Many extreme solar events were observed in May 2024 as the sun was approaching the solar maximum of Solar Cycle 25. We report observations of Martian proton aurora caused by extreme space weather that impacted Mars during 17-21 May. Using data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, we observe significant and persistent proton aurora activity at Mars, with peak intensities that exceed ~32 kR and emission enhancements that approach 15 kR. We also observe extremely high solar wind proton densities, velocities, and energy fluxes, as well as significantly elevated upstream magnetic field magnitudes and fluctuations during these orbits. The proton aurora events that were caused by this extreme solar activity in May 2024 represent the highest intensity continuous proton aurora detections that have ever been observed by any Mars asset. These observations advance our understanding of the controlling factors that influence major proton aurora activity at Mars.

The International Space Weather Action Teams (ISWAT) is a grass-roots initiative that emerged as a global force from a small group of original founders in just a few years. ISWAT, hosted by the COSPAR Panel on Space Weather (PSW), serves as a hub for self-organised topical collaborations addressing space weather challenges, from solar origins to impacts on Earth and other planets. ISWAT has an infrastructure of action teams grouped into clusters by spatial domains and physical phenomena, that encompass overarching activities, and facilitate teamwork without borders or barriers. Anyone in the community can create a team, or join an existing team by completing a simple online application form. ISWAT is a professional, high-expertise community that encourages the participation of early-career scientists and provides research, and high-level mentorship, and encourages team co-leadership by researchers at different career stages. The joint activities of ISWAT mutually benefit participants, supplement core independent capabilities and maximise return on international/national/regional agencies’ investments in space weather efforts.ISWAT was a driving force behind the COSPAR PSW-ISWAT Space Weather Roadmap. Many of the science papers for the Roadmap Special Issue 1 (Science and Applications) were led by the ISWAT Action Teams. The review papers for the COSPAR Special Issue 2 (Achievement and Future Goals, this issue) are aligned to mirror the ISWAT cluster structure. This paper narrates the history of ISWAT, describes its structure, core principles, and current status, and presents perspectives on ISWAT post-Roadmap activities while Bisi et al. (2026, this issue) provides the overarching outcomes of this Roadmap endeavor. The special focus of this manuscript is to lay out the plans for addressing Roadmap recommendations and to improve the cross-cluster working. Additional actions include establishing a new user-focused space weather training network, and exploring opportunities for collaborative shared environments and community modeling. First results are expected by the next ISWAT Working Meeting in spring 2027. ISWAT is aiming to provide a seedbed for a new generation of leaders and to serve as a resource for the International Space Weather Coordination Forum.

Magnetic fields around Mars shape the pathways of energy input into, and ion escape from, the Martian atmosphere, thereby potentially affecting the atmospheric evolution of Mars. The Martian magnetic field environment is primarily determined by the global electric current system resulting from the solar wind interaction with the upper atmosphere and crustal magnetic fields of Mars. Recently, it has been recognized that neutral wind-driven ionospheric dynamo currents generate magnetic field perturbations observable in orbits and on the surface of Mars. However, the entire system of near-Mars currents is not fully understood. Here we present a newly identified current system in the Martian magnetosphere directly coupled to the wind-driven ionospheric currents, based on the spherical harmonic analysis of magnetic field data obtained by the Mars Atmosphere and Volatile Evolution spacecraft. This magnetospheric current system can be explained by diamagnetic currents associated with magnetic fields generated by the wind-driven ionospheric dynamo currents. Our results demonstrate a close coupling between the neutral atmospheric dynamics and the high-altitude magnetospheric current system at Mars mediated by wind-driven ionospheric dynamo currents. This reveals a previously unrecognized role of the neutral atmosphere in controlling magnetic field environments of unmagnetized planets.

