleconnections. Our findings help to identify possibly under- or over-represented mechanisms in the studied models, and thereby contributes to the development of future improved sub-seasonal forecasts.

PSW for video: dicapua21

Presented by

Giorgia Di Capua

Institution

Magdeburg-Stendal Technical University

Other Affiliations

Potsdam Institute for CLimate Impact Research, IVM - VU University of Amsterdam

Keywords

ISM, causality, boreal summer

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Available February 25th 2021 at 15h-16h UTC

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Complex networks approach for detecting tropical interactions

Verónica Martín-Gómez, Belén Rodriguez-Fonseca and José María Aliganga Agomaa

Abstract

Most of the studies already existent analyze the interaction among the oceans considering couples of basins. However, there are no studies analyzing the degree of collective interaction among the three tropical oceans and its variability along time. In this study, we consider a complex network perspective to analyze the collective connectivity among the three tropical basins. To do so, we first construct a climate network considering as network’ nodes the indices that represent the variability of the SST over the tropical Pacific, the tropical north Atlantic, the equatorial Atlantic and the tropical Indian Ocean. Then, we focus on detecting synchronization periods (periods of maximum degree of collective connectivity) using the mean network distance definition. Results show that the degree of collective connectivity among the three tropical oceans present a large muti-decadal variability and that during the last century there were two synchronization periods.

Presented by

Verónica Martín-Gómez

Institution

Complutense University of Madrid

Keywords

Tropical basins collective connectivity

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Available February 25-15h-16h UTC

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Complex systems approaches for disentangling tropical climate variability across regions and timescales

Reik Donner

Abstract

Tropical climate variability exhibits complex features in time and space originating from the nonlinear interaction of different processes in the atmosphere and ocean along with other components of the Earth system that are characterized by diverse spatial and temporal scales. In such a setting, classical methods of statistical climatology may miss important information on relevant dynamical characteristics. In my poster, I summarize a few selected recent methodological developments originating from concepts of complex systems theory that have already provided new insights into different facets of tropical climate variability and its extratropical teleconnections and drivers.

Presented by

Reik Donner

Institution

Magdeburg-Stendal University of Applied Sciences, Magdeburg, Germany

Other Affiliations

Potsdam Institute for Climate Impact Research, Potsdam, Germany

Keywords

Nonlinear variability, complex systems methods, ENSO diversity, extreme events, cross-scale coupling

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Available February 25, 15:00-16:00 UTC

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

Christian Dominguez, James M. Done and Cindy L. Bruyère

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 <dosach@atmosfera.unam.mx>

Institution

Centro de Ciencias Atmosfericas, UNAM

Keywords

easterly waves, seasonal precipitation, tropical cyclone, regional model, decadal oscillation

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Available February 25th, 15:00-16:00 UTC

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Exploring the Wider Impacts of Atlantic Multidecadal Variability using Coupled Model Ensembles

Stephen Yeager, Who Kim, Gokhan Danabasoglu

Abstract

The multidecadal variability of North Atlantic sea surface temperature (SST), referred to as Atlantic Multidecadal Variability (AMV), is considered to be a key driver of low-frequency regional and global climate variability, but the relatively short observational record makes it challenging to robustly quantify AMV impacts. Coupled model pacemaker experiments, such as those promoted by the CMIP6 Decadal Climate Prediction Project (DCPP) component C protocol, have helped to advance our understanding of inter-basin AMV teleconnections. However, the imposition of AMV-related SST anomalies in such experiments could produce spurious signals insofar as the coupled dynamics that give rise to those SST anomalies are not properly represented. An alternative AMV pacemaker experimental design is presented that involves controlled forcing of the Atlantic thermohaline circulation in order to induce an AMV response via more realistic coupled ocean-atmosphere dynamics.

Presented by

Stephen Yeager <yeager@ucar.edu>

Institution

National Center for Atmospheric Research

Keywords

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Available Feb. 25 22:00-23:00 UTC

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Impact of Equatorial Atlantic Variability on ENSO Predictive Skill

Eleftheria Exarchou , Pablo Ortega, Belén Rodríıguez de Fonseca, Teresa Losada, Irene Polo Sánchez, and Chloé ́Prodhomme

Abstract

El Niño–Southern Oscillation (ENSO) is a key mode of climate variability with worldwide climate impacts. Recent studies have highlighted the impact of other tropical oceans on its variability. In particular, observations have demonstrated that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, but it is unclear how well climate models capture this teleconnection and its role in defining the seasonal predictive skill of ENSO. Here we use, for the first time, an ensemble of seasonal forecast systems to demonstrate that a better representation of equatorial Atlantic variability in summer and its lagged teleconnection mechanism with the Pacific relates to enhanced predictive capacity of autumn/winter ENSO. An additional sensitivity study further shows that correcting SST variability in equatorial Atlantic improves different aspects of forecast skill in the Tropical Pacific, boosting ENSO skill. This study thus emphasizes that new efforts to improve the representation of equatorial Atlantic variability, a region with long standing systematic model biases, can foster predictive skill in the region, the Tropical Pacific and beyond, through the global impacts of ENSO.

Presented by

Eleftheria Exarchou

Institution

Barcelona Supercomputing Centre

Other Affiliations

Departamento de Fisica de la Tierra y Astrofisica, Universidad Computense de Madrid, Madrid, Instituto de Geociencias, IGEO (CSIC-UCM),Group of Meteorology, Universitat de Barcelona (UB, NRM, Université de Toulouse, Météo-France, CNRS

Keywords

ENSO predictions, Atlantic-Pacific teleconnection, multi-model ensemble

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Available February 25 at 15h-16h UTC.

