Journal of Geophysical Research: Space Physics最新文献

During the September 2019 geomagnetic storm, long-lasting, drift-periodic flux oscillations of multi-MeV electrons were observed by the REPT instrument on the Van Allen Probes–A. These flux oscillations occurred across the outer belt during the storm main phase, coinciding with enhanced Pc5 ULF wave activity and elevated electron fluxes. During the recovery phase, the oscillations gradually decayed at the center of the outer belt but persisted for days at its inner edge. Using 2D test particle simulations driven by constructed broadband ULF wave fields, we simulated multi-MeV electron fluxes during two satellite passes and successfully reproduced observed drift-periodic flux oscillations. The close agreement between simulation and observation confirms a causal relationship between drift-periodic flux oscillations and resonant interactions of electrons and broadband ULF waves. We further derived the radial diffusion coefficient from the simulation and compared it with empirical models. The magnitude of the resultant radial diffusion coefficient aligns closely with the model by Liu et al. (2016, https://doi.org/10.1002/2015gl067398), though it is lower than those by Brautigam and Albert (2000, https://doi.org/10.1029/1999ja900344) and Ozeke et al. (2014, https://doi.org/10.1002/2013ja019204). The energy- and L-dependence of the diffusion coefficient is also consistent with the model by Liu et al. (2016, https://doi.org/10.1002/2015gl067398). We estimated the uncertainty in the derived radial diffusion coefficient to be approximately half an order of magnitude, primarily limited by the instrument's energy resolution. These results demonstrate the potential of inferring radial diffusion rates from electron flux measurements alone and underscore the importance of high-energy-resolution electron measurements for accurately quantifying radiation belt dynamics.

Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) simulations are used to investigate the thermospheric and ionospheric day-to-day variability caused by the upward propagating migrating diurnal (DW1) and semidiurnal (SW2) tides under conditions with constant solar and geomagnetic forcing. In the lower thermosphere, tidal dissipation deposits momentum and energy, causing significant variability in neutral winds and temperature of ∼20 m/s and ∼5 K for DW1, and ∼40 m/s and ∼20 K for SW2. DW1 and SW2 lead to an overall global reduction of the ratio of column integrated atomic Oxygen to molecular Nitrogen (ΣO/N₂) and an increase in ΣO/N₂ day-to-day variability. DW1 and SW2 also exert a significant impact on the equatorial electrodynamics, which leads to variations in ionospheric total electron content (TEC). The ΣO/N₂ day-to-day variability is small (∼1.5%), and DW1 and SW2 contribute ∼10% and ∼20% to this day-to-day variability. In contrast, the TEC day-to-day variability is much larger (∼20%), with DW1 and SW2 contributing ∼20% and ∼40%, respectively. The wind variations caused by DW1 and SW2 exhibit different vertical wavelengths of ∼30 and ∼60 km in the lower thermosphere, but are nearly infinite in the upper thermosphere. The large tide vertical wavelengths in the upper thermosphere are caused by dissipative processes in the thermosphere. Our results demonstrate that the effects of upward propagating DW1 and SW2 on TEC are comparable on day-to-day and seasonal scales, but for thermospheric ΣO/N₂, their impact on the day-to-day scale is significantly weaker than that on the seasonal scale.

Enceladus's south polar plumes and their surrounding torus segments (local plasma regions formed by plume material diffusion) are key to understanding its magnetospheric interaction; however, clear observational criteria to distinguish them remain lacking. We analyze data from 23 Cassini flybys (2005–2015), including magnetic field, energetic particle, and wave measurements. Plumes are characterized by localized magnetic perturbations (ΔB > 10 nT), sharp electron and ion density spikes (with n_e < n_i), intense energetic particle absorption (exceeding one order of magnitude), and the presence of ice grains and neutral species. The local torus segments show weak ΔB (2–5 nT), gradual density changes (n_e ≈ n_i), and mild particle absorption (less than one order of magnitude). These criteria advanced our understanding of Enceladus' plume-related material transport. This framework can be adapted to Io/Europa observations by rescaling thresholds to local magnetospheric conditions.

