Whole Heliosphere and Planetary Interactions (WHPI) Workshop

The solar wind helium abundance (AHe) carries two distinct signatures of the solar cycle. Alterman & Kasper (2019) show that, over long time periods, AHe carries a vsw-dependent phase delay in its response to changes in sunspot number (SSN). In contrast, Alterman et al. (2021) show that AHe rapidly departs and then returns to its solar cycle scale trends approximately 250-days prior to solar minima. Combined, these two results suggest that the vsw-dependent phase delay indicates a change in solar wind source regions and the shutoffs are indicative of global changes in the Sun’s magnetic topology prior to solar wind release, nominally below the chromosphere and transition region. We present these two findings and demonstrate that they enable AHe to serve as a predictor of solar cycle onset.

B.L. Alterman

Southwest Research Institute, BWX Technology, UMD-BC, NCAR

The Sun at solar minimum mostly exhibits low-latitude coronal holes, which are the basis of high-speed streams (HSS) of solar wind. These coronal holes are in preferred longitudes, and exhibit prograde motion, since they can be clustered around the equator which rotates faster than the poles. The coronal holes are disrupted by coronal mass ejections (CMEs), and reform after the CMEs at their preferred longitudes. For all but solar cycle (SC) 21-22, the preferred longitude start for coronal holes of the polarity of the northern hemisphere (NH), is ~270° longitude. The long-lived coronal holes can also restart at their preferred longitude after drifting ~90° prograde (eastward). For Even-Odd solar cycles, the NH polarity coronal holes can be the sole source of HSS at Earth. However, in Odd-Even solar cycles, there is usually an earlier string of long-lived coronal holes with southern hemisphere (SH) polarity that is ~90° west of the NH coronal holes. SC 23-24 is distinguished from the 4 previous solar minimum cycles by 2 or 3 sets of SH low latitude coronal holes, but only one set of NH polarity coronal holes. The coronal hole areas were also larger than in previous cycles.

Barbara Emery <barbara.emerygeiger@gmail.com>

HAO/NCAR

The solar wind and the interplanetary magnetic field perturb significantly the Earth magnetosphere. The aim of the study is to analyze the response of the Earth magnetosphere for various space weather conditions and model the effect of interplanetary coronal mass ejections. The magnetopause stand off distance, open-closed field lines boundary and plasma flows towards the planet surface are investigated. We use the MHD code PLUTO in spherical coordinates to perform a parametric study regarding the dynamic pressure and temperature of the solar wind as well as the interplanetary magnetic field intensity and orientation. The range of the parameters analyzed extends from regular to extreme space weather conditions consistent with coronal mass ejections at the Earth orbit. The direct precipitation of the solar wind on the Earth day side at equatorial latitudes is extremely unlikely even during super coronal mass ejections. For example, the SW precipitation towards the Earth surface for a IMF purely oriented in the Southward direction requires a IMF intensity around 1000 nT and the SW dynamic pressure above 350 nPa, space weather conditions well above super-ICMEs. The analysis is extended to previous stages of the solar evolution considering the rotation tracks from Carolan (2019). The simulations performed indicate an efficient shielding of the Earth surface 1100 Myr after the Sun enters in the main sequence. On the other hand, for early evolution phases along the Sun main sequence once the Sun rotation rate was at least 5 times faster (< 440 Myr), the Earth surface was directly exposed to the solar wind during coronal mass ejections (assuming today´s Earth magnetic field). Regarding the satellites orbiting the Earth, Southward and Ecliptic IMF orientations are particularly adverse for Geosynchronous satellites, partially exposed to the SW if the SW dynamic pressure is 8-14 nPa and the IMF intensity 10 nT. On the other hand, Medium orbit satellites at 20000 km are directly exposed to the SW during Common ICME if the IMF orientation is Southward and during Strong ICME if the IMF orientation is Earth-Sun or Ecliptic. The same way, Medium orbit satellites at 10000 km are directly exposed to the SW if a Super ICME with Southward IMF orientation impacts the Earth.