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Impacts of Atlantic Multidecadal Variability on the Tropical Pacific: a multi-model study

Yohan Ruprich-Robert

Abstract

Atlantic Multidecadal Variability (AMV) has been linked to the observed slowdown of global warming over 1998-2012 through its impact on the tropical Pacific. Given the global importance of tropical Pacific variability, better understanding this Atlantic-Pacific teleconnection is key for improving climate predictions, but the robustness and strength of this link is uncertain. Analysing a multi-model set of 23 sensitivity experiments with Coupled Global Climate Models, we find that models differ by a factor 10 in simulating the amplitude of the Equatorial Pacific cooling response to observed AMV warming. The inter-model spread is mainly driven by different amounts of moist static energy injection from the tropical Atlantic surface into the upper troposphere. We reduce this inter-model uncertainty by analytically correcting models for their mean precipitation biases and we quantify that, following an observed 0.26ºC AMV warming, the equatorial Pacific cools by 0.16ºC with an inter-model standard deviation of 0.03ºC.

Presented by

Yohan Ruprich-Robert

Institution

Barcelona Supercomputing Center

Keywords

Atlantic impacts on Pacific - decadal timescales

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Available February 25th, 3-4pm UTC

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Influence of the extra-tropical AMV on the Senegalese-Mauritanian Upwelling System

Emilia Sánchez-Gómez, Elsa Mohino Harris, Adama Sylla, Christophe Cassou and Juliette Mignot

Abstract

The eastern boundaries upwelling systems (EBUS) are associated with high level of nutrients providing major fish resources in the world. Surface alongshore winds, together with the Coriolis effect, force the offshore water transport and the divergence of the surface flow, through Ekman Transport and Ekman suction, respectively, thereby lifting nutrient-rich deep waters into the near surface layers. Climate variations can affect the dynamics and intensity of EBUS, and this could impact the economy and food resources of the surrounding countries. For this reason, it is important to understand the climate drivers of EBUS at different timescales. In the Tropical and subtropical Atlantic there are two major EBUS: Canary and Benguela systems. Recent studies have suggested that decadal ocean variability, such as the Interdecadal Pacific Variability (IPV) and the Atlantic Multidecadal Variability (AMV) could impact the climate in the Tropical Atlantic basin. However, at decadal timescales, the influence of the IPV and AMV on the Tropical Atlantic, and more specifically on the EBUS, is less understood. This is partially due to the lack of long observational records. Climate models and sensitivity experiments can be powerful tools to understand low-frequency (decadal and more) climate variability and its impacts on remote regions. In this study we investigate the impacts of the AMV on the Tropical Atlantic, with special focus on the Senegalese-Mauritanian upwelling system (SMUS). We use the CMIP6/DCPP-C experiments, consisting in large ensembles of idealized experiments in which the North Atlantic sea surface temperatures (SSTs) are relaxed towards the observed extra-tropical AMV anomalies, for both phases of the AMV. We use two models in this study : CNRM-CM6.1 and IPSL-CM6A-LR. The models response to the different phases of AMV is analysed and we show an impact of the extra-tropical AMV on the Tropical Atlantic SSTs, Azores anticyclone and ITCZ. The SMUS shows some seasonal modifications related to the AMV phases. We explore some possible mechanisms based on a simplified heat budget analysis.

Presented by

Emilia Sanchez-Gomez <sanchez@cerfacs.fr>

Institution

CERFACS/CECI, France

Other Affiliations

Universidad Complutense de Madrid (Spain), LOCEAN/CNRS (France)

Keywords

Decadal variability on upwelling system, AMV, DCPP-C experiments

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Available February 25: 15h00-16h00 UTC (16h00 - 17h00 Paris time)

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Inter-basin Connections: Lessons learnt from Near-Term Predictions

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

Abstract

We present evidence of inter-basin connections from three different experimental setups using the ECMWF seasonal forecasting system. Firstly, a set 2-year coupled forecast experiments initialized in February 2014 demonstrate that the Indian Ocean initial state influenced the ENSO evolution in year-1 (via atmospheric bridge) and year-2 ENSO predictability (via ocean tunnel). Evidence of the atmospheric bridge between Indian Ocean and other basins is also evident in seasonal attribution experiments during DJF 2019/2020, using atmospheric only experiments with perturbed SST anomalies. Finally, Observing System Experiments where in-situ observations are withheld in the production of ocean initial conditions demonstrate that the influence of the ocean observations affect the global atmospheric circulation at seasonal time scales. The implications of the results for the ocean observing systems are discussed

Presented by

Magdalena Balmaseda

Institution

ECMWF

Keywords

Subseasonal-to-Interannual, GCM experiments, Observations

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Available February 25 at 15h-16h UTC.

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Inter-basin interaction in the Indo-Pacific to determine the systematic spread of the changes in East Asian and western North Pacific summer monsoon

Ping Huang, Shijie Zhou, Gang Huang, Kaiming Hu

Abstract

With ongoing global warming, the changes in EA-WNPSM rainfall – feeding over two billion people in East Asia and the Indochina Peninsula – projected by the Coupled Model Intercomparison Project Phase 5 (CMIP5) models show remarkable and unidentified inter-model spread. Here, we reveal the leading intermodel spread of EA-WNPSM changes in 28 CMIP5 models is related to a “dry north–wet south” dipole in East Asia and a wet Indochina and WNP. This spread pattern of EA-WNPSM changes is induced by the spread of sea surface temperature changes in the equatorial western Pacific, and can be further traced back to an apparent discrepancy among the state-of-the-art models in simulating the tropical Pacific rainfall. We can constrain the EA-WNPSM rainfall changes that there should be more rainfall increase in North China and the Korean Peninsula and less increase in South China, the Indochina Peninsula and WNP, relative to previous multi-model ensemble projections.

