Journal of Geophysical Research: Space Physics最新文献

The Earth's magnetopause flanks are commonly unstable to the Kelvin-Helmholtz (K-H) instability, which is excited by the velocity shear between the magnetosphere and the magnetosheath. The K-H instability generates magnetopause surface waves, which steepen into non-linear vortices that mix plasmas from the two regions, and transport magnetosheath plasma into the magnetosphere. One of the candidate mechanisms for the plasma mixing identified in numerical simulations are finite Larmor radius (FLR) effects, which become active along the magnetopause when it is deformed by K-H waves, and steepened to a thickness comparable to the thermal particle Larmor radius. Diffusive magnetosheath plasma transport into the magnetosphere occurs when the FLR mixing region is disrupted by turbulence. In this work, we use Magnetospheric Multiscale Mission data to show in situ evidence of an ion FLR ion mixing region during magnetopause K-H wave boundary crossings under northward interplanetary magnetic field conditions. We show that these crossings contain ion heat flux enhancements that are consistent with being generated by ion FLR mixing across a temperature gradient. In accordance with kinetic transport theory and our past numerical results, these enhancements are transverse to the local magnetic field and temperature gradient. Our present findings indicate that the K-H waves produce copious FLR ion mixing, which could have an important role in the K-H driven transport of magnetosheath plasma into the magnetosphere. We also demonstrate that heat flux measurements could be used for identifying K-H waves at different evolutionary stages.

Ionospheric density variations can be inferred by studying the effects of electron density structures on transionospheric High Frequency (HF) radio wave propagation. The Radio Receiver Instrument (RRI) on the Enhanced Polar Outflow Probe (e-POP)/Swarm-E is used to detect HF radio waves during transionospheric experiments conducted between the space-based RRI and ground-based HF transmitters. A Faraday rotation rate-based method is used to convert RRI HF observations into ionospheric density variations. Two geomagnetically quiet-day periods in December 2017 are examined, where HF waves from the Ottawa transmitter reveal ionospheric structures with scale sizes from 7 to 750 km. Comparisons with GPS differential Total Electron Content (dTEC) show similar scale sizes. While RRI dTEC agrees with GPS-derived dTEC for large-scale features, RRI additionally detects small-scale fluctuations that are comparable to or surpass the magnitudes of large-scale variations. Excursions from large-scale variations observed by RRI are $��\sim �$2 TECU in narrow latitudinal bands of $��\sim �$0.25° corresponding to $��\sim �$25 km. RRI and GPS dTEC variations suggest the continuous existence of 300–350 km scale-size structures on both days. Moreover the high sampling rate of RRI enhances the measurement capability of small-scale spatial variations and indicates a quiet-time ionosphere dominated by small-scale total electron content variations. RRI measurements give insight into the scale size of localized, transient ionospheric phenomena that affect HF radio wave propagation.

This paper offers an in-depth analysis of the 10–11 May 2024 solar storm's time evolution. It integrates the European Heliospheric Forecasting Information Asset (EUHFORIA) and Gorgon-Space models to explore the effects on Earth's magnetosphere, including its state and reactions, ionospheric currents, and cross-polar cap potential (CPCP) responses to the solar wind. Observations from Super Dual Auroral Radar Network (SuperDARN) are used to validate the numerical findings. Two specific time frames on May 10 are examined: one representing quiet conditions and another with active polar cap convection cells. This allows for an assessment of how well the simulations align with the actual observations. The investigation includes a thorough look at the temporal evolution, the number of convection cells, and their spatial distribution within the polar cap and CPCP area. Additionally, the research explores the scattered patterns of convection cells, including instances of multiple cell formations. The study compares the simulated $��K_p�$ and CPCP values with observed data from ground magnetometers and SuperDARN to gauge consistency. The encouraging overall agreement suggests the numerical results could offer improvements for addressing the underestimation of CPCP in SuperDARN observations. Furthermore, the model's ability to estimate the magnetopause radius is evaluated against previous models, while temporal structures in the plasma convection maps predicted by the EUHFORIA/Gorgon-Space models are also scrutinized.

During Juno's only flyby of Europa, the Jupiter Energetic Particle Detector Instrument (JEDI) measured complex dropouts in the energetic ion flux in Europa's wake. We investigate the causes of these dropouts, focusing specifically on energetic protons of $��\sim �100�$ keV and $��\sim �1�$ MeV, using back-tracking particle simulations, a prescribed description of Europa's atmosphere and a three-dimensional single fluid magnetohydrodynamics (MHD) model of the plasma-atmosphere interaction. We investigate the role of magnetic field perturbations resulting from the interaction between Jupiter's magnetospheric plasma and Europa's atmosphere and the presence of field-aligned electron beams in Europa's wake. We compare the simulated effect of the perturbed fields on the pitch angle distributions of the ion losses to Juno-JEDI measurements. We find that at $��\sim �100�$ keV, field perturbations are the dominant factor controlling the distribution of the losses along the flyby, while at $��\sim �1�$ MeV a combination of field perturbations and absorption by the surface due to short half bounce periods is required to explain the measured losses. We also find that the effect of charge-exchange with Europa's tenuous atmosphere is weak and absorption by dust in Europa's environment is negligible. Furthermore, we find that the perturbed magnetic fields which best represent the measurements are those that account for the plasma interaction with a sub-/anti-Jovian asymmetric atmosphere, non-uniform ionization of the atmosphere, and electron beams. This sensitivity to the specific field perturbation demonstrates that combining observations and modeling of proton depletions constitute an important tool to probe the electromagnetic field and atmospheric configurations of Europa.