Jacobo Varela Rodriguez

Universidad Carlos III de Madrid, Plasma Physics group

During severe space weather conditions, there are several phenomena that directly or indirectly affect us, one of them is the Geomagnetic storm. The storm profile explicitly shows three phases i.e. initial, main, and recovery phases. Most of the extreme storms have distinguishable fast and slow recovery phases. Literature suggests that the Co-rotating Interaction Region (CIR) generated storms are weaker but have quite a longer recovery phase than Interplanetary Coronal Mass Ejection (ICME) generated stronger storm recovery phase. In the investigation of specific storm events, we noticed that ICME induced storm recovery phase is quite longer than usual. We indicated that Alfvenic fluctuations could be a possible reason behind this extended recovery phase. Further, we have investigated the fast and slow recovery of extreme storms that occurred in the last three decades. We used exponential, hyperbolic, and linear decay functions to fit the fast and slow recovery of the storms. We observed that exponential and hyperbolic functions are well explained only for fast recovery while slow recovery is well explained by a linear function.

Komal Choraghe

University of Mumbai

The ISWAT clusters H1+2 have focus on interplanetary space and its characteristics. Solar wind structures stemming from the interrelation between large scale open and closed coronal magnetic fields generate periodically recurring regions of compressed plasma and magnetic field followed by high-speed streams. Short-term reconfiguration of the lower coronal magnetic field generates flare emission and provides energy to accelerate enormous amounts of magnetized plasma and particles into interplanetary space. The dynamic interplay between these phenomena changes interplanetary space on various temporal and spatial scales and has effects on the propagation behavior of individual events. Modelling efforts showed that the available observational input is affected by rather large uncertainties, making reliable forecasts difficult. Moreover, the complexity of interplanetary space certainly increases with enhanced solar activity that models cannot cover. Only by joining forces we gain more knowledge about the relation between the different phenomena, underlying physical processes to improve models and to provide better Space Weather forecasting.

Manuela Temmer

Institute of Physics, University of Graz, Austria

Terrestrial LF (Low Frequency, 30-300 kHz) radio sources group different kind of emissions, including time signals, teleswitches, radiolocation beacons (LORAN system), weather services and broadcasting. The first two purposes occupy radio frequencies closer to the Very Low Frequency (VLF) part of the electromagnetic spectrum, which results in lower efficiencies of the emissions despite relatively large transmitter powers. Other emissions, mainly the broadcasting – located in the opposite part of the LF spectrum, employ efficient antenna systems (quarter-wave linear antenna systems) with even higher radiated powers (reaching few megawatts per station) – this makes them well readable on large areas of continental- and worldwide scale. As for the space environment, since 1960s the electromagnetic emissions’ research concentrated on the natural emissions up to 300 kHz (Auroral Kilometric Radiation), which only recently was extended to the detection of human-made emissions coming from the surface of the planet (LORAN’s 100 kHz, VLF submarine communication signals etc.). The analysis of these signals gives information about the propagation of LF electromagnetic waves in the Earth’s magnetosphere, with possible scenarios of its escape towards the interplanetary medium. Numerous space missions have recorded human-made LF signals in the near-Earth environment (example: INTERBALL/Aurora), showing (many years after the actual data registration took place) that the broadcasting part of the LF spectrum (national radio stations sending acoustic signals, time- and frequency standards and teleswitches) is equally well present in the magnetospheric environment of the planet. Due to higher radiated powers of these signals, aided with high antenna efficiencies, these signals present a high advantage in providing data on the behaviour of the planet’s magnetosphere, as well as show a potential way of easy transmission of analogue and digital signals and standards to be received and used onboard orbiting spacecraft. Due to high powers of these emissions, there also exists a high probability of their penetration of the interplanetary environment, if properly calibrated receiving units are allocated onboard interplanetary/interstellar spacecraft. To investigate this phenomena, a series of frequencies is proposed, possible to register with only slightly altered conventional plasma wave detectors (frequency step adjusted / separate indicated frequencies added).

Tomasz Miś

Warsaw University of Technology, Institute of Radioelectronics and Multimedia Technology

We present first results of observations with a new array of Siberian Radio Heliograph consisting of 129 3-meter antennas and operating in 3-6 GHz range. It obtains full-disk images of the Sun every second in 6 frequency channels and both circular polarizations. The combination of sensitivity, spatial and temporal resolution allows us to obtain unprecedented amount of information about the quiet Sun and all kinds of solar activity in microwaves.