Presented by

Ping Huang

Institution

Institute of Atmospheric Physics, Chinese Academy of Sciences, China

Keywords

Global warming, East Asian Summer monsoon, intermodel spread

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Available February 25th 15:00-16:00 UTC

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The influences of Global atmospheric oscillation on the temperature variations in the tropical Pacific, Indian, and Atlantic Oceans

Serykh I.V. and Sonechkin D.M.

Abstract

It has been investigated whether the Pacific, Indian, and Atlantic Oceans have large-scale structures of spatial and temporal variations in water temperature similar to that of the Global Atmospheric Oscillation (GAO), most recently discovered (Serykh et al., 2019). For this purpose, data on temperature distributions in the deeps of these oceans were analyzed. Variations in water temperature in the timescale range from one year to about one decade have proved to be synchronous with corresponding variations in sea surface temperature (SST) over the oceans in GAO (Serykh and Sonechkin, 2020a). Variations in water temperature in the near-equatorial zone of the Pacific Ocean at depths up to about 150 meters behave in the same way as variations in sea surface height (SSH) and SST. Water temperature variations reveal a "striped" structure at depths from 150 to about 1000 meters. Such structure is not characteristic of GAO. But the overall similarity between SST variations at GAO and water temperature variations at large depths still persists. Variations in water temperature spread from east to west along the equator. One period of this east-west spreading is that of 14 months. This makes it possible to think that this spread is controlled by Pole tides, which in turn are caused by the Chandler wobble in the Earth's pole motion. The surface North Pacific Pole tide was found previously responsible for excitation of El Niño in the Pacific Ocean (Serykh and Sonechkin, 2019). The deep Pole tides in the South Atlantic and Southern Indian Oceans appear to be the triggers of the Atlantic El Niño and the Indian Ocean Dipole (IOD) respectively. Curiously, IOD is very weakly expressed in the field of the SST in the eastern Indian Ocean. For this reason, it is doubtful that the trigger of IOD is the alternation of increases and decreases of the Trade winds over the archipelago of Indonesia. In the about 75-meter layer, IOD is seen much better. This is consistent with the assumption that the trigger of IOD is the deep Pole tide in the southern Indian Ocean. Reflected from Australia's western coasts, this tide could intensify the cold West Australian current. At the same time, the out-of-phase behavior of IOD and Pacific El Niño can be explained by the 180-degree difference in longitudes of these phenomena. Due to the general propagation of the GAO’s spatial structure from west to east, index – predictor of El Niño and La Niña is defined. The cross-wavelet analysis between both of these indices and the Oceanic Niño Index (ONI) is performed (Serykh and Sonechkin, 2020b). This analysis reveals a range of timescales within which the closest relationship between the GAO and ONI takes place. Using this relationship, it is possible to predict El Niño and La Niña with a lead-time of approximately 12 months.

References 1. Serykh I.V., Sonechkin D.M. Nonchaotic and globally synchronized short-term climatic variations and their origin // Theoretical and Applied Climatology. 2019. Vol. 137. No. 3-4. pp 2639–2656. https://doi.org/10.1007/s00704-018-02761-0. 2. Serykh I.V., Sonechkin D.M., Byshev V.I., Neiman V.G., Romanov Yu.A. Global Atmospheric Oscillation: An Integrity of ENSO and Extratropical Teleconnections // Pure and Applied Geophysics. 2019. Vol. 176. No. 8. pp 3737–3755. https://doi.org/10.1007/s00024-019-02182-8. 3. Serykh I.V., Sonechkin D.M. Interrelations between temperature variations in oceanic depths and the Global atmospheric oscillation // Pure and Applied Geophysics. 2020a. Vol. 177. No. 12. pp 5951–5967. https://doi.org/10.1007/s00024-020-02615-9. 4. Serykh I.V., Sonechkin D.M. El Niño forecasting based on the global atmospheric oscillation // International Journal of Climatology. 2020b. https://doi.org/10.1002/joc.6488.

Presented by

Ilya Serykh

Institution

Shirshov Institute of Oceanology, Russian Academy of Sciences

Keywords

Ocean - atmosphere interrelations, short-term climatic variations, Pole tide effects on climate, El Niño – Southern Oscillation, Indian Ocean Dipole.

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Available February 25 at 15h-16h UTC

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Three methods based on ocean-atmosphere general circulation models to investigate tropical basin interactions

Guillaume Gastineau

Abstract

The shortness of available observation available impedes the identification of the dominant tropical basin interactions (TBIs), which appears not robust and sensitive to the methodology used. We will illustrate here how ocean-atmosphere general circulation models can be used to identify the TBIs. The first method presented uses prescribed tropical Pacific wind stress interannual anomalies. We illustrate that, in a coupled model study based on IPSL-CM5A-LR (Gastineau et al., 2019), this successfully constrains the global surface temperature, sea level pressure, and OHC patterns associated with the interdecadal Pacific oscillation phase transition around 1998. This shows the anomalous Pacific heat uptake during the 1998-2012 hiatus period was entirely exported towards the North Pacific (similar to 50%), Indian (similar to 30%), and Southern (similar to 20%) Oceans. The redistribution of heat through the oceanic circulation then produces a dominant OHC increases in the Southern Ocean (similar to 60% of global changes) and northern Pacific (similar to 40%). The second method presented next will be based on the nudging of SST anomalies, as illustrated by preliminary results from the CMIP6 DCPP panel C simulation performed with the IPSL-CM6-LR model. The third method uses large ensembles of historical simulations with ocean-atmosphere general circulation models. The limitations linked to model biases and the poor simulation of observed climate variability will be discussed and shortly presented for each method.

