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.