Space Physics

The dynamics of energetic electron fluxes in Earth’s radiation belts are conventionally described by two dominant mechanisms: (1) wave–particle resonant interactions, resulting in acceleration and pitch-angle scattering, and (2) radial diffusion driven by ultra-low-frequency (ULF) waves. However, observations often reveal behavior that cannot be fully explained by these processes, indicating the need for additional radial transport mechanisms beyond classical diffusion. Indeed, radial transport can arise even in the absence of waves, solely due to the topology of magnetic field lines. This mechanism is known as Drift-Orbit Bifurcation (DOB), which occurs on the dayside, where solar wind compression splits the equatorial magnetic field minimum into two off-equatorial minima, violating the second adiabatic invariant and enabling radial transport. While previous studies have primarily considered symmetric magnetic field configurations, we conduct a detailed investigation of realistic DOB under north–south and east–west asymmetries introduced by the IMF direction and dipole tilt angle. We find that such asymmetric configurations produce large jumps—of the order of the adiabatic invariant itself—in the second adiabatic invariant. Moreover, we show that these jumps closely correspond to the so-called geometric jumps well known in Hamiltonian systems theory. Using a Hamiltonian framework and large-scale guiding-center simulations, we show that these jumps can drive substantial radial transport within a single drift period. We discuss the implications of this new radial transport mechanism in the context of energetic electron transport near the magnetopause. These results shed new light on observations of isolated enhancements of >30 keV electrons, as observed by equatorial spacecraft (THEMIS) as well as low-orbit spacecraft such as CubeSats (ELFIN/CIRBE) and POES.

Turbulence is an important mechanism for energy conversion in weakly collisional plasmas. In fluid turbulence, energy injected into the system at large spatial scales is transferred to smaller scales until it is dissipated as heat through collisions. In the interim between energy injection and dissipation, kinetic effects can also mediate the dissipation of energy below characteristic fluid (ion) scales. There is a longstanding question concerning plasmas with low collisional rates: How does this energy conversion process end without collisions? In addition, this classical understanding of turbulence is, in nature, based on a velocity-averaged theory of Vlasov-Boltzmann systems. The energy in consideration is that of the plasma bulk motion; the transfer process is one through space. Since a Vlasov-Boltzmann description concerns both space and velocity, we can also ask the question: Is there a conjugate spatial-averaged theory of turbulence, one that describes a turbulent energy transfer instead through velocity?
In this talk, we explore these two questions regarding turbulence in space and in velocity with MMS observations in two regions in the Earth’s magnetosphere. In the magnetotail, explosive large-scale magnetic reconnection generates strong turbulence with low density and background field. The electromagnetic field spectra are well resolved below electron scales, suitable for turbulence studies of kinetic effects. We show evidence of a sub-electron kinetic range where the energy transfer process appears to complete. In the magnetosphere, the distribution function is well resolved with MMS instruments, suitable for turbulence studies of fine structures in velocity space near fluid scales. We show the first ever statistical observation of velocity-space cascade using data from the MMS unbiased magnetosheath campaign

It has been established since the Helios epoch and confirmed by Ulysses and SOHO that the sources of fast solar wind streams at solar minimum are the polar coronal holes, while slower solar wind streams have contributions from different sources. The larger than expected filling factor of slow solar wind has been attributed to flows coming from coronal hole boundaries, i.e., regions with large expansion factors, or from regions where the mapping of the magnetic field from the photosphere into the heliosphere is complex, as identified for example by the squashing factor, and known as the S-Web.
The observations by Parker Solar Probe that much of the solar wind, independently of speed, is dominated by Alfvénic fluctuations, and the frequent observation of slow Alfvénic solar wind, previously observed relatively rarely in Helios and Wind data, provide evidence for a picture of solar wind origins that incorporates both the expansion factor and S-web paradigms: both coronal holes with large expansion and S-Web regions act as slow solar wind sources, with the difference that highly expanding coronal holes provide Alfv.nic slow streams, while the S-web wind is unlikely to exhibit strong Alfvénic correlations.
As far as the fast solar wind is concerned, we focus on a new aspect associated with the interaction of spherically polarized Alfvén waves and the background wind. It arises from the continuous presence of spherically polarized Alfvénic fluctuations, in the form of switchbacks and patches of switchbacks, that lead the solar wind to be formed of multitudes of one-sided jets. We call the average effect of such jets the Gosling boost, as Jack Gosling was the first to recognize such one-sided jets over the baseline unperturbed solar wind expansion. Here we show how the Gosling boost provides direct empirical evidence for the acceleration of the wind by Alfvénic fluctuations and discuss the more general question
of the origin and acceleration of Alfvénic solar wind streams.