Presented by

Guillaume Gastineau

Institution

Sorbonne Université, LOCEAN

Keywords

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▼ February 25th Session 2 Back to top

Atlantic and Pacific tropics connected by mutually interactive decadal-timescale processes

Gerald A. Meehl

Abstract

Decadal climate prediction presumes there are decadal timescale processes and mechanisms that, if initialized properly, provide predictive skill beyond the first year or two. Candidate mechanisms involve Pacific Decadal Variability (PDV) and Atlantic Multidecadal Variability (AMV). If one is driving the other, then a skillful prediction of decadal variability in one basin would result in skillful predictions of SST in the other basin, with resulting global-scale teleconnections that would then simplify the decadal climate prediction problem. Here we use pacemaker model configurations to show that there tends to be a weak opposite-sign PDV response in the tropical Pacific when SSTs are specified in the Atlantic. For the PDV pacemaker experiment, there is a weak same-sign response in the tropical Atlantic. Net surface heat flux in the Atlantic and ocean dynamics in the Pacific play contrasting roles in the ocean response in the respective basins. We propose a new paradigm for decadal timescale variability such that processes in the Pacific and Atlantic are sequentially interactive through the atmospheric Walker Circulation along with contributions from midlatitude teleconnections for the Atlantic response to the Pacific. Therefore, processes and mechanisms in both basins, and their interactions, must be simulated to produce credible decadal climate predictions.

Presented by

Gerald Meehl <meehl@ucar.edu>

Institution

NCAR

Keywords

trans-basin interaction, pacemaker experiments, Walker Circulation, decadal variability, Walker Circulation

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Available 3 - 4PM Mountain Time Thursday, Feb. 25

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Changes between the tropical Pacific mean state and ENSO in PMIP4 simulations of the mid-Holocene

Xiaolin Zhang1 and Bappaditya Nag2

Abstract

El Niño/Southern Oscillation (ENSO) is a coupled ocean-atmospheric phenomenon in the tropical Pacific Ocean and contributes to global climate variability on the interannual timescale. Previous studies have indicated that ENSO is tightly coupled to the tropical Pacific mean state and annual cycle. However, despite extensive research efforts, the processes that control ENSO variability on the longer-term timescales are still poorly understood. The mid-Holocene (6,000 years before the present) provides a valuable target to probe the dynamics of low-frequency ENSO modulation and assess the sensitivity of ENSO to external forcing since the ENSO variability was reduced by as much as 60% during the mid-to-late Holocene when Earth’s orbital parameters were substantially different compared to the present. Here we investigate the ENSO variability and its link to the changes of the tropical Pacific mean state using the mid-Holocene simulation from the Paleoclimate Modelling Intercomparison Project phase 4 (PMIP4). Our result shows that the ENSO variability is reduced during the mid-Holocene, and the annual cycle in ENSO variance (i.e. the so called “phase-locking” of ENSO to the annual cycle) is also reduced along with a reduction in the amplitude of the annual cycle of the cold tongue. Further analysis reveals that the changes in the annual cycle of the tropical Pacific cold tongue are mainly attributed to weaker western equatorial Pacific trade winds in early boreal spring. Anomalous westerly wind in the western tropical Pacific can excite downwelling Kelvin waves that propagate eastward, and further deepen the thermocline and weaken the ocean-atmosphere coupling, before reaching the eastern equatorial Pacific during the development season of ENSO in boreal summer. This westerly wind anomaly is jointly induced by the attenuation of the North Pacific subtropical anticyclone and the shift in the convective pattern from the eastern Indian Ocean to the western Pacific. By probing the mechanisms that lead to reduced ENSO variability in the mid-Holocene, this work will yield important insight into the linkages between the background tropical Pacific climate and ENSO, which can be used to better project future changes in the climate.

Presented by

Xiaolin Zhang

Institution

1. University of Hamburg, 2. Indian Institute of Tropical Meteorology

Keywords

Tropical Pacific mean state, Annual Cycle, ENSO, mid-Holocene, PMIP4, North Pacific Subtropical High, Westerly Wind, Downwelling Kelvin Waves

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Changes in the inter-basin interactions of the Pacific and Atlantic oceans depending on the AMO phase

Hong Jin-Sil, Sang-Wook Yeh, Young-Min Yang

Abstract

Many researchers have argued that both sea surface temperature (SST) variabilities in the Pacific and Atlantic Oceans have significant impacts on the climate and ecological systems and they interact with each other. According to previous studies, there are constructive and destructive relationships between the Atlantic Multi-decadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) with a lead-lagged time. In this study, we found that the role of the PDO on the Atlantic Ocean depends on the AMO phase. When the PDO and AMO are in-phase, the Pacific affects the Atlantic through the Walker circulation originated from the Pacific. While they are out-of-phase, the Pacific ocean is influenced by the Atlantic ocean. To confirm these results, an Atlantic pacemaker experiment was conducted using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM3). As a result, the model experiment supports the findings in the observation.