We present the new probabilistic model of the electron fluxes designed to assess the risks of the spacecraft surface charging for missions with near-equatorial orbits in the inner magnetosphere. It is a second model developed within a frame of the European Space Agency's activity “Plasma Environment Modeling in the Earth's Magnetosphere” (PEMEM). The first model PEMEM Percentile (Dubyagin et al., 2024, https://doi.org/10.1029/2023JA032026) has a robust though somewhat simple functionality. Addressing the PEMEM Percentile weaknesses, we test a novel approach to incorporating the dependence on geomagnetic activity in probabilistic models. The model is based on Van Allen Probes particle data. The model is driven by the auroral electrojet (AE) index from a period in the past corresponding to the expected solar cycle phase during a mission lifetime. The main model inputs are the spacecraft orbit, the time interval of AE-index to drive the model, and the confidence levels. For given confidence levels, the model outputs the worst-case 1–100 keV integrated electron flux and corresponding differential flux spectrum. The model can output these parameters separately for the eclipse and sunlit parts of the orbit. While investigating the response of the electron flux to the AE-index variations, we have found that lower energy electrons reveal the highest correlation with the AE-index averaged over the substorm time scale, while higher energy electrons show a higher correlation with AE on the storm time scale. The transition between these two regimes occurs at $��\sim �30�$ keV energy and has a complex dependence on radial distance and MLT.

The Wideband Data instrument is part of the Cluster spacecraft Wave Experiment Consortium. Its primary data path is a direct connection to the spacecraft data handling system providing real time downlink to the ground stations of the Deep Space Network and Panska Ves Observatory. However, it was recognized during the mission design phase that this link may not always be available, especially given that simultaneous data acquisition from the four Cluster spacecraft required the use of four ground stations. Therefore, a secondary data path at reduced bit rate was included whereby the data was transferred to the Digital Wave Processor instrument and then to the spacecraft Solid State Recorder. Given that available resources were limited, both for onboard hardware and within the spacecraft assembly, integration and testing program, the design of this backup data path was less than optimal. Although it was verified during ground testing that data could be acquired via this route, the design did not make the best use of the available telemetry bandwidth, and the timing accuracy was too limited to support some multi-spacecraft observations. This paper describes work around solutions to optimize bandwidth utilization and timing accuracy. These involve patches to the onboard software of the Digital Wave Processor instrument and ingenious signal processing on the ground.

Dipolarization fronts (DFs), ion-scale magnetic-dipolar transients in the magnetotail, are favorable regions for the generation of various types of plasma waves, which are important for energy transport and dissipation in the magnetosphere. The plasma waves hitherto reported near the DFs are typically low-frequency (lower than electron cyclotron frequency) modes. Here, we report MMS observations of high-frequency waves, including Langmuir and upper hybrid waves near the electron plasma frequency, inside flux pileup regions behind the DFs. Using MMS high-cadence data, we revealed that the Langmuir waves were possibly generated by local electron beams and rapidly thermalized the beams, and the upper hybrid waves, which were associated with perpendicularly anisotropic electrons, may propagate from other regions. These waves can drive localized energy transfer and accelerate local electrons at a rate of ∼1.5 eV/s, indicating that the high-frequency waves can play a role in wave-particle energy transfer near the DFs.