We evaluate for the first time the large-scale influence of the upstream interplanetary magnetic field (IMF) magnitude and orientation on Martian proton aurora. We specifically look at IMF magnitude and orientations to consider how these factors influence the brightness and likelihood of occurrence for proton aurora activity. Ten years of proton auroral observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft (Jakosky et al., 2015) are utilized in this study. We identify a moderate correlation between proton aurora activity and IMF magnitude that varies seasonally, with highest correlations around Mars southern summer solstice when proton aurora activity reaches an annual high. We also identify preferentially increased proton aurora emission enhancements at IMF cone and clock angles consistent with the shape of the Parker spiral at Mars’s heliocentric distance. An increased proton aurora occurrence rate is observed for near- and quasi-radial IMF orientations, however, this correlation is only observed during seasons other than around southern summer solstice, when the hydrogen corona and bow shock are annually decreased. Lastly, proton aurora are observed to exhibit preferentially higher occurrence rates under strong ±Bz orientations, consistent with the findings of recent studies (e.g., Bowers et al., 2023) which identified conditions of increased likelihood for dayside magnetic reconnection at Mars (i.e., between the IMF and Martian crustal fields) for similar altitudes and geographic locations. Thus, our results suggest that dayside magnetic reconnection may influence Martian proton aurora occurrence. These findings enhance our understanding of the interconnected relationship between proton aurora and the Mars magnetic field environment, as well as the upstream IMF’s role as an important driver of Martian proton aurora activity.

Recent observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) spacecraft have suggested that pressure pulses originating from upstream proton cyclotron waves (PCWs) can "ring" the Martian magnetopause at the same frequency and drive magnetosonic waves in the upper ionosphere of Mars, thereby transporting energy from the solar wind into the ionosphere. However, the limitation of single-spacecraft measurements prevents simultaneous observations of the driver and response of this "ringing" process of the Martian magnetosphere. Here we utilize two-point measurements from MAVEN and MEX to characterize the ringing probability at which upstream PCWs drive compressional fluctuations in the ionospheric magnetic field. We develop an algorithm to identify PCW-driven magnetosonic waves in the upper ionosphere of Mars from the two-point magnetic field data. The derived ringing probability is higher on the dayside, outside strong crustal magnetic fields, and under high solar wind density conditions. We also show that the median power of dayside ionospheric magnetic field fluctuations is enhanced by a factor of similar to 2 at corresponding frequencies in the presence of upstream PCWs compared to the median power in the absence of upstream PCWs. These results demonstrate the prevalence of energy deposits into the dayside Martian ionosphere from the solar wind mediated by the PCW-driven ringing of the magnetosphere. Future studies, possibly with new multi-point observations, should address the detailed processes of wave propagation and energy transport through the system and the long-term impact of this chain of processes on the planetary ion heating in the ionosphere and atmospheric loss from Mars.

We compare observations of hydrogen (H) and protons associated with Martian proton aurora activity, co‐evaluating remote sensing and in situ measurements during these events. Following the currently understood relationship between penetrating protons and H energetic neutral atoms (ENAs) in the formation of proton aurora, we observe an expected correlation between the H Lyman‐alpha (Ly‐ α ) emission enhancement (used herein as a proxy for H‐ENAs) and penetrating proton flux. However, we also observe a notable spread in the trend between these two data sets. We find that this spread is contemporaneous with one of two major impacting events: high dust activity or extreme solar activity. Proton aurora events exhibiting a relative excess in penetrating proton flux compared to Ly‐ α enhancement tend to correspond with periods of high dust activity. Conversely, proton aurora events exhibiting a relative deficit of penetrating proton flux compared to Ly‐ α enhancement are qualitatively associated with periods of extreme solar activity. Moreover, we find that the largest proton aurora events occur during concurrent dust storm and solar events, primarily due to the compounding intensified increase in H column density above the bow shock. Finally, we present a simplified empirical estimate for Ly‐ α emission enhancement during proton aurora events based on the observed penetrating proton flux and a knowledge of local dust/solar activity at the time; this estimate provides a straightforward method for predicting auroral activity when direct observations are not possible or available. The results of this study advance our understanding of the interconnected relationship between H and protons during Martian proton aurora activity.