Mariia Globa <globa@iszf.irk.ru>

Institute of Solar-Terrestrial Physics, Irkutsk, Russia

Cycle changes in solar magnetic fields from minimum to maximum with a period of about 11 years are manifested in all phenomena of solar activity and determine the state of the interplanetary magnetic field and the parameters of the solar wind. On the basis of data from ground-based and space observatories, a study of the influence of variations in solar polar magnetic fields on the parameters of the solar wind during the minima of solar activity of cycles 21-24 has been carried out. The dependencies of the solar wind parameters on the strength of the solar polar magnetic fields are considered separately for each cycle. The influence of the observed general decrease in the polar magnetic field of the Sun in cycles 21-24 on the changes in the parameters of the solar wind and their interdependencies are estimated. It is shown that the dependencies for different parameters have a different character and differ from cycle to cycle. Whereas at the maxima of solar activity the interplanetary magnetic field and all processes in the interplanetary space are determined by the sectorial structure of the solar magnetic field, the zonal structures of the solar magnetic field dominate at the minima of solar activity. The results showed that the solar wind parameters demonstrate a general decrease in the minimum values from cycle to cycle with the dominance of zonal structures. This is a reflection of the overall decrease in the solar polar magnetic field observed over last cycles.

Irina Bilenko

Sternberg Astronomical Institute

Solar minimum is not a single point in time but rather an extended period of low solar activity when the old and new cycle coexist on the Sun. I used magnetic field and sunspot observations from HMI to study the latitudinal distribution of magnetic flux on the Sun and the transition from cycle 24 to 25 in the 2017-2021 time period. Current spot areas data are not accurate enough to study the evolution of small spot groups during times of low solar activity, so I developed a semi-automatic code to derive sunspot area from the high spatial resolution HMI pseudo-continuum images that allows to accurately detect even small spots and pores commonly seen during solar minimum. The sunspot and magnetic observations from HMI show a long overlap between the two cycles 24 and 25 during the recent minimum when both cycles operated on the Sun, albeit at a very low level, but a quick transition when the new cycle 25 became the dominant cycle.

Guiliana de Toma

NCAR/HAO

We present a statistical study of the X-ray emissions emanating from Jupiter’s disk region using 19 years of observations from the Chandra X-Ray Observatory (CXO). Previous work has suggested that these emissions are consistent with solar X-rays elastically scattered from the planet’s upper atmosphere, and that the Jovian disk emission is governed by solar activity. We showcase a new Pulse Invariant (PI) filtering method which was found to minimise the background and ensures consistency across the nearly-two-decade span of the observations, accounting for Chandra instrument degradation over this period of time. This filtering method ensures that any trends in photon counts have a real physical origin as opposed to an instrumental effect. We compare the CXO results with data from the GOES X-ray Sensor (XRS) in order to quantify the connection between the solar activity cycle and the count rates observed from Jupiter’s disk. The high spatial resolution of the High Resolution Camera Instrument (HRC-I) on board the CXO also allows us to map the disk photons to their specific positions on Jupiter’s surface. As a result, Voronoi tessellation diagrams were constructed to identify any spatial preference of equatorial photons.

Seán McEntee

1 Dublin Institute for Advanced Studies, Ireland, 2 Trinity College Dublin, Ireland, 3 University of Southampton, UK, 4 Harvard & Smithsonian Centre for astrophysics, USA, 5 Mullard Space Science Laboratory, University College London, UK

Neutron monitors (NMs) are ground-based detectors of the secondary particles produced in atmospheric cascades from primary cosmic rays. Using neutron time-delay data from neutron monitors (NMs), we can extract the leader fraction, L, of neutron counts that do not follow a previous neutron count in the same counter tube due to the cosmic ray shower. L is the inverse of the neutron multiplicity and serves as a proxy of the cosmic ray spectral index over the rigidity range of the NM response function. We present a comparative analysis of L from four Antarctic NM stations: South Pole (SP), McMurdo (MC), Jang Bogo (JB) and Mawson (MA). To first order L varies in concert with the count rate C, reflecting unrolling of the Galactic cosmic ray (GCR) spectrum as part of solar modulation during the declining phase of solar cycle 24 and during solar minimum. We use wavelet analysis to study the periodicity of L, the count rate C, and heliospheric parameters to consider their relationship with the 27-day variations. Variation in C was much more variable over 27 days due to high-speed solar wind streams (HSSs) and corotating interaction regions (CIRs), also in strong combination with the higher harmonics, while L usually had a very weak variation. Near the solar minimum of 2019-2020, we observed almost no 27-day variation in C. In contrast, during 2015-2016, near solar maximum, the 27-day variation in L and C was much stronger and fluctuating. Our results indicate weak GeV-range GCR spectral variation due to HSSs and CIRs, relative to the flux variation, in contrast with the strong observed spectral variation due to solar modulation. We acknowledge logistical support from Australia’s Antarctic Program and support from the National Astronomical Research Institute of Thailand and grant RTA6280002 from Thailand Science Research and Innovation.

