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Ultra Low Frequency (ULF) waves with periods of 10–1,000 s can lead to space weather impacts such as induced electrical currents in power grids, thus it is important to understand the factors controlling wave dynamics. This is challenging, however, as waves (1) are affected by multiple factors simultaneously, (2) are non-stationary which in some cases precludes use of identification methods that assume stationarity, (3) can occur in superposition with each other making them difficult to separate and identify. Past studies have addressed these challenges through combined audiovisual analysis tools to identify complex but recurring patterns in ULF wave activity that eluded standard visual inspection and automated detection algorithms, as well as through crowd-sourced wave identification. The “Heliophysics Audified: Resonances in Plasmas” NASA citizen science project follows these studies by deploying a Graphical User Interface (GUI) for crowd-sourced ULF wave identification to a large online audience before and during the Heliophysics Big Year (HBY). In this study, we discuss the initial development, beta testing, and deployment of the GUI in April 2023. We further discuss the key initial scientific findings of the HARP project, in particular the discovery by volunteers of anomalous standing Alfvén wave activity with frequency increasing with distance from the Earth. Finally, we discuss participant impacts and lessons learned, as well broader impacts beyond the scope of the original project such as collaborations with museums and musicians. We place these results in context with previous work and discuss implications for future studies. 

Abstract Dawnside auroral polarization streams (DAPS) are fast eastward flows in the dawn convection cell of Earth's ionosphere. With a steep flow gradient near the interface between Region 1 and 2 currents and a peak poleward of it, DAPS were suggested to be responsible for instabilities and dramatic events in the magnetosphere‐ionosphere (M‐I) system. To predict these events, it is important to investigate when and where DAPS prefer to occur and how they are related to other M‐I phenomena. We conduct this investigation statistically using 10 years of Swarm data and find that DAPS under sunlit and dark ionospheric conditions exhibit different dependencies on magnetic local times and geomagnetic activities, reflecting a complicated interplay between magnetotail dynamics and ionospheric conductance. The statistical results also reveal a strong correlation between DAPS and embedded Region 2 currents. These findings provide new insights into the DAPS generation mechanism. 

Abstract Electron precipitation by chorus whistler‐mode waves generated by the same electron population is expected to play an important role in the dynamics of the outer radiation belt, potentially setting a hard upper limit on trapped energetic electron fluxes. Here, we statistically analyze the relationship between equatorial electron fluxes and the power of mid‐latitude cyclotron‐resonant chorus waves precipitating these electrons, both inferred from ELFIN low‐altitude energy and pitch‐angle resolved electron flux measurements in 2020–2022. We provide clear evidence of a flux limitation coinciding with an exponential increase of precipitation. We statistically demonstrate that the actual inferred resonant wave power gains are well correlated with theoretical linear gains, as in the classical Kennel‐Petschek model, for moderately high linear gains and high fluxes. However, we also find a finite occurrence of very high fluxes, corresponding to resonant waves of moderate average amplitude, implying a softer, more dynamical upper limit than traditionally envisioned. 

Abstract Poleward boundary intensifications (PBIs) are one of the most common auroral disturbances and have been shown to play a key role in substorm dynamics. PBIs are commonly interpreted as the ionospheric signature of magnetotail reconnection, providing insight into X‐line evolution. While PBIs have been linked to ionospheric flow channels using line‐of‐sight observations, their two‐dimensional flow dynamics remain poorly understood. Using coordinated THEMIS All‐Sky Imager and SuperDARN observations, we present high‐resolution two‐dimension flows derived by the spherical elementary current systems (SECS) method in association with PBI morphology. AMPERE magnetic perturbation data are presented for one event to analyze the current system associated with a dawn‐cell PBI. Ionospheric flow channel observations are used to infer plasma inflow in the magnetotail, and our results show they play a determining role in PBI morphology, including spatial extent, number, and propagation. These results suggest that inflow properties strongly influence X‐line dynamics. 

Abstract The ion foreshock is very dynamic, characterized by various transient structures that can perturb the bow shock and influence the magnetosphere‐ionosphere system. One important driver of foreshock transients is solar wind directional discontinuities (DDs) that demagnetize foreshock ions leading to a local current. If this current decreases the field strength at the DD, a hot flow anomaly (HFA) can form. Recent hybrid simulations found that when the current increases the field strength at the DD, a compressional structure forms with enhanced density and field strength opposite to HFAs. Using MMS and THEMIS observations, we confirm this situation. We demonstrate that the current geometry driven by the foreshock ions plays a critical role in the formation. The initial gyrophase of foreshock ions, due to their specular reflection, determines whether they can cross the DD. When many of the foreshock ions cannot cross the DD and the local current they drive increases the field strength at the DD, the enhanced field strength inhibits more foreshock ions from crossing the DD, further enhancing the local current. This feedback loop promotes the growth of the compressional structure. Such foreshock ion‐driven compressional structures can result in dynamic pressure enhancements in the magnetosheath, leading to magnetosheath jets. Our study enables prediction of the location and formation probability of such compressional structures and their potential geoeffectiveness. 

Abstract Recent observations show very near‐Earth reconnection (∼8–13R_E) could efficiently power the ring current during the main phase of geomagnetic storms, but whether the recovery phase might be contributed remains unclear. During the recovery phase of the May 2024 major geomagnetic storm, intense auroral brightening and geomagnetic disturbances were observed at midnight, indicative of particle injections. Current wedges observed by mid‐latitude ground magnetometers around midnight suggest dipolarizing flux bundles (DFBs). The latitude of the auroral brightening was clearly lower than usual, suggesting near‐Earth reconnection (NERX) was closer to Earth than during substorms (∼20–30R_E). GOES‐18 at midnight detected magnetic field and plasma signatures consistent with DFBs, following an extremely thin current sheet likely compressed by strong upstream dynamic pressure. These results indicate NERX could have been close enough for resultant DFBs to penetrate geosynchronous orbit and contribute to the ring current during the recovery phase. This scenario deserves further examination in future. 