Upstream of quasi-parallel bow shocks, reflected ions generate ion–ion instabilities. The resulting magnetic fluctuations can advect through the shock and interact with planetary magnetospheres. The amplitude of magnetic fluctuations depends on the strength of the shock, quantified by the Alfvén Mach number ( M _A ), which is the ratio of solar wind velocity to the local Alfvén velocity. With increasing heliocentric distance, the solar wind M _A generally increases, such that Mercury typically experiences a lower M _A ∼ 5 compared to Earth ( M _A ∼ 8), and Mars a slightly higher M _A ∼ 9. Farther out in the solar system, Saturn has even higher M _A (∼10). However, the solar wind flow is highly irregular, and on top of solar cycle variations these values for average M _A at each planet do not capture extreme events. Statistical analysis of OMNIWeb observations from 2015 to 2023 shows that sustained (30 minutes or more) high M _A (30–100) occurs at Earth about once a month. Using a selection of events in the ion foreshock regions of Mercury, Earth, Mars, and Saturn, a linear scaling is calculated for the maximum magnetic fluctuation amplitude as a function of M _A . The resulting slope is ∼0.2. Based on the dominant fluctuation frequency for the largest-amplitude events at each planet, it is found that Mars exists in a special regime where the wave period of the magnetic fluctuations can be similar to or longer than the magnetospheric convection timescale, making Mars more susceptible to space weather effects associated with foreshock fluctuations.

Martian diffuse auroras are ultraviolet emissions spread across the nightside of Mars caused by solar energetic particles (SEP), both electrons and protons. The nightside structures of induced and crustal magnetic fields are expected to affect the diffuse auroral emission profiles caused by electrons, which is far from understood. Here we estimate magnetic field effects on emission based on a newly developed Monte Carlo model simulating collisions and electron cyclotron motions. Parameter surveys of the magnetic field intensity and dip angle (angle of magnetic field line from horizontal direction) under uniform magnetic field structure show that the effects of magnetic field dip angle on auroral altitude profiles are greater than those of magnetic field intensity. We then applied our model to the September 2017 diffuse aurora event using MAVEN SEP electron flux observations and neutral atmospheric profile from the Mars Climate Database as inputs. Comparison between horizontal and vertical magnetic field dip angle cases indicates that the horizontal dip angle case results in broader limb-integrated auroral altitude profiles than the vertical case and enhances the auroral intensity at high altitudes (>75 km). The magnetic field structure can be one of the important factors in understanding the Martian diffuse auroras.

The Martian magnetotail is a dynamic region where several processes contribute to plasma acceleration. Here, we analyze years of Mars Atmosphere and Volatile EvolutioN (MAVEN) data to evaluate the role of magnetic tension forces in driving plasma acceleration within current sheets in the tail. Based on magnetic field measurements, we identify 547 current sheet crossings that follow a Harris profile and find that the median observed current sheet density is 110 nA , with a typical sheet width of 100 km. We estimate a median normalized of 0.1, and force of N , capable of accelerating planetary ions within the sheets to 1 keV over 2 . We also analyze plasma energization signatures in nine high‐ case studies and find they can be explained by work done by , although observed ion differential streaming suggests additional forces may be present.

Magnetic reconnection is a fundamental mechanism for the transport of mass and energy in planetary magnetospheres and astrospheres. While the process of reconnection is itself ubiquitous across a multitude of systems, the techniques used for its analysis can vary across scientific disciplines. Here we frame the latest understanding of reconnection theory by missions such as NASA’s Magnetospheric Multiscale (MMS) mission for use throughout the solar system and beyond. We discuss how reconnection can couple magnetized obstacles to both sub- and super-magnetosonic upstream flows. In addition, we address the need to model sheath plasmas and field-line draping around an obstacle to accurately parameterize the possibility for reconnection to occur. We conclude with a discussion of how reconnection energy conversion rates scale throughout the solar system. The results presented are not only applicable to within our solar system but also to astrospheres and exoplanets, such as the first recently detected exoplanet magnetosphere of HAT-11-1b.

Abstract We report on observations made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, in the shocked solar wind‐ionosphere interface of Mars. We observe a strong asymmetry in plasma flow governed by the direction of the motional electric field. In the hemisphere, in which the motional electric field ∼−V × B is pointed outward the planet the solar wind flow is decelerated by the j × B force related to the magnetic field compression in the barrier. In contrast, in the opposite hemisphere, the solar wind flow is accelerated. The gain in velocity is about 100–200 km/s. The dynamics of ionospheric ions are also very different on both sides. Such an asymmetry implies very different patterns of the electric current closure and the electromagnetic forces in both hemispheres.