Pradiphat Muangha

1Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand; 2National Astronomical Research Institute of Thailand (NARIT), Chiang Mai 50180, Thailand; 3Division of Physics, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Pathum Thani 12110, Thailand; 4Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA; 5Department of Physics, University of Wisconsin, River Falls, WI 54022, USA ; 6Department of Earth Science Education, Chonnam National University, Gwangju 61186, South Korea; 7Department of Astronomy, Space Science and Geology, Chungnam National University, Daejeon 34134, South Korea ; 8School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia

During solar minimum activity, the coronal structure is dominated by a tilted streamer belt, associated with the sources of the slowsolar wind. It is known that some UV coronal spectral observations show a quite evident core dimming in heavy ions emission in quiescent streamers. In this poster we show some results about this phenomenon by comparing observed and simulated UV coronal ion spectral line intensities. First, we computed the emissivities and the intensities of HI Lyalpha and OVI spectral lines starting from the physical parameters of a time-dependent 3D three-fluid MHD model of the coronal streamer belt. The model is applied to a tilted dipole (10 degrees) solar minimum magnetic structure. Next, we compared the results obtained from the model in the extended corona (from 1.5 to 4 solar radii) to the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996). We investigate the line-of-sight integration and projection effects in the UV spectroscopic observations, disentangled by the 3D multifluid model. The results demonstrate that the core dimming in heavy ions is produced by the physical processes included in the model (i.e., combination of the effects of heavy ion gravitational settling, and energy exchange of the preferentially heated heavy ions through the interaction with electrons and protons) but it is visible only in some cases where the magnetic structure is simple, such as a (tilted) dipole.

Lucia Abbo <lucia.abbo@inaf.it>

(1) INAF – Astrophysical Observatory of Turin, Pino Torinese (TO), Italy (2) CUA & NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Solar spectral irradiance (SSI) and total solar irradiance (TSI) have been measured from space over the last few minima. We will report on the irradiance levels during the WHPI campaigns, and compare them to the irradiance levels during the WHI (2008) and WSM (1996) periods. Comparing space-based observations over on decadal timescales requires careful understanding of instrument calibration and uncertainties. We will include such details and assess if there is a statistically significant trend in SSI as a function of wavelength for the three minima.

Martin Snow <msnow@sansa.org.za>

South African National Space Agency

In addition to solar modulation according to the ~11-year sunspot cycle and the ~22-year solar magnetic cycle, the time profile of the Galactic cosmic ray (GCR) flux can also exhibit short-term (~2-week) modulation events. These are distinct from Forbush decreases (FDs) in that they are more symmetric in time and evolve over a time scale much longer than the transit of an interplanetary shock and/or coronal mass ejection (CME). Using data from the Princess Sirindhorn Neutron Monitor (PSNM) at the summit of Doi Inthanon, Thailand, with the world’s highest effective vertical geomagnetic cutoff rigidity for a fixed station (16.7 GV), we have examined the solar diurnal anisotropy and find that it exhibited strong peaks during two short-term modulation events in 2012, which were indeed stronger than the diurnal anisotropy variation from sunspot minimum to maximum. We attribute these short-term modulation events to non-local effects of CME shocks. CME shocks (possibly single, multiple, or merged) that propagate beyond Earth inhibit the access of cosmic rays for ~2 weeks. The direction of anisotropy enhancement favors an explanation in terms of cosmic ray diffusion perpendicular to the interplanetary magnetic field, which eventually causes the cosmic ray flux to stop decreasing and gradually recover.

Nutthawara Buatthaisong

Mahidol University

We describe the energy budget of a coronal mass ejection (CME) observed on 1999 May 17 with the SOHO/UVCS instrument. We constrain the physical properties of the CME's core material as a function of height along the corona by using the spectra and photometry taken by the single-slit coronagraph spectrometer at heliocentric distances of 2.6 and 3.1 solar radii. We use plasma diagnostics from intensity ratios, such as the O VI doublet, to determine the velocity, density, and temperature of the core material. We perform non-equilibrium ionization calculations to determine the ionization states and focus primarily on H I, O V, O VI, and C III. Using these observationally constrained physical properties, we deduce the initial conditions of the CME with respect to the various plasma heating parameterizations we investigated. Amongst the four ions we accounted for, we find that the CME core's velocity is about 250 km/s, and its cumulative heating energy is comparable to its kinetic energy.