Abstract Although the effects of electromagnetic ion cyclotron (EMIC) waves on the dynamics of the Earth's outer radiation belt have been a topic of intense research for more than 20 years, their influence on rapid dropouts of electron flux has not yet been fully assessed. Here, we make use of contemporaneous measurements on the same ‐shell of trapped electron fluxes at 20,000 km altitude by Global Positioning System (GPS) spacecraft and of trapped and precipitating electron fluxes at 450 km altitude by Electron Losses and Fields Investigation (ELFIN) CubeSats in 2020–2022, to investigate the impact of EMIC wave‐driven electron precipitation on the dynamics of the outer radiation belt below the last closed drift shell of trapped electrons. During six of the seven selected events, the strong 1–2 MeV electron precipitation measured at ELFIN, likely driven by EMIC waves, occurs within 1–2 hr from a dropout of relativistic electron flux at GPS spacecraft. Using quasi‐linear diffusion theory, EMIC wave‐driven pitch angle diffusion rates are inferred from ELFIN measurements, allowing us to quantitatively estimate the corresponding flux drop based on typical spatial and temporal extents of EMIC waves. We find that EMIC wave‐driven electron precipitation alone can account for the observed dropout magnitude at 1.5–3 MeV during all events and that, when dropouts extend down to 0.5 MeV, a fraction of electron loss may sometimes be due to EMIC waves. This suggests that EMIC wave‐driven electron precipitation could modulate dropout magnitude above 1 MeV in the heart of the outer radiation belt. 

Abstract Electron cyclotron harmonic waves (ECH) play a key role in scattering and precipitation of plasma sheet electrons. Previous analysis on the resonant interaction between ECH waves and electrons assumed that these waves are generated by a loss cone distribution and propagate nearly perpendicular to the background magnetic field. Recent spacecraft observations, however, have demonstrated that such waves can also be generated by low energy electron beams and propagate at moderately oblique angles . To quantify the effects of this newly observed ECH wave mode on electron dynamics in Earth's magnetosphere, we use quasi‐linear theory to calculate the associated electron pitch angle diffusion coefficient. Utilizing THEMIS spacecraft measurements, we analyze in detail a few representative events of beam‐driven ECH waves in the plasma sheet and the outer radiation belt. Based on the observed wave properties and the hot plasma dispersion relation of these waves, we calculate their bounce‐averaged pitch angle, momentum and mixed diffusion coefficients. We find that these waves most efficiently scatter low‐energy electrons (10–500 eV) toward larger pitch angles, on time scales of to seconds. In contrast, loss‐cone‐driven ECH waves most efficiently scatter higher‐energy electrons (500 eV–5 keV) toward lower pitch‐angles. Importantly, beam‐driven ECH waves can effectively scatter ionospheric electron outflows out of the loss cone near the magnetic equator. As a result, these outflows become trapped in the magnetosphere, forming a near‐field‐aligned anisotropic electron population. Our work highlights the importance of ECH waves, particularly beam‐driven modes, in regulating magnetosphere‐ionosphere particle and energy coupling. 

Abstract The growth phase of the magnetospheric substorm is accompanied by the formation of a thin magnetotail current sheet, which is subsequently destroyed due to magnetic reconnection. The configuration and kinetic properties of this current sheet determine its stability and are important in the context of reconnection onset. This study focuses on the electron component of such thin current sheets. Observations in the near‐Earth magnetotail show that electrons are predominantly field‐aligned anisotropic. However, this anisotropy decreases as the current sheet becomes thinner. The observed isotropization cannot be explained by electron scattering, as anisotropy is provided by the subthermal electron population. We propose an adiabatic model for such isotropization based on observations from the Time History of Events and Macroscale Interactions during Substorms mission, and demonstrate that the inclusion of a self‐consistent electrostatic field (current sheet polarization) can explain the decrease in electron anisotropy. Our findings highlight the importance of the role of electron temperature anisotropy and current sheet polarization in regulating the magnetotail dynamics during the substorm growth phase. 

Abstract Disturbances in ionospheric Total Electron Content (dTEC) with frequencies of 1–100 mHz can be driven from above by processes in the magnetosphere and below by processes on the Earth's surface and lower atmosphere. Past studies showed the potential of dTEC as a diagnostic of magnetospheric Ultra Low Frequency (ULF) wave activity and demonstrated that ULF dTEC can impact space weather by, for example, changing ionospheric conductance. However, most past work has focused on single event studies, lacked magnetospheric context, or used sampling rates too low to capture most ULF waves. Here, we perform a statistical study using Time History of Events and Macrsoscale Interactions during Substorms (THEMIS) satellite conjunctions with a ground‐based magnetometer and Global Navigation Satellite System (GNSS) receiver at 65° magnetic latitude. We find that magnetospheric ULF waves generate dTEC variations across the broad range of frequencies examined in this study (2–50 mHz), and that ULF dTEC wave power is correlated with Kp, AE, solar wind speed, and magnetic field wave power observed in the magnetosphere and on the ground. We further find that magnetospheric ULF waves generate dTEC amplitudes up to TECU ( background), with the largest amplitudes occurring during geomagnetically active conditions, at frequencies below 7 mHz, and at local times near midnight. We finally discuss the implications of our results for magnetosphere‐ionosphere coupling and remote sensing techniques related to ULF waves.