Solar wind turbulence is a dynamical phenomenon that evolves with heliocentric distance. Orbiting Mars since 2014 September, Mars Atmosphere and Volatile EvolutioN offers a unique opportunity to explore some of its main properties beyond ∼1.38 au. Here, we analyze solar wind turbulence upstream of Mars' bow shock, utilizing more than 5 years of magnetic field and plasma measurements. This analysis is based on two complementary methodologies: (1) the computation of magnetohydrodynamic (MHD) invariants characterizing incompressible fluctuations; (2) the estimation of the incompressible energy cascade rate at MHD scales (i.e., 〈 ε ^T 〉 _MHD ). Our results show the solar wind incompressible fluctuations are primarily in a magnetically dominated regime, with the component traveling away from the Sun having a higher median pseudoenergy. Moreover, turbulent fluctuations have a total energy per mass of up to ∼ 300 km ^2 s ^−2 , a range smaller than reported at 1 au. For these conditions, we determine the probability distribution function of 〈 ε ^T 〉 _MHD ranges mainly between ∼ −1 × 10 ^−16 and ∼1 × 10 ^−16 J m ^−3 s ^−1 , with a median equal to −1.8 × 10 ^−18 J m ^−3 s ^−1 , suggesting back transfer of energy. Our results also suggest that ∣〈 ε ^T 〉 _MHD ∣ is correlated with the total energy per mass of fluctuations and that the median of 〈 ε ^T 〉 _MHD does not vary significantly with the cross-helicity. We find, however, that the medians of the inward and outward pseudoenergy cascade rates vary with the solar wind cross-helicity. Finally, we discuss these results and their implications for future studies that can provide further insight into the factors affecting the solar wind energy transfer rate.

It has been long observed at Mars that electron fluxes are enhanced during the tail current sheet crossings, of which the cause is not well understood. We use a novel approach to reveal one of the electron energization mechanisms with observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. We find the field-aligned potential, derived from comparing electron distribution functions, to be approximately linearly correlated with the logarithmic values of the local total ion density. This is the expected behavior of an ambipolar electrostatic potential. The large amplitude of potential (tens to hundreds of V) is a result of both a significant density gradient (1 order of magnitude) and the high electron temperature (tens of eV) in the tail. Such a mechanism is not limited to ion density enhancements at current sheet crossings but can be present anywhere that large ion density gradients and hot electrons are present.

The dominant form of mass and energy transport between the Sun and the Ice Giant magnetospheres of Uranus and Neptune remains an open question. Predictions based on theory suggest that a combination of the weaker internal magnetospheric plasma sources and significantly tilted magnetic dipole fields of Uranus and Neptune may enable increased solar wind-magnetospheric coupling. Much of this coupling is dependent on the local solar wind parameters, specifically the Alfvénic Mach number (MA). Despite predictions of transport driven by solar wind coupling, the Voyager 2 flyby of Uranus observed a large MA of ~23 and a loop-like plasmoid in the magnetotail, suggestive of more internal planetary plasma driving. In order to better constrain the possible scenarios of internally-driven vs. externally-driven magnetospheric convection at a given planet, a quantitative assessment of upstream plasma variations is required. The interaction between the solar wind and a planetary magnetosphere is often parameterized in terms of MA, with lower values enabling enhanced rates of magnetopause reconnection and energy exchange between the interplanetary and planetary environments. Here we perform a comprehensive analysis of upstream MA throughout the solar system using data spanning from 0.3 AU to 75 AU, collected by the Helios 1 & 2, Voyager 1 & 2, and Pioneer 10 & 11 spacecraft from 1972-2005. We find that systematic increases in solar wind magnetic pressure during periods of high solar activity lead to lower-than-expected MA upstream of the giant planets. These lower MA values combined with the significant tilt of the magnetic dipole axes at Uranus and Neptune likely result in amplified solar-wind-magnetospheric coupling at solar maximum. The results indicate that magnetospheric dynamics at Uranus and Neptune may be strongly dependent on solar cycle.