Decades of spacecraft and telescope observations of Jupiter’s upper atmosphere reveal that plasma emissions, densities, temperatures and vertical structure do not appear to be controlled by sunlight alone. In this talk, I will present a recently developed unified picture in which neutral winds, acting along Jupiter’s spatially complex magnetic field via field aligned ion–neutral coupling, drive vertical transport that organizes the non auroral ionosphere and creates the steady spatial patterns seen in ~60 years of observations.

This unified view has been informed by 5 complementary studies: a reanalysis of ~6 decades of spacecraft radio occultations (Pioneer, Voyager, Galileo, Juno) which reveal significant variability in plasma vertical structure; over 175,000 spectra from ground-based telescopes (KECK/NIRSPEC), collected across four years, that produce high resolution global maps of ion densities and temperatures; a coordinated 2023 campaign (Juno, JWST, Keck) that delivered simultaneous continuous electron and ion vertical profiles; a new general circulation model of Jupiter’s thermosphere (JTIM) and ionosphere, which produces the first global wind maps consistent with observed temperatures; and a novel Jovian ionosphere model (JAMMIES) which includes an approximation of Jupiter’s magnetic field geometry and can reproduce various observed phenomena through its comprehensive treatment of ionospheric transport at Jupiter.

Finally, I will briefly discuss the outstanding mysteries still persist, concerning how such an ionosphere feeds back on magnetospheric currents, and the unknown drivers that control ionospheric dynamics in regions where neutral wind control is weak.

On May 10, 2024, the Earth’s geospace system and existing models were pushed to their limits by the largest geomagnetic storm in two decades. While the resulting auroras were a global spectacle, the underlying physics revealed a system undergoing a rapid and large-scale structural reconfiguration. This talk explores the science of this extreme event across the whole geospace system, emphasizing how the ionosphere responded to these unique drivers. By examining the magnetospheric and upper atmospheric responses together, the complex coupling and energy exchange between these regions become clearer. These observations demonstrate the necessity of a coupled whole geospace approach to analyze how these systems communicate and what happens when that global conversation turns into a shout.
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Accurately diagnosing and characterizing plasma dynamics in laboratory experiments and space plasmas is essential for advancing basic plasma science. Modern high-repetition-rate
experiments and multi-spacecraft missions provide increasingly rich spatiotemporal measurements, but computational tools that can fully exploit sparse, noisy, and incomplete data
remain lacking. Physics-informed neural networks (PINNs) offer a promising route by combining partial measurements with fundamental plasma equations to reconstruct physically
consistent quantities that were not directly measured.
In this talk, I will illustrate this approach using shear Alfvén waves, a fundamental mode of magnetized plasma that transports electromagnetic energy along magnetic fields and is relevant
to auroral energy flow [1]. Using synthetic magnetic-field measurements from fully kinetic particle-in-cell simulations, we show that PINNs can reconstruct the full two-fluid plasma
state—including electric fields, ion and electron velocities, and density perturbations—from sparse magnetic-field data alone. The method achieves approximately 10% relative accuracy
under adequate sampling and remains robust to substantial measurement noise.
I will then discuss first applications to experimental measurements of shear Alfvén waves on the Large Plasma Device at UCLA [2], including challenges posed by real data. Finally, I will briefly
outline how this framework could be extended to multi-spacecraft observations, where detailed measurements of the magnetic-field and the plasma distribution function are available but very
sparse.