Presented by

Jin-Sil Hong <hjss1124@gmail.com>

Institution

Hanyang University/South Korea, NUIST/China

Keywords

PDO, AMO, inter-basin interaction, Indian ocean, Pacific ocean, walker circultion

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Available Feb. 24th and 25th 22-23 UTC

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Combined Effect of ENSO-Like and Atlantic Multidecadal Oscillation SSTAs on the Interannual Variability of the East Asian Winter Monsoon

Xin Hao

Abstract

Using long-term observational data and numerical model experiments, this study found that the Atlantic multidecadal oscillation (AMO) affects the influence of ENSO-like sea surface temperature anomalies (SSTAs, which contain the variability of both El Niño–Southern Oscillation and Pacific decadal oscillation) on the interannual change in the East Asian winter monsoon (EAWM). In the observations, the out-of-phase relationship between the variations in ENSO and the EAWM was significantly intensified when the AMO and ENSO-like SSTAs were in phase. Warmer-than-normal winters occurred across East Asia when the ENSO-like SSTAs and AMO were positively in phase, with a significantly weakened Siberian high and anomalous anticyclones over the western North Pacific. The opposite patterns occurred under negative in-phase conditions. In contrast, when the ENSO-like and AMO SSTAs were out of phase, the anomalies related to the EAWM tended to exhibit relatively weaker features. Numerical model experiments confirmed these observational results. When the models were perturbed with warm ENSO-like SSTAs and warm AMO SSTAs, the atmosphere showed a weakened Siberian high, strong anticyclonic anomalies over the Philippine Sea, a weakened East Asian trough, and dominant positive temperature anomalies over East Asia, implying a weaker EAWM. Reverse responses to negative in-phase temperature anomalies were observed. However, the atmospheric signals that responded to the out-of-phase conditions were less robust. This phenomenon may be attributed to the superposition of the interannual variability of the EAWM caused by ENSO-like SSTAs upon the influence of AMO on background Eurasian climate and the Walker circulation response to the heating source provided by the AMO, which induced changes in ENSO-like variability through the surface wind anomalies and modulated the anomalous anticyclone/cyclone over the Philippine Sea in warm–cold ENSO-like events.

Presented by

Xin Hao

Institution

Nanjing University for Information Science and Technology

Other Affiliations

Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences

Keywords

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Available February 25 at 15h-16h UTC

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Critical layer in the Tropical Indian Ocean and IOD –ENSO Interaction

A.B. Polonskii, A.V. Torbinskii

Abstract

The purpose of this work is to clarify the mechanisms of generation of Indian Ocean dipole (IOD) as an internal mode, which does not relate to the Pacific ENSO events. Our published results showed that such mode could be consequence of the critical layer existence in the Tropical Indian Ocean in some seasons. In this layer, the phase velocity of planetary waves is equal to the average velocity of zonal currents and generation of growing disturbances is possible. The IOD interrelation with the Pacific ENSO events can crucially depend on the type of the ENSO event, namely on the season of the ENSO event generation. Earlier we confirmed this hypothesis using different types of the historical data. In the present work, the operative re-analysis ORAS5 data of European Centre for Medium-Range Weather Forecasts (ECMWF) on potential temperature, salinity and the zonal current component for the period 1979 – 2018’s were used. It is shown that the critical layer is formed in the vicinity of 50°E and between 12 and 13°S. The reality of the obtained results is discussed using the RAMA data.

Presented by

Alexander Polonskii <apolonsky5@mail.ru>

Institution

Institute of Natural and Technical Systems, Sevastopol, Russian Federation

Keywords

Oceanology, Indian Ocean dipole, critical layer, Rossby wave

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Available February 24 at 15h-16h UTC

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Drivers of Indo-Pacific oceanic exchange through the Indonesian Throughflow since the late 1800s using coral δ18O and ocean model simulations

Sujata A. Murty1,2, Caroline C. Ummenhofer2, Markus Scheinert3, Erik Behrens4, Arne Biastoch3, Claus W. Böning3

Abstract

The Indonesian Throughflow (ITF) serves as an important oceanic teleconnection for Indo-Pacific climate, altering heat and buoyancy transport from the Pacific to the Indian Ocean. Equatorial Pacific wind forcing transmitted through the ITF impacts interannual to interdecadal Indian Ocean thermocline depth and heat content, with implications for preconditioning Indian Ocean Dipole (IOD) events. Yet the modulation of Indian Ocean thermal properties at seasonal timescales is still highly uncertain. Here we synthesize coral δ18O records, instrumental indices (Interdecadal Pacific Oscillation (IPO), Asian Monsoon), and simulated ocean variability (sea surface salinity (SSS), temperature, heat content) from state-of-the-art NEMO ocean model hindcasts to explore drivers of seasonal to multi-decadal variability. All coral sites are located within main ITF pathways and are influenced by monsoon-driven, buoyant South China Sea surface waters during boreal winter that obstruct surface ITF flow and reduce heat transport to the Indian Ocean. Makassar and Lombok Strait coral δ18O co-varies with simulated SSS and thermocline depth at the coral sites. Sensitivity experiments additionally indicate that both sites are dominantly influenced by wind variability at multi-decadal timescales, with contributions from buoyancy forcing occurring during periods of the late 20th century. Notably, the variability in these coral and model responses reveals sensitivity to phase changes in the IPO. These results collectively suggest that the paleoproxy records are capturing important features of regional hydrography and Indo-Pacific exchange. Such proxy-model comparison is critical for understanding the drivers of variability related to changes in ITF oceanic teleconnections over the 19th and 20th centuries.