Abstract. Flux transfer events (FTEs) are magnetic flux ropes formed by multiple reconnection X-lines on the magnetopause between the planetary magnetic field and the interplanetary magnetic field (IMF). During FTE shower intervals, FTEs appear extremely frequently with typical rates of ~ 10 FTEs per minute. This study shows that FTE showers are observed during half of the dayside magnetopause crossings over the entire MESSENGER mission. The occurrence and physical properties of FTE showers depend on the magnetic shear angle across the magnetopause and the magnetosheath plasma (ratio of the plasma thermal pressure to the magnetic pressure). Modeling of these flux ropes in FTE shower intervals are determined to carry most (i.e., 60% - 85%) of the magnetic flux supplying Mercury’s Dungey cycle. Furthermore, sodium ions (Na+) are substantially enhanced during FTE shower intervals as compared with non-shower intervals. FTE showers lead to much larger precipitation rates on the cusp’s surface and would sputter large numbers of planetary atoms into the exosphere, which then be photon-ionized resulting in the enhancement of Na+. 1. Introduction. Interactions between Mercury’s global intrinsic magnetic field and supersonic solar wind form a miniature magnetosphere. Without a significant neutral atmosphere, Mercury’s magnetosphere is able to prevent most of the planet’s surface from being directly hit by the streaming solar wind most of the times [1]. Magnetic reconnection on the dayside magnetopause generates FTEs, in which the magnetic field lines have one end connected to the solar wind and the other end connected to the planet. Magnetic flux ropes concentrate magnetic flux in the FTEs (FTE-type FRs), which transport magnetic flux from the dayside magnetosphere into the nightside following the convection of FTEs. Solar wind plasma can be transported along the magnetic field lines and precipitate to the surface at the planet’s cusps causing sputtering [2]. MESSENGER observations have shown that FTE showers correspond to a very high occurrence of FTEs (~ 10 FTEs per minute) [1, 3]. In this work, we investigate how the low Alfvénic Mach number (MA = VSW/VA) solar wind near Mercury’s orbit influences the occurrence and physical properties of FTE showers, and how FTE showers contribute to the Dungey cycle and influence sodium ions dynamics in the dayside magnetosphere. 2. FTE Shower at Mercury

On 26-27 December 2022, Mars experienced an extremely low-density solar wind stream, which was encountered first by Earth because of the radial alignment of the two planets (i.e., Mars opposition). During this event, two important properties of the ionospheric and magnetospheric states changed significantly in response to the low solar wind ram pressure, as inferred from the superthermal electron observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. The interface between the ionosphere and magnetosphere expanded to thousands of kilometers, outside of the nominal bow shock locations, coinciding with the expansion of the cold planetary ions. Meanwhile, the ambipolar electrostatic potential arising from the ionospheric electron pressure gradient increased from the nominal similar to -0.7 to similar to -2 V (relative to the lower ionosphere). This enhanced ambipolar potential likely facilitated the observed ionosphere expansion. This study characterizes Mars's magnetospheric and ionospheric response to the disappearing solar wind event in December 2022 During the event, open and closed field lines extend beyond the nominal bow shock location, just as the planetary cold ions The ionospheric ambipolar potential drop is enhanced from the nominal similar to -0.7 to similar to -2 V, likely facilitating the ionosphere expansion

AbstractHeavy cold ions at Mars are gravitationally bound to the planet unless some process provides energy to them. Observations show that cold (<20 eV) and dense (∼>1 cm−3) O+/O2+ ions with bulk velocities equal to energies ∼1 keV can reach deep into the nightside Martian magnetosheath. These ions are co‐located with a change of the sign of the sunward component of the magnetic field. This magnetic field topology implies the persistence of a localized planetary ions escape channel associated with draped magnetic field lines that are convecting tailward. The observed ion populations propagate approximately in the same direction as surrounding magnetosheath flow and are likely to be almost unheated ionospheric ions from low altitudes. The paper discusses planetary ion energization via Hall electric field originated from ions and electron separation associated with magnetic field curvature.