Maurice Wilson

Center for Astrophysics, Harvard & Smithsonian; University of Michigan, Dept of Climate and Space Sciences and Engineering; Predictive Science Inc.

The modern Heliophysics System Observatory (HSO) allows for comprehensive measurements of the suprathermal ion content associated with a given Corotating Interaction Region (CIR) at different heliographic radial distances. In this study, we compare observations at both Solar Orbiter and ACE to investigate the radial dependence of CIR-associated suprathermal ion intensities and spectra. These radial profiles are compared to observations from Helios and IMP 8 from Van Hollebeke et al. (1978). Additionally, we compare the recent CIR-associated suprathermal ion spectra in the current solar minimum to that observed during the last solar minimum. The Solar Orbiter and ACE observations reveal a radial profile of CIR-associated suprathermal ion intensities that is remarkably consistent with that reported by Van Hollebeke et al. (1978), however, the suprathermal ion intensities are much weaker than those seen in the previous solar cycle. Future observations utilizing the HSO will continue to deepen our understanding of these variations in solar wind populations and their origins.

Robert Allen

Johns Hopkins University Applied Physics Lab

Major disturbances in earth’s magnetosphere generated due to huge amount of energy transfer form solar wind in to space environment around the earth are considered as Geomagnetic storm. Solar wind consists of photon and electron emitted from sun with approximate speed of 400km/sec with temperature of 1 million degree Celsius. The interaction between solar wind and magnetic field of earth increase the plasma level in earth magnetosphere due to transfer of energy, which increases the movement of electric current in the earth outer atmosphere. Also horizontal component of magnetic field shows significant changes at low latitudes during geomantic stroms. In case of classical magnetic storm, horizontal component of magnetic field shows abrupt change in with respect to storm sudden commencement and decrease rapidly with ring current intensity, which is recognized as main phase. During this time direction of interplanetary magnetic field is southward, when it becomes northward ring current becomes to recover and low latitude H-component start rising and attend its quiet time value called recovery phase. Here we have analyzed the IMF, solar wind plasma and Dst index during major geomagnetic storms during solar cycle 24 with statistical methods. The interrelationship between these parameters should be analyzed using scattered plot and cross correlation techniques.

Deepak Kumae Sondhiya

School of Scienes, SAGE University Bhopal, India

In support of the Whole Heliosphere and Planetary Interactions (WHPI) effort and to highlight solar structure near solar minimum we are producing solar synoptic maps featuring coronal hole boundaries for the WHPI extended minimum period (September 2018 – February 2020 or CR’s 2209 – 2227) and two of the Parker Solar Probe times of interest CR2239 (Dec. 2020 – Jan. 2021) and CR2242 (Mar. – Apr. 2021). These maps are made from two positions around the sun using SDO and Stereo EUV data. With SDO 193 and 305 angstroms are used and with Stereo A 195 angstroms. These maps, made in the manner established by Patrick McIntosh and used in the McIntosh Archive of Synoptic maps, enable studies of solar features and their relation to structures in the solar wind and space environment of the earth and other planets. For the Stereo A maps, we will try to correlate fluctuations in solar wind data with specific coronal holes. During the Carrington Rotations that Stereo A is well aligned with Mars we will try to correlate fluctuations in solar wind data at Maven with specific coronal holes. From the SDO-based maps with the Earth's perspective, we will trace solar wind back to its footpoints at coronal holes and their boundaries using the SolarSoft PFSS codes of M. DeRosa and compare it to the CCMC model runs for each Carrington Rotation. This data will be supplemented with OMNI solar wind data showing velocity, amplitude on the AP index, Bz and DST. In addition, 'hairy sun' PFSS models showing open and closed field lines will be included. This data will be organized to show a sort of mosaic of coronal hole and solar wind data. The result will be a comprehensive look at the organization of coronal holes and high speed solar wind streams for each Carrington Rotation during the solar minimum period and the Parker Solar Probe post minimum Carrington Rotations of interest.