High-speed jets (HSJs) are transient phenomena characterized by significant enhancement of magnetosheath dynamic pressure. They are capable of traversing the magnetosheath and impinging upon the magnetopause, triggering a diverse array of geoeffects. However, the evolution of HSJs during their propagation from the bow shock to the magnetopause still remains unclear. Leveraging multi-satellite data from MMS (2015–2023), THEMIS (2008–2023), and Cluster (2001–2020), we have compiled a comprehensive data set of nearly 40,000 HSJs to statistically study the velocity evolution of HSJs from the bow shock to the magnetopause for the first time. It is shown that the occurrence rate of HSJs depends on their relative positions within the magnetosheath, peaking in the middle region. Typically, in the GSE coordinates, as HSJs penetrate into the magnetosheath, the $��V_x�$ component gradually decreases until they reach the magnetopause, where HSJs are deflected and their $��V_y�$ and $��V_z�$ components are enhanced. Meanwhile, some HSJs are redirected backwards owing to rebounce of the magnetopause, resulting in the sunward flow. Notably, the velocity-direction distribution of HSJs in the $��\left(��y�,�z��\right)�$-plane is largely isotropic overall yet exhibits a subtle dusk-favored asymmetry. This distribution aligns with the background flow throughout the evolution of HSJs, a feature that is consistent with the outcomes of 3-D global simulations. This strong consistency implies HSJ transverse velocity tends to align with the ambient magnetosheath flow even early in their evolution. Our study provides some new insights in better understanding the evolution of HSJs within the magnetosheaths of Earth and other planets.

Thermosphere Ionosphere Electrodynamics General Circulation Model was used to investigate the underlying physical processes of the thermospheric and ionospheric vortex-like structure over East Asia region in November 2003 superstorm. Horizontal neutral winds with a vortex configuration modulate the composition (O/N₂) perturbations, forming a two-dimensional vortex-like structure. Vertical winds also have a positive contribution to the final shape of this structure in the altitude distribution. The ionospheric vortex-like structure below the ionospheric peak height (hmF2) is dominated by chemical effects (O/N₂ enhancements) and neutral wind transport, while it is directly controlled by the neutral wind transport above the hmF2. Decreases in plasma density within the core region of this structure, driven by E × B drifts at all altitudes, also contribute to its formation. Analysis of the forcing terms driving the wind vortex in the middle thermosphere reveals the dominant role of pressure gradients, alongside the combined action from the Coriolis force and horizontal momentum advection. In the upper thermosphere, the ion drag becomes significant, but only partially offsets the substantial positive effects of pressure gradients. Furthermore, controlled numerical experiments demonstrate that the storm intensity is not the single trigger mechanism for this structure. Instead, the asymmetrical prevailing circulation is more beneficial to the formation of the vortex-like structure. The storm onset time also affects the formation and location of this structure, although it is more likely to appear near the magnetic poles, primarily in the American and East Asian sector.

During the 21–22 January 2005 magnetic storm, the FAST satellite observed warm (< few keV) ions in discrete energy bands on the dayside at ∼3,000 km altitude for more than 6.5 hr. We suggest that the ionospheric energy-banded ions represent the low-altitude edge of the warm plasma cloak observed simultaneously by magnetospheric satellites. This is a clear example of the multi-species ion energy bands (10 eV to several keV) observed during strong magnetic storms by the FAST satellite, stretching from the diffuse auroral region to the plasmapause with lifetimes up to 12 hr. The close association of these energy-banded ions with magnetic storms, their broad latitudinal extent, and the presence of multiple ion species in the same energy band, rather than at the same velocity, indicate that this is a distinct phenomenon from other types of energy-banded ions. During the 21–22 January 2005 magnetic storm, the dayside ion energy band structures, centered at 10 eV (H⁺), 40 eV (H⁺ and He⁺), and 160 eV (H⁺, He⁺, and O⁺), were consistent with a “time-of-flight and velocity filter” formation process acting on a near-cusp, impulsive outflow of a <200 eV multi-species ion-source population, poleward and in the same hemisphere as FAST. Understanding the sources and dynamics of warm energy-banded ions and their linkage to the warm plasma cloak is important because during superstorms these ions are transported to L values as low as L ∼ 1.2 in the dawn sector, significantly altering the energetics of the mid-latitude ionosphere.