Presented by

Sujata Murty

Institution

1Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, NY, USA; 2Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Other Affiliations

3GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany ;4National Institute of Water and Atmospheric Research, Wellington, New Zealand

Keywords

coral, d18O, paleoclimate, marine geochemistry, ocean model simluations, proxy-model synthesis

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Available Feb. 25, 22:00-23:00 UTC

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How to utilize deep learning to understand climate dynamics : An ENSO example

Na-Yeon Shin, Jong-Seong Kug

Abstract

The combination of deep learning and meteorology is no longer state-of-the-art research. Many deep learning technologies have been applied, including weather forecast, climate prediction, parameterization, and resolution improvements, etc. Nonetheless, it is an issue because the dynamical interpretation through deep learning is still insufficient. Therefore, we would like to present a novel perspective on climate interpretation through deep learning. First, we detect the precursors by ‘Contribution map’. It is a map that produces new output while eliminating the influence of each variable at each point on a trained deep learning model, representing differences using Root-Mean-Square-Difference (RMSD) from the original output. This allows us to detect precursors by interpreting that the greater the difference, the greater the contribution of the variable. The second is a ‘Sensitivity test 0’ that confirms the practical dynamical role of the precursor by replacing index as zero. Third, a ‘Sensitivity test 0.5’ investigates the nonlinearity of response by adding and subtracting 0.5 standard deviation (STD) to original input data and predicts new output to examine the differences between them. An El Nino-Southern Oscillation (ENSO) example allowed us to interpret previously known mechanisms. Therefore, we verify the reliability of our method. Furthermore, by understanding dynamics through deep learning, rather than simply examining the relationship between input and output as a scatter plot, the practical role of each index was revealed.

Presented by

Na-Yeon Shin

Institution

Pohang university of Science and Technology (POSTECH), Division of Environmental Science and Engineering

Keywords

Air-sea interaction, ENSO, climate dynamics, deep learning

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Available Feb 25 22-23h UTC

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Influence of the Indian Ocean warming trend on ENSO

Shreya Dhame, Andréa Taschetto, Agus Santoso, Giovanni Liguori, Katrin Meissner

Abstract

The tropical Indian Ocean has warmed by 1 degree Celsius since the mid-twentieth century. This warming is likely to continue as greenhouse gas emissions keep rising. Here, we discuss how the warming trend could influence the El Niño Southern Oscillation (ENSO) via interaction with the Pacific mean state. The warming trend leads to the strengthening of easterlies in the western equatorial Pacific, subsequent downwelling and an increase in the subsurface temperature gradient in the region and across the equatorial Pacific. In the eastern equatorial Pacific, the response of upwelling ocean currents to surface wind stress decreases, resulting in a weakening of ENSO amplitude. Thus, the Indian Ocean warming trend is found to modulate tropical Pacific mean state and variability, with implications for ENSO predictability under a warming climate.

Presented by

Shreya Dhame

Institution

University of New South Wales

Keywords

Indian Ocean, ENSO, Walker Circulation, Long-term warming, Mean state changes

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Available Thursday February 25th, Poster Session 4

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Pattern recognition methods to separate forced and unforced components of SST pattern changes

Robert Jnglin Wills, David Battisti, Kyle Armour, Tapio Schneider, Clara Deser

Abstract

Ensembles of climate model simulations are commonly used to separate externally forced climate change from internal variability. However, much of the information gained from running large ensembles is lost in traditional methods of data reduction such as linear trend analysis or large-scale spatial averaging. Here, we demonstrate how a pattern recognition method (signal-to-noise-maximizing pattern filtering) extracts patterns of externally forced climate change from large ensembles and identifies the forced climate response with up to 10 times fewer ensemble members than simple ensemble averaging. It is particularly effective at filtering out spatially coherent modes of internal variability (e.g., El Niño, North Atlantic Oscillation), which would otherwise alias into estimates of regional responses to forcing. This method is used to identify forced climate responses within the 40-member Community Earth System Model (CESM) large ensemble, including an El Niño–like response to volcanic eruptions and multi-decadal forced trends in Atlantic sea-surface temperatures (SSTs). The ensemble-based estimate of the forced response is used to test statistical methods for isolating the forced response from a single realization (i.e., individual ensemble members). Low-frequency pattern filtering is found to skillfully identify the forced response within individual ensemble members and is applied to the HadCRUT4 reconstruction of observed temperatures, whereby it identifies potential forced influences on SSTs in the tropical Pacific and tropical Atlantic, with implications for the interpretation of trans-basin interactions.

Presented by

Robert Jnglin Wills

Institution

University of Washington

Other Affiliations

Caltech, NCAR

Keywords

SST pattern, forced climate response, decadal variability, large ensembles

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Available Feb. 25th, 22-23:00 UTC

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Predictability of the super IOD event in 2019 and its link with El Niño Modoki

Takeshi Doi1, Swadhin K. Behera1, and Toshio Yamagata1,2

Abstract

A positive Indian Ocean Dipole (IOD) in 2019 that reached the level of the strongest events occurred in 1994 and 1997 and caused disasters in countries around the Indian Ocean. Using a quasi real‐time ensemble seasonal prediction system based on the Scale Interaction Experiment‐Frontier climate model, its occurrence was predicted a few seasons ahead and the possible impacts were warned by overcoming the so‐called winter predictability barrier. The successful prediction of such a super event at long lead time may contribute to reducing the risks of socioeconomic losses by introducing suitable measures for adaptation. Here, we have investigated possible sources of the successful prediction by analyzing covariability of intermember anomalies defined as deviations from the mean in the ensemble reforecasts. Interestingly, it is found that the potential predictability of the 2019 super positive event is linked with the preexisting El Niño Modoki in the tropical Pacific.