Parker Solar Probe is revolutionising our understanding of turbulence in the solar wind and corona. The “standard model” of anisotropic, low-frequency Alfvénic turbulence predicts little ion heating, because the magnetic moment is conserved to all orders in the low-frequency expansion. This is in stark contrast to the observed dominance of perpendicular ion heating in the corona and low-beta solar wind.
In this talk, I present a new theoretical picture of perpendicular ion heating that unifies previous models of stochastic heating, cyclotron heating, and heating in guide-field reconnection. An important advantage of this new model is that it is easy to apply to intermittent turbulence. I demonstrate that accounting for rare, large-amplitude coherent fluctuations, naturally produced by the turbulent dynamics, can dramatically enhance the predicted efficiency of ion heating, resolving the previous discrepancies between theory and space measurements. This suggests that intermittency is not just a statistical curiosity, but a necessary component of any theory purporting to describe heating in plasma turbulence.

Large language models, and the agents built on top of them, are beginning to change how research is done, yet the core ideas remain unfamiliar to many scientists. In this talk, I will explain them from the ground up, assuming no prior background: what a large language model is, what an AI agent is, and what an “agent harness” — the tools, memory, and feedback loop that turn a passive model into something that can act — actually does. I will then turn to why this matters for Earth and space sciences, where reaching a scientific result often means first spending months learning each mission’s data formats and conventions, and describe an effort to build a shared, community-owned skill repository that lets agents handle this competently across subfields. The broader argument is that agents are poised to transform not only everyday scientific work but how people work more generally — and that building the right scaffolding now is what determines whether that promise is realized.

The eleven-year solar activity cycle manifests itself in a variety of spectacular and interdependent ways. For example, the spatiotemporal distribution of the emergence of bipolar active regions (ARs) impart a spatiotemporal dependence to the response and re-configuration of overlying large-scale, closed-flux helmet streamer belt. Additionally, specific AR–background field configurations can arise that form new, intermediate-scale closed-flux systems surrounded by single polarity open fields, such as coronal pseudostreamers, which also inherit the underlying solar cycle-dependence of their photospheric flux distributions. The global magnetic structure of the solar corona, in turn, determines the entire solar wind stream and magnetic sector structure of the inner heliosphere. The cusp region of the coronal helmet streamer belt extends into a dense, slow solar wind plasma sheet that contains the heliospheric current sheet (HCS), separating the open fields of opposite polarity. The equivalent heliospheric extension of pseudostreamer outflows along the outer spine-line or spine-fan, result in slow, plasma-sheet like solar wind embedded in a single open field polarity.
In this talk , I will present an overview of the ways in which coronal magnetic field topology, open-closed flux system boundary layers, and their dynamic evolution can determine the resulting solar wind properties and structure of the inner heliosphere. As an illustrative example, I will discuss recent remote-sensing and in-situ observations made by Parker Solar Probe (PSP) in the context of the Casillas et al. [2026] magnetohydrodynamic simulation results. For example, the PSP Encounter 24 observations appear to have captured certain aspects of the Casillas et al. scenario of a global-scale pseudostreamer–to–helmet streamer transition and the generation of outflow transients associated with the opening-up (and closing-down) of a large-scale pseudostreamer flux system which creates (or destroys) the parasitic-polarity solar wind streams and their associated HCSs.

Magnetopause magnetic reconnection during periods of northward interplanetary magnetic field (IMF) plays a key role in the entry of solar wind mass into the magnetosphere. The effects of reconnection can be observed in the low-altitude cusp, and the new NASA TRACERS mission is designed for this purpose. I will present a TRACERS-THEMIS conjunction near the peak of a geomagnetic storm after the IMF had turned northward. In the low-altitude cusp, TRACERS observed signatures consistent with lobe reconnection poleward of the cusp, including reversed ion dispersions and sunward convection. Concurrent THEMIS observations at the low-latitude magnetopause reveal the presence of a magnetosheath boundary layer (MSBL) and capture of magnetosheath plasma on magnetospheric field lines, both consistent with poleward-of-cusp reconnection. Global simulations of the event show that poleward-of-cusp reconnection was adding magnetic fields and plasma to the magnetosphere, and in the process moving the cusp poleward. The event also illustrates how the magnetosphere and cusp recover when the IMF turns northward after a storm has eroded the magnetopause inward and moved the cusp equatorward.