Ian Hewins

HAO/NCAR

Solar nanoflares are small eruptive events releasing magnetic energy in the quiet corona. If nanoflares follow the same physics as their larger counterparts, they should emit hard X-rays (HXRs) but with a rather faint intensity. A copious and continuous presence of nanoflares would result in a sustained and persistent emission in HXRs, which in turn would deliver enormous amounts of energy into the solar corona, possibly accounting for its high temperatures. To date, there has not been any direct observation of such sustained and persistent HXRs from the quiescent Sun. However, Hannah et al. in 2010 constrained the quiet Sun HXR emission using almost 12 days of quiescent solar-off-pointing observations by RHESSI. These observations set 2σ upper limits at 3.4x10-2 photons-1 s-1 cm-2 keV-1 and 9.5x10-4 photons-1 s-1 cm-2 keV-1 for the 3-6 keV and 6-12 keV energy ranges, respectively. Observing feeble HXRs is challenging because it demands high sensitivity and dynamic range instruments in the HXR energy band. The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment excels in these two attributes when compared with RHESSI. Particularly, FOXSI completed its third successful flight (FOXSI-3) on September 7th, 2018. During FOXSI-3’s flight, the Sun exhibited a fairly quiet configuration, displaying only one aged non-flaring active region. Using the entire ~6.5 minutes of FOXSI-3 data, we constrained the quiet Sun emission in HXRs. We found 2σ upper limits in the order of ~10-3 photons-1 s-1 cm-2 keV-1 for the 5-10 keV energy range. FOXSI-3's upper limit is consistent with what was reported by Hannah et al., 2010, but FOXSI-3 achieved this result using ~1/2640 less time than RHESSI. A possible future spacecraft using FOXSI's concept would allow enough observation time to constrain the current HXR quiet Sun limits further or perhaps even make direct detections.

Milo Buitrago-Casas

(1)University of California Berkeley, Space Sciences Laboratory (2)University of Minnesota (3)NASA Marshall Space Flight Center (4)NASA Goddard Space Flight Center (5)National Astronomical Observatory of Japan (6)Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (7)University of Tokyo, Bunkyo, Tokyo (8)Georgia Tech Research Institute (9)University of Applied Sciences Northwestern Switzerland. (10) Johns Hopkins University Applied Physics Laboratory. (11) ESA, European Space Research and Technology Centre.

Since late 2014, contemporaneous measurements of thermospheric density have been made at Earth and Mars with near identical sensors. LYRA onboard PROBA2 and EUVM onboard MAVEN are in orbit at Earth and Mars, respectively, and both measure thermospheric density with EUV foil filter photometers by the method of solar occultations. Because solar occultations are constrained to the terminator, local time is inherently controlled for, reducing ambiguity in comparisons of measurements made at Earth and Mars. As such, these two instrument provide a rare opportunity for direct comparisons of thermospheric variability at Earth and Mars as the two the planets are subject to the same solar forcing. In this presentation, we compare thermospheric variability at Earth and Mars from late 2014 through solar minimum. We show that the Mars thermosphere is, on-average, about half as sensitive to EUV forcing as that of Earth. We also compare the response of both planets to EUV forcing from the Big Sunspot of 2014. Finally, we compare the day-to-day variability at solar minimum, presumably dominated by wave forcing from below, and place the magnitude of this variability in the context of that due to solar EUV forcing.

Ed Thiemann

(1) University of Colorado; (2) Royal Observatory of Belgium; (3) University of Michigan; (4) George Mason University

The Karl G. Jansky Very Large Array (VLA) has a long history performing Faraday rotation (FR) studies of the solar corona. FR is the rotation of the polarization position angle when linearly polarized radiation propagates through a magnetized plasma, providing a ground-based method for probing the coronal magnetic field at heliocentric distances within 20 solar radii. Over the last year, we used the VLA to observe coronal FR at 1-2 GHz to provide important contextual information for the Parker Solar Probe (PSP). In order to enhance the scientific results from PSP, it is crucial to supplement these in situ measurements with ground-based radio remote-sensing observations. To support the PSP mission, we made VLA observations on fixed dates corresponding to PSP perihelion events #5, 6, and 7 (June 2020, September 2020, and January 2021, respectively). We observed FR through coronal plasma structures at heliocentric distances within 20 solar radii, coinciding with PSP's trajectory. By combining these VLA FR observations with magnetic field measurements from the FIELDS instrument onboard PSP, we simultaneously probe the coronal magnetic field over distances of 4.6 to 36 solar radii. Using these VLA and PSP data, we have calculated updated power-law models for the coronal magnetic field in 2020 and early 2021, ranging from a single-term interplanetary magnetic field model to a more complex dipole-quadrupole-current sheet model.