Presented by

Takeshi Doi

Institution

1 Application Laboratory (APL)/Research Institute for Value-Added-Information Generation (VAiG)/Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan 2Institute of Climate and Application Research (ICAR)

Other Affiliations

2 Nanjing University of Information Science and Technology (NUIST), China

Keywords

Indian Ocean Dipole, El Nino Modoki, 2019 super event, seasonal prediction

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Available February 25 at 22h-23h UTC.

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Sub-seasonal sea surface temperature and salinity reconstructions from Northwest Australian corals recording Indonesian Throughflow and Indo-Pacific warm pool dynamics

H. Krawczyk, J. Zinke, J. Lough, N. Cantin, D. Garbe-Schönberg, B. Hambach, P. Wilson

Abstract

The isolated coral reefs of the Northwest Australian shelf are situated in a key region for Indo-Pacific climate connectivity at the edge of the Indo-Pacific warm pool extension into the eastern Indian Ocean. Ocean heatwaves related to El Niño Southern Oscillation have caused severe mass coral bleaching along the NW Australian shelf in recent years. Better understanding and possible predictability of these events, through model-based climate change process studies, heavily depend on reliable climate records. Massive stony corals provide a useful archive of past environmental variability and thus can compensate for the scarcity of long instrumental climate data for the tropical oceans. However, replication studies of the geochemical proxies from several coral cores are necessary to validate the relationship between each proxy and environmental parameter. In this study, we examined monthly variations of Sr/Ca and δ18O of two cores from Porites sp. corals at Browse Island, NW Australia. We assessed the reliability of the coral-based climate records through cross-validation of the geochemical data from the two colonies, as well as through calibration/comparison with instrumental sea surface temperature (SST) records over several decades. Further, paired Sr/Ca and δ18O analyses enabled the reconstruction of the oxygen isotopic composition of the seawater (δ18Osw) and thus provided information about changes in the hydrological balance, mainly driven by evaporation and precipitation and potentially ocean advection from the Indonesian Throughflow. Our results show that reliable climate records can be generated from the Browse Island coral cores, indicating the expansion of the Indo-Pacific warm pool into the Indian Ocean, as well as teleconnections with Pacific Ocean SST anomalies. Such a replication study is of immense importance prior to generating longer proxy records which significantly extend the short instrumental record, leading to a better understanding of the climatic and oceanographic processes.

Presented by

Hedwig Krawczyk

Institution

University of Leicester, School of Geography, Geology and the Environment

Keywords

coral, proxy, SST, SSS, trace elements, stable isotopes, ITF, ENSO

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Available 25.02.2021 22:00-23:00 UTC

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Tropical atmospheric response of Atlantic Niños to changes in the background state

Lea Svendsen, Belén Rodríguez de Fonseca, Elsa Mohino, Lander Crespo, Teresa Losada

Abstract

Warm (cold) Atlantic Niño events during boreal summer can induce La Niña (El Niño)-like events in the Pacific in the following boreal winter. This connection between Atlantic Niños and El Niño-Southern Oscillation (ENSO) events strengthened after the 1970s. We hypothesize that the change in the 1970s was partly due to changes is the ocean background state. To investigate the role of the background state in the Atlantic-Pacific connection, we have analyzed 4 ensemble experiments with three different atmospheric general circulation models (CAM5, SPEEDY and UCLA). In the first two experiments, mean SSTs for the period 1950-1960 and 1965-1975, respectively, are prescribed globally. The first (second) period coincides (In the Atlantic) with a positive (negative) Atlantic Multidecadal Variability (AMV) phase. In addition, we perform two experiments with an Atlantic Niño SST pattern added to the mean SST patterns. We find that during the cold AMV phase, the Atlantic Niño is associated with a westward shift of the Walker circulation compared to during a warm AMV phase. The contribution of the background of the Pacific is also analyzed. There is enhanced low-level convergence over the Maritime Continent, consistent with easterly wind bursts in the western Pacific, which increasing the chance off triggering a La Niña-like event in the Pacific. In addition, the intermember atmospheric spread in climatological runs is significantly higher in the last period that in the former one, suggesting that the increase in tropical atmospheric variability in negative AMV favours the interbasin teleconnection . These results suggest that model simulations of teleconnections can be hampered by systematic model biases, and that ENSO-predictions could be improved in certain periods( modulated by AMV) by taking into account tropical Atlantic variability.

Presented by

MARIA BELEN RODRIGUEZ DE FONSECA

Institution

University of Bergen

Other Affiliations

Universidad Complutense de Madrid

Keywords

Sensitivity experiments, AGCMs, Atlantic Niño impact on Pacific atmospheric variability

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Available February 25 15:00 16:00 pm

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Tropical climate impacts of an Atlantic Meridional Overturning Circulation collapse

Bryam Orihuela-Pinto, Andréa S. Taschetto, Matthew H. England and Agus Santoso

Abstract

Past climatic states have been characterised by a collapsed Atlantic Meridional Overturning Circulation (AMOC), and there is evidence of an AMOC slowdown in today’s climate. Future climate projections suggest further weakening of the AMOC under global warming, which could have significant ramifications for Atlantic heat transport, Arctic sea-ice coverage and regional climate. However, it remains unclear how an AMOC shutdown might impact other regions of the globe. Here we use a global climate model to show how an AMOC collapse can modify the Pacific trade winds and Walker circulation by virtue of the altered heat transport and have consequences for the tropical Pacific mean state and variability. Further global teleconnections are also found across hemispheres and between ocean basins. Given that contemporary climate models neglect meltwater input from Greenland, these findings have important implications for the global climate response to ongoing greenhouse gas increases.