Jupiter’s moon Europa is a key target in the search for extraterrestrial life, but assessing its habitability via magnetic induction requires a well-grounded understanding of the plasma environment. At Europa, this task relies on magnetohydrodynamic (MHD) models that have been developed over many years. While powerful, these models are computationally expensive, with some codes requiring > 12 hours on a 2,000-core machine. Fitting spacecraft observations to MHD models demands many runs, resulting in a potentially days- or weeks-long process. This presents a major bottleneck for missions such as Europa Clipper and JUICE, potentially limiting their scientific return.
In this talk, I introduce a transformer-based surrogate for a state-of-the-art MHD model used to help characterize Europa’s subsurface ocean. The surrogate evaluates in milliseconds on a laptop rather than hours on a supercomputer, achieving a speed-up of approximately 40,000x while delivering high-fidelity, uncertainty-aware magnetic field predictions. This acceleration enables three new scientific pathways that are feasible with MHD alone: large-scale parameter surveys, simulation-based inference, and feature-importance analysis. These analyses are important as the environment is poorly constrained observationally. Overall, this approach represents a paradigm shift in the investigation of space plasmas and opens the door to a host of novel science investigations.

NASA science missions are often complex systems of systems, involving various stakeholders, including the United States’ Congress. To ensure a clear and concise communication of expectations, requirements, and constraints, NASA has adopted the Science Traceability Matrix (STM). STM provides a logical flow from the decadal survey to science goals and objectives, mission and instrument requirements, and data products. STM serves as a summary of what science will be achieved and how it will be achieved, with a clear definition of what mission success will look like. In this seminar, I will present the STM from the Parker Solar Probe (PSP), including requirements relating to the plasma instrument for which I am a co-investigator. I will describe how our team used the STM to map the mission’s top-level requirements to mission success criteria and helped to eliminate any single point of failure that could end the mission prematurely. I will then present my own research on magnetic switchbacks in the PSP magnetic and plasma observations and their role in solar wind acceleration and heating. I will conclude the seminar by discussing how my research on the temporal evolution of switchbacks in the solar wind led to a new STM, and helped to chart a multidisciplinary path to designing a ground-breaking science mission concept, titled Space Weather Investigation Frontier (SWIFT), with the potential to improve space weather forecasting lead times by up to 40%.

Extraterrestrial EM induction was first carried out in the 1970s
by forming magnetic transfer functions for the Moon as the ratio of
magnetic fields observed at the surface (Apollo 12) to those observed in
distant orbit (Explorer 35). In March 2025, a similar analysis was
performed using the Lunar Magnetotelluric Sounder (LMS) on Blue Ghost
Mission 1 and the ARTEMIS spacecraft. In spite of nearly 90 deg arc
distance between these surface locations, the derived subsurface
conductivities are very similar. This sharply limits contemporary
temperatures under the western nearside of the Moon in spite of its past
history of widespread volcanism. The two-week surface mission recorded
surface electric and magnetic fields in the solar wind, magnetosheath, and
magnetotail, including an eclipse and sunset. Plasma properties correlate
well with ARTEMIS.

Mars’ lack of a global magnetic field led to low expectations for auroral phenomena on the planet, but MAVEN and Emirates Mars Mission observations have unexpectedly shown auroral activity to quite diverse in nature, dynamically varying and often global in scope. The image below shows three fundamentally different types of aurora on Mars. Ironically, Mars’ lack of a global field is actually responsible for most of the activity, which leads to a new perspective for non-magnetized objects in our solar system and beyond. Each of the three types of aurora is a tracer of a different important process involving the interaction between solar influences and the near-Mars magnetic and charged particle environment. The seminar will describe observations by MAVEN’s Imaging UltraViolet Spectrograph (IUVS) and the Emirates Mars UltraViolet Spectrometer (EMUS) and highlight the new insights they offer.

Space weather is the “weather” of the space environment driven by our active Sun—solar eruptions and changing solar wind conditions that can disturb Earth’s magnetic field and upper atmosphere, disrupt satellites and communications, degrade navigation and timing, increase radiation risk to astronauts, and induce electrical currents in long conductors on the ground. Over the past decade, U.S. preparedness for major space weather events has changed in two consequential ways: (1) the power sector began translating scientific risk into enforceable reliability practice when the Federal Energy Regulatory Commission (FERC) directed the North American Electric Reliability Corporation (NERC) to develop Reliability Standards to mitigate geomagnetic disturbance (GMD) impacts on the Bulk-Power System ; and (2) the United States adopted a coordinated, whole-of-government posture through the National Space Weather Strategy and Action Plan—now further advanced through a more recent federal implementation plan that builds on the 2015 foundation .