Jason E. Kooi

U.S. Naval Research Laboratory

The variation of inner zone proton flux, reaching a maximum following the Solar Cycle 23 and 24 solar minima which occurred in 2008 and 2019, has been compared using POES NOAA-15 proton fluxes at energies >35, >70, and >140 MeV. The delay in the flux minimum in the South Atlantic Anomaly relative to the F10.7 maximum flux was determined as a function of energy and compared with previous studies1, 2. Prior to 2015, proton flux from POES has been used to study long term variability going back to 1980, with the strongest flux maximum occurring for the particularly deep solar minimum in 20081 evident in other measures of solar and solar wind energy input to geospace. A comparison with the 2019 solar minimum when high speed streams connected to coronal holes provided stronger driving to the magnetosphere extends prior studies of the solar cycle dependence of inner zone protons.

Emily Bregou <ebregou@sas.upenn.edu>

High Altitude Observatory, University of Pennsylvania, Dartmouth College, Boston University, University of Colorado, National Centers for Environmental Information

The impact of High-speed Solar Wind Streams, HSSs, and Corotating Interaction Regions, CIRs, during the last two solar minima on the Brazilian low latitude ionosphere is investigated. HSSs are emanated by coronal holes and propagate in the interplanetary medium where they reach preceding low-speed streams creating Corotating Interaction Regions, CIRs. These structures are characterized by high plasma density and strong and highly oscillatory magnetic fields. When they arrive at the Earth’s magnetosphere, southward excursions of IMF_Bz lead to reconnection processes with the geomagnetic field responsible for the occurrence of geomagnetic storms and multiple processes from high to low latitudes. The low-latitude ionosphere in the Brazilian sector is markedly characterized by complex electrodynamics processes, especially owing to the high negative declination angle of the magnetic field, which results in strong plasma density gradients and in the development of large-scale plasma irregularities, or plasma bubbles responsible for ionospheric scintillation processes. Scintillation processes can cause errors and loss of lock of the radio signals, which can severely affect global navigation and positioning systems as well as radio wave communications. Although the low latitude ionospheric variability is well-known, the effects of CIR/HSS-driven storms were not yet extensively investigated. In this way, this work aims to get a better understanding of the impact of CIR/HSS-driven storms on the Brazilian low-latitude ionosphere during solar minimum. For this purpose, we analyzed ionospheric parameters such as Total Electron Content (VTEC) and other ground-based ionospheric parameters. It is observed intensifications and depletions in the ionospheric density, as well as the development or suppression of plasma irregularities in distinct disturbed intervals. A spectral analysis using a wavelet technique was also performed and revealed distinct features between the last two solar minima.

Claudia Nicoli

National Institute for Space Research, INPE ; University of Vale of Paraíba, UNIVAP

The solar cycle directly influences the solar irradiance that impinges upon planetary atmospheres. These variations can affect the rate at which atmospheric species escape from planets. Observations by the Mars Atmosphere and Volatile Evolution (MAVEN) mission and the Hubble Space Telescope (HST) have been used to constrain the properties of the atomic species D and H at Mars. These observations span solar activity extrema and are used to constrain the abundances and escape rates of these water-spawned atoms to investigate their variability with solar cycle. Results show large inter-annual variability in the properties of these species, and that the escape rates of both D and H atoms decrease markedly at times of lower solar activity, mainly due to a decrease in atmospheric temperature. The findings suggest that while reduced solar irradiance conditions may enhance the abundance of H atoms in the upper atmosphere of Mars, this does not increase their escape rates due to cooler atmospheric temperatures resulting from decreased solar EUV flux.

Majd Mayyasi

Center for Space Physics, Boston University

What drives the total solar irradiance (TSI) changes during a deep solar minimum, i.e., during practical absence of detectable sunspot groups and long-lasting active regions? The abundant data sets comprising X-ray, UV and visible measurements show that in June-October 2008 the pronounced (at ~10-sigma level) TSI variability detaches from the patterns seen in EUV. TSI, however, follows the changes in the relative surface area coverage by strong magnetic fields, as well as the variations of the MgII index. The reviewed data are yet to reveal the nature of the elusive TSI driver.

Sergey Marchenko

Science Systems and Applications, Inc., and NASA Goddard Space Flight Center