Presented by

Bryam Orihuela-Pinto

Institution

Climate Change Research Centre, University of New South Wales, NSW, Australia

Keywords

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Available February 25 at 22h-23h UTC.

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Two Tropical Routes for the Remote Influence of the Northern Tropical Atlantic on the Indo−western Pacific Summer Climate

Yuhei Takaya, Naoaki Saito, Ichiro Ishikawa, Shuhei Maeda

Abstract

The Asian summer monsoon interacts with the tropical oceans through various processes. Influence of the Indian Ocean on the Asian summer monsoon has been well recognized, and more recently the delayed influence of the El Niño–Southern Oscillation (ENSO), the concept of the Indo-western Pacific Ocean Capacitor (IPOC) mode, has been put forward. While ENSO also modulates the interannual variability of the northern tropical Atlantic (NTA), its influence on the Asian monsoon in the following summer has been less studied.

This study investigates the influence of sea surface temperature (SST) in NTA on the Western North Pacific summer monsoon or IPOC mode by analyzing record-high NTA SSTs summer in 2010. In that time, a decaying El Niño and developing La Niña were accompanied by widespread anomalous climate conditions in the Indo-western Pacific. These conditions are typical of the IPOC mode, which featured the basin-wide warming of the Indian Ocean. Meanwhile, the record-high NTA SSTs was resulted from the influence of the El Niño, the negative phase of the North Atlantic Oscillation as well as the interdecadal-and-longer NTA SST variability.

We conducted a set of sensitivity experiments using a coupled atmosphere−ocean model.　The results indicate that the high NTA SSTs had a considerable influence on the Western North Pacific summer monsoon via two tropical routes: an eastbound route that involved a reinforcement of the atmospheric equatorial Kelvin wave and a westbound route that involved altering the Walker circulation over the Atlantic−Pacific region. The altered Walker circulation facilitated the transition to La Niña, amplifying the impact on the WNP monsoon. Further evaluation reveals that both the interannual and interdecadal-and-longer variability of the NTA SST contributed to the anomalous Indo−western Pacific summer. The results highlight the interannual to multidecadal predictability of the Indo−western Pacific summer climate that originates in the NTA.

Presented by

Yuhei Takaya <yuhei.takaya@mri-jma.go.jp>

Institution

Meteorological Research Institute, Japan Meteorological Agency

Keywords

Asian summer monsoon, Tropical Atlantic, ENSO

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Understanding the SST trends in response to CO2 forcing under inter-basin interactions using idealized model experiments

Sang-Wook Yeh, Yong-Cheol Jeong and Young-Min Yang

Abstract

An upward trend of sea surface temperature (SST) in the global oceans is dominant, which is mostly due to the increase of CO2 concentrations. However, the SST does not respond linearly to the anthropogenic forcings. For example, the global mean SST did not rise significantly around the early 2000s in spite of a gradual increase of CO2 concentration. In addition, the SST warming trend in response to CO2 forcings differs in oceans including the Pacific, Indian and Atlantic basins. This may indicate that the inter-basin interactions play a role to modify the SST warming properties in response to CO2 forcing. To understand these processes, we conduct idealized experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESMv3). We find that there is a specific SST warming trend in response to CO2 forcing based on a single ocean pacemaker experiment in which a free coupling allows to a single ocean basin (i.e., Pacific, Indian and Atlantic ocean, respectively) only with a CO2 forcing. By comparing the observed SST trends with model experiments, we conclude that the inter-basin interactions should be considered to understand a current SST trend in ocean basins.

Presented by

Sang-Wook Yeh

Institution

Hanyang University/South Korea, NUIST/China

Keywords

SST trend, CO2 forcing, Idealized experiments, inter-basin interactions

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Available February 25 at 22h-23h UTC

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Understanding tropical interbasin interaction using linear inverse modelling

Shoichiro Kido, Ingo Richter, Tomoki Tozuka, and Ping Chang

Abstract

Many observational and modelling studies have recently underlined the importance of tropical interbasin coupling in understanding climate variability and predictability. The coupling among tropical basins can be separated into three components; the interaction between Pacific and Indian Oceans (the PO-IO interaction), that between Pacific and Atlantic Oceans (the PO-AO interaction), and that between the Atlantic and Indian Oceans (the AO-IO interaction). Though many previous studies have discussed the significance of individual components, the relative importance of these coupling components has not been carefully evaluated and fully understood. To address this issue, we have constructed a linear inverse model (LIM) based on observed sea surface temperature (SST) anomalies in the tropical Pacific, Atlantic, and Indian Oceans, and performed a series of prediction experiments using this LIM. We found that our LIM has a good skill in forecasting tropical SST variability at lead times of up to 18 months, including those associated with the El Niño and Southern Oscillation (ENSO). To assess the impact of interbasin interaction, we have removed individual coupling component by modifying off-diagonal elements of the linear operator. Using this “decoupled” operator, we have conducted several prediction experiments. We find that the decoupling leads to a substantial decrease in prediction skill of ENSO and related SST variability, especially at longer lead times. Partial decoupling experiments that nullify specific coupling components suggest that the PO-IO interaction has the largest impact on the prediction skill of ENSO-related variability, whereas the PO-AO interaction also has a nonnegligible contribution. On the other hand, the impacts of the AO-IO interaction seem to be smaller than those of the other two coupling components. Results from the LIM simulations with white noise forcing, as well as an analysis of optimum initial conditions will be also discussed. These are aimed to examine the underlying statistical relations and physical processes.

Presented by

Shoichiro Kido

Institution

Japan Agency for Marine-Earth Science and Technology, Application Lab

Keywords

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