I will highlight key scientific and operational developments from the last few years, including NASA’s Space Weather Program role in advancing space weather observations, models, and applications that support prediction and tracking across the solar system. A central case study will be the May 2024 geomagnetic storm—first G5 (“severe”) storm in over two decades—now commonly referred to as the “Gannon storm,” and what it revealed about magnetosphere–ionosphere coupling, satellite impacts, and the pathways to societal consequences.

Finally, I will offer focused perspectives on high-impact risk areas—especially electric power grids—connecting space physics to practical resilience: where the key areas of uncertainty are, what “good enough” information looks like for operations, and how research, standards, and planning can converge to reduce national risk before the next extreme event.

Learn about ionizing radiation in the final frontier from UCLA Space Medicine Program Director Dr. Haig Aintablian and Radiation Oncology resident Dr. Nic Nelson. They will share a brief overview of modern space medicine and basic radiobiology before exploring the space radiation environment with its unique risks to astronaut health. They will then illustrate how researchers and mission planners are preparing for the next phase of human space exploration—interplanetary travel—by investigating different physical and biological countermeasures and applications in personalized medicine.

Solar radio bursts are signatures of nonthermal electron acceleration by energetic events such as flares and coronal mass ejections. The launches of Parker Solar Probe in 2018 and Solar Orbiter in 2020 have enabled new views of radio bursts from the vantage point of the inner heliosphere. In this talk, I will briefly discuss some of the top radio burst discoveries of the Parker-Orbiter era, with a focus on circular polarization observations made by Parker Solar Probe. I will describe the measurement of polarization using spacecraft antennas, show examples of circularly polarized Type II and Type III radio bursts, and discuss how polarization can serve as a remote diagnostic of radio burst source regions.

Galileo, Cassini and Juno space missions have provided much data on gas giant magnetospheres. Here we examine the important commonalities of the two systems that also characterise the differences to the plasma environment of the inner planets. Both systems are fast rotators and have internal sources of magnetospheric material deep within the system. The internal sources means there must be a system for transport of material outward. Commonly, marginally stable interchange motions of flux tubes are invoked to provide diffusion on relatively small scales transverse to the field. This no doubt occurs near the source but processes like self-organisation may lead to more ordered motion at larger distances. A large distinction between Jupiter and Saturn systems is that the jovian planetary magnetic field is far from axially symmetric with respect to the planetary rotation axis whereas Saturn’s field is close to axially symmetric. However, despite this, the Saturn system does exhibit variable periodicities in plasma, radio, aurora and the external magnetic field around 10.7 hours. The external magnetic source was a surprise; the ubiquitous Saturn oscillations are still described as “mysterious”. No similar oscillations are recorded at Jupiter. We shall aim to remove some of the mystery and suggest that the dynamical effect of rotation has not been fully appreciated in either system.

Prediction serves as the ultimate test of our scientific understanding of geophysical systems. Accurate forecasting of near-Earth space environmental conditions is critical to radio communication, navigation, and space traffic management. Effective numerical prediction of the region’s conditions allows us to better protect important space assets and related systems in the event of natural hazards. My research group aims to advance the science and engineering of forecasting, as applied to the Earth’s atmosphere extending from the ground to geospace. Prediction of the constantly changing near-Earth space environmental conditions – affected by both space and terrestrial weather – is inherently challenging. Data assimilation provides a systematic approach to integrating observations with first-principles models, extending the predictive capability of numerical models by reducing uncertainties in drivers and preconditions and constraining model dynamics with observations. The data assimilation and ensemble-based probabilistic modeling framework can also be applied to the design of future missions and the targeting of observations to maximize scientific returns of observing systems. This seminar showcases some of the latest data assimilation research and outlines future plans, setting the stage a discussion on how we can work together to advance the next generation of predictive modeling and observational strategies.