Magnetic flux ropes – helical magnetic structures which are produced due to simultaneous reconnection at multiple X-lines, have been observed at the magnetospheres of most magnetized planets. The size of these flux ropes, also called “plasmoids” if they contain significant plasma pressure, can vary from being a significant fraction of the system size (e.g. tens of Earth radii at the terrestrial magnetotail) to small flux ropes with diameters less than the local ion inertial length. The smallest flux ropes are expected because reconnection in the Earth’s cross-tail current sheet only occurs when it thins to or below the ion-inertial scale and tearing instabilities produce periodic X-lines with spacing of ~2 times the thickness of the current sheet. While much is still to be understood, it is hypothesized on the basis of Particle-in-Cell simulations that the smaller flux ropes soon come together and “coalesce”, via reconnection, into larger flux ropes. The coalescence process continues until the observed distribution of plasmoid diameters is produced. For the giant magnetospheres like Jupiter, which encompass multiple moons that lose mass to the rapidly rotating inner plasma disk, the momentum in the outer layers of the disk is believed to continuously shed mass by the release of plasmoids down the tail plasma sheet. This periodic ejection of plasmoids to balance the mass being added to the magnetosphere by Jupiter’s moons is termed the Vasyliunas-cycle. Rather than being formed by multiple x-line reconnection in a highly thinned current sheet, these Vasyliunas-cycle plasmoids are thought to form when a single X-line disconnects a highly stretched closed flux tube and allows its momentum to carry it down the tail. Due to the limited single-spacecraft measurements obtained by Galileo in the dusk-side magnetosphere, relatively little is known about these Vasyliunas-type plasmoids. Signatures of most Jovian plasmoids and flux ropes lasted ~6.8 minutes on average (Vogt et al., 2014), corresponding to diameters larger than 1 Jovian radii (RJ); much larger than the ion inertial length expected in the outer magnetosphere. Potential flux ropes on the ion-inertial scale, which would typically last for less than a minute could not have been identified using the Galileo magnetometer owing to the low cadence of several seconds per vector measurement. As part of its 53-day orbits, Juno spent a considerable amount of time in the dawn-side magnetotail. Using the high-resolution data from the Juno magnetometer, we identified two potential ion-scale flux ropes in the Jovian magnetotail by searching for bipolar variations in the magnetic field component normal to the current sheet. The two events were 22 s and 62 s in duration and were located at radial distances of roughly 74 RJ and 92 RJ between 03 and 04 local time. Assuming that the travel speed of the flux rope is limited by the Alfven speed in the surrounding magnetotail lobes, which is calculated using the plasma density inferred by the cutoff for the continuum radiation detected by the Waves instrument (0.003 to 0.012 cm-3), we estimated the diameters of these flux ropes to be 0.14 and 0.19 RJ respectively. The flux ropes’ diameters were comparable to the ion inertial length during these intervals, which was roughly between 0.11 to 0.23 RJ, (assuming a mass of 16.6 amu for the average ion). The selected events were analyzed using the minimum variance analysis and both events were seen to possess a strong core field with relatively high eigenvalue ratios, indicating that the MVA coordinate system was well-defined. Using a force-free model which is fitted to the observations, it was found that the flux ropes are quasi-force-free. These are the first reported observations of ion-scale flux ropes in the Jovian magnetotail. Although the large-scale dynamics of the magnetosphere may be dominated by the Vasyliunas cycle, the observations show that small-scale flux ropes, which are likely generated due to the tearing instability in a thin current sheet, also exist in the Jovian magnetotail, similar to the magnetotails of Earth and Mercury.

Abstract The long‐standing “energy crisis” at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin‐Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar‐wind‐magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune.

Charles Bowers, James Slavin, Gina DiBraccio, Gang Kai Poh, Shaosui Xu, David Brain, Jared Espley, and David Mitchell Department of Climatology and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA (@umich.edu) NASA Goddard Space Flight Center, Greenbelt, MD, USA (@nasa.gov) University of California, Berkeley, CA, USA (@berkeley.edu) Laboratory of Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA (@colorado.edu