Microinjection phenomena, characterized by short-periodic and energy-dispersed enhancements of electron flux, are frequently observed in the Earth's outer magnetosphere. Their generation mechanism remains debated. Recently, the drift resonance between ultra-low frequency (ULF) waves and energetic electrons was proposed as a key candidate mechanism distinct from conventional injection-driven processes. In this study, we investigate this new generation mechanism of microinjection phenomena through theoretical extension, case analysis, and statistical evaluation. We extend classical poloidal mode drift resonance theory to include arbitrary equatorial pitch angles, enabling broader applicability. A representative microinjection event exhibiting poloidal mode drift resonance characteristics was analyzed in detail. Based on MMS observations in 2016, we analyze 153 microinjection events and found a strong frequency correlation with ULF waves and a predominant dusk-side occurrence. These results provide robust evidence that drift resonance is a fundamental and widespread mechanism responsible for microinjection phenomena in the magnetosphere.

This study investigates the characteristics of medium scale traveling ionospheric disturbances (MSTIDs) relative amplitudes ($��\delta �N�e�/�N�e�$) in the ionospheric E to lower F regions, using the EISCAT VHF radar data measured from 41 daytime runs in years 2008–2024 carried out mostly between $��7�-�13�$ UT. Spectral analysis is applied to identify the dominant wave amplitudes and periods, while a cross-correlation method is used to determine the vertical wavelength, $��{\lambda }_z�$. It is observed that the dominant $��\delta �N�e�/�N�e�$ reveal both seasonal and height variations. The amplitudes of MSTIDs observed during winter ($��6�-�13�\%�$) are approximately $��5�-�10�$ times larger compared to other seasons (2.5$��\%�$

A unique rippling luminous structure near the main aurora, lacking a red glow and smaller in scale, has been documented. These ripples are not caused by electron or ion precipitation along geomagnetic field lines. We have characterized these Fragmented Aurora-like Emissions (FAEs) through statistical analysis, revealing that they appear as green, periodic structures near the poleward edge of a strong aurora arc, especially when the arc retreats from higher latitudes. Moreover, FAEs tend to appear earlier when the aurora arc retreats more rapidly from its maximum expansion. The distances between the ripples range from 4 to 5 km. We present new evidence supporting the hypothesis that FAEs are caused by plasma gradient drift instability ripples occurring near the aurora ionosphere. This research expands our understanding of aurora dynamics and the physical processes in aurora regions; FAEs can be regarded as a signal of the environment around aurora reach to the gradient drift instability favorable conditions.

This study re-examines ionospheric responses to the Mw 9.1 Tohoku-Oki earthquake of 11 March 2011, using data from nearly 1200 GEONET GPS receivers distributed across Japan. The focus is on co-seismic ionospheric perturbations (CIP) induced by Rayleigh surface waves, referred to here as Rayleigh wave-generated co-seismic ionospheric perturbations (RAW-CIP). Significant RAW-CIP signatures were observed in Total Electron Content (TEC) time series from multiple GPS satellites. From the spatiotemporal evolution of these perturbations, their propagation velocities and amplitude variations were estimated. Concurrently, seismic data from 64 broadband stations across Japan were analyzed to derive period-dependent group velocities using dispersion curve analysis and amplitudes of Rayleigh surface waves. A comparative assessment revealed that Rayleigh waves with periods between 10 and 50 s were most effective in coupling with the ionosphere. The average propagation velocities of these surface waves showed good agreement with those of RAW-CIP, and their amplitude variations also correlated well. These findings highlight that low-frequency Rayleigh surface waves can be reliably characterized using ionospheric observations, as they effectively manifest in the ionosphere.

Solar wind–magnetosphere interaction is a major driver of global plasma convection in planetary magnetospheres. In Earth's magnetosphere, this convection is governed by magnetic reconnection on the dayside and nightside. Dayside reconnection alone can rapidly re-establish convection within closed field lines, typically within 10–20 min following a southward turning of the interplanetary magnetic field (IMF). In this study, we show that solar wind speed strongly regulates the evolution and structure of this convection. Using global magnetohydrodynamic (MHD) simulations under the condition, we compare the magnetospheric response to southward IMF turnings under fast (800 km/s) and slow (400 km/s) solar wind streams. In the fast stream case, enhanced convection extends from the dayside magnetopause to 20 $��R_E�$ down the magnetotail within 15 min, compared to approximately 20 min in the slow stream case. The fast stream also drives deeper and more intense convection, accompanied by stronger Region 1 field-aligned currents (FACs) and enhanced flow shear in the low-latitude boundary layer. In both fast and slow wind cases, the induced convection exhibits discrete spatial and temporal channels. These results demonstrate that solar wind speed is a key parameter controlling the development of induced magnetosphere convection, with important implications for global solar wind–magnetosphere coupling.