Mars’ interaction with the solar wind exhibits a hybrid nature. The Martian magnetosphere, formed through interactions between the solar wind, ionosphere, and crustal magnetic fields, is complex and highly dynamic. While largely induced, it also contains localized regions where strong crustal fields dominate plasma dynamics. Global magnetohydrodynamic (MHD) modeling has become a critical tool for investigating this system and its role in atmospheric escape. Multi-species MHD studies first demonstrated the importance of ion-specific treatment at high spatial resolution, while later work revealed how rotating crustal fields modulate plasma boundaries and ionospheric structure. Applications to extreme events, such as the September 2017 ICME and the December 2022 disappearing solar wind event, highlighted the dynamic response of Mars’ plasma environment to solar wind variations, particularly density changes. This seminar will review advances in global MHD modeling of Mars and discuss their implications for understanding atmospheric escape and developing future space weather forecasting capabilities at the planet.

The Polarimeter to Unify the Corona and Heliosphere (PUNCH) is a constellation of four smallsats launching in Spring 2025 to image the solar corona and solar wind as a single unified system. The four satellites work together to form a single “virtual coronagraph” with a 90° field of view centered on the Sun. One satellite carries a coronagraph (the Narrow Field Imager) that captures the outer corona at apparent distances between 6 solar radii and 32 solar radii from the Sun. The other three carry heliospheric imagers with 42° wide fields of view, extending from 12 solar radii to 180 solar radii from the Sun. All instruments view visible light scattered by free electrons in the corona and solar wind and use linear polarization to generate 3D information about density structures in the plasma. In this talk, I will briefly describe some of the key background science and the mission itself, then discuss the enabling technologies of deep signal separation and polarimetric inversion to reveal 3D structure before presenting and discussing recent data from the constellation and how to obtain the data for your own use.

Space is never empty. Instead, it is filled with high-energy particles originating at the Sun and trapped by Earth’s magnetic field, forming dynamic radiation environments that pose significant risks to satellites, astronauts, and future exploration missions. In this talk, I will discuss the evolution of Earth’s radiation belts during geomagnetic storms, the processes that limit their intensity, and how similar processes may operate under artificially created conditions. I will present recent work on fast plasma processes that substantially alter radiation levels around Earth. My approach integrates data analysis, simulations, and the development of advanced particle detectors derived from technology originally designed at CERN, tailored specifically for space missions. Additionally, I will showcase results from a student-led balloon mission conducted during the most intense geomagnetic storm of the past two decades. 

Earth’s outer radiation belt is a doughnut-shaped region in space, containing stably trapped energetic electrons. Its outer boundary is closely related to the electron isotropy boundary (IB), which separates the outer radiation belt from the isotropic, precipitating electrons found further out, in the tail current sheet. Field-line curvature scattering (FLCS) is believed to play an important role in causing this isotropic electron precipitation and is effective when the electron gyroradius becomes comparable to the field line curvature radius in the equatorial current sheet region. However, the direct and quantitative impact of FLCS in controlling the outer belt electron lifetimes has never been directly assessed. In this talk, I will discuss the role of FLCS in controlling the outer belt electron lifetimes by combining observations and global radiation belt electron simulations. I will also reveal that this simple yet fundamental physical process which has been historically neglected in global radiation belt models, is sufficient to explain the outer electron belt configuration. Our findings transform our understanding of the dominant processes controlling radiation belt dynamics.

Jupiter’s moon Europa is thought to possess a subsurface ocean that could have the right conditions to harbor life. It will be visited by the Europa Clipper mission starting in 2030. To characterize this ocean and answer questions about habitability, the complex and highly variable plasma environment must be accounted for. In this talk, I will introduce a novel machine learning framework, including both forward and inverse modeling, to better understand the environment. Crucially, our model can reproduce the magnetic field, helping us define the depth, salinity, and conductivity of a potential subsurface ocean. These findings benefit both the upcoming missions to Europa and proposed missions to other planetary bodies such as those at Uranus or Neptune.

Magnetic reconnection occurs continuously along long X-lines at the Earth’s magnetopause. The maximum magnetic shear model provides accurate predictions for the locations of these long X-lines for a wide range of upstream solar wind conditions. One of the more perplexing observational results is that these X-lines appear to be stationary, even on the near-flank magnetopause in the presence of significant magnetosheath plasma bulk flow. An alternate possibility is that X-lines form in the location predicted by the maximum magnetic shear model but then immediately propagate with the magnetosheath plasma bulk flow away from this location. If the X-line reformation cadence is high enough and some other conditions are valid, then these multiple propagating X-lines could appear as a single quasi-stationary X-line at the location predicted by the maximum magnetic shear model. Magnetospheric multiscale observations are used to perform initial tests of this alternate possibility. Results from these initial tests show that there may be multiple X-lines near the predicted location of the X-line, and therefore this alternate possibility may have merit. This alternate possibility may have implications for the magnetospheric cusps. Magnetic reconnection at the magnetopause produces distinct energy-latitude ion dispersion features in the cusps. Multiple reconnection X-lines may produce overlapping dispersion features depending on how they are formed. Therefore, under the right solar wind conditions, there may be many instances of overlapping dispersion features. Observations from the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) are used to investigate this possibility.

Magnetosphere and ionosphere coupling is largely driven by electromagnetic waves (e.g., Alfven waves) and particle precipitation in the polar cusp and auroral region. This coupling is inherently dynamic, nonlinear, and multiscale. Ionosphere magnetic perturbations (δB) span scales from >1,000 km across the auroral zone—associated with Region-1 and Region-2 field-aligned currents (FACs)—down to <1 km, approaching the electron inertial length and corresponding to fine-scale auroral arcs (~100 m). These smaller scale δB are often linked to inertial Alfven waves that carry parallel electric fields, accelerate electrons, and produce dynamic auroral structures. During geomagnetic storms and substorms, transient currents associated with these small-scale δB can exceed several hundred μA/m2, leading to ionosphere total electron content (TEC) perturbations and plasma irregularities that cause GPS scintillations and disrupt communication. Characterizing these small-scale δB and their space weather effects remains challenging due to Doppler shift from spacecraft motion (~7.8 km/s) and the scarcity of tandem spacecraft observations of electric and magnetic field measurements necessary to distinguish DC and wave components. NASA's TRACERS mission, launched on 24 July 2025, offers new opportunities to investigate these processes. Here we present initial results from TRACERS MAG observations of a coincident small-scale δB and GPS scintillation event.

The Low-Latitude Ionosphere/Thermosphere Enhancements in Density (LLITED) mission consisted of two 1.5U CubeSat to study nighttime ionosphere/thermosphere coupling. Each CubeSat hosts three science payloads: an ionization gauge (MIGSI) to observe neutral density, a planar ion probe (PIP) to observe plasma density, and a GPS radio occultation sensor for observing (CTECS-A) total electron content. The overall mission, from proposal to on-orbit operations and science investigations, has presented a number of challenges often requiring difficult decisions and compromise in order to maximize the science returns. The various orbit and technical difficulties necessitated a modification and reprioritization of LLITED’s science mission objectives. By modifying the mission science goals, prioritizing event-associated observations, and combining data from other missions and observational conjunctions, LLITED provided insightful observations of neutral and plasma density structures and coupling. This presentation will provide an overview of LLITED’s datasets, describe the various on-going studies, and highlight observations of neutral and plasma density structures at high and mid- latitudes, as well as observations of short time stability of small-scale density structures.

Alfvén waves, named after the Nobel laureate Hannes Alfvén, are a fundamental mode in magnetized plasmas. It has long been established that they play a key role in the energy circulation of the magnetosphere-ionosphere (M–I) coupling system. However, their dissipation on meso- and small-scales is much less well understood. Here, we examine how Alfvén waves drive several common meso-scale structures, including the auroral arcs, auroral beads, and the magnetospheric cusp. We find that Alfvén waves, although being the common energy source, are dissipated differently among these structures. In the auroral arcs, Alfvén waves power a quasi-static parallel electric field that accelerates ions away from and electrons toward the ionosphere. In the auroral beads, electrons are accelerated directly by the wave’s own parallel electric field. In the cusp, Alfvén waves significantly energize the outflowing ions, presumably through perpendicular heating. These distinct energy conversion processes we have unveiled are important in understanding the meso-scale M–I coupling on Earth and other planets. Our results also raise important questions for future studies: How are these Alfvén waves generated? What additional dissipation mechanisms may be operating? Why are Alfvén waves dissipated differently, and what are the controlling factors?