Journal of Geophysical Research: Space Physics最新文献

We present observations from the Van Allen Probes of lower band chorus waves interacting with wavelength-scale density irregularities and gradients on the order of a few kilometers—comparable to the wavelength of the chorus waves themselves. High-resolution electron density is derived from the upper hybrid resonance line in the High-Frequency Receiver (HFR) merged spectrum, with a time resolution of 0.5 s. These observations show that density fluctuations modulate both the amplitude and wave normal angles of lower band chorus. High-amplitude, quasi-parallel waves are associated with regions of enhanced density, whereas very oblique waves with lower amplitude are found in regions of density depletion. The very oblique chorus waves are not generated locally by anisotropic electrons or shaped solely by propagation effects. One-dimensional wave field calculations in a multilayered plasma demonstrate that wavelength-scale density irregularities can scatter incident quasi-parallel waves and produce very oblique waves at density depletions.

We present observations from the Van Allen Probes of lower band chorus waves interacting with wavelength-scale density irregularities and gradients on the order of a few kilometers—comparable to the wavelength of the chorus waves themselves. High-resolution electron density is derived from the upper hybrid resonance line in the High-Frequency Receiver (HFR) merged spectrum, with a time resolution of 0.5 s. These observations show that density fluctuations modulate both the amplitude and wave normal angles of lower band chorus. High-amplitude, quasi-parallel waves are associated with regions of enhanced density, whereas very oblique waves with lower amplitude are found in regions of density depletion. The very oblique chorus waves are not generated locally by anisotropic electrons or shaped solely by propagation effects. One-dimensional wave field calculations in a multilayered plasma demonstrate that wavelength-scale density irregularities can scatter incident quasi-parallel waves and produce very oblique waves at density depletions.

We present a methodology for deriving the horizontal two-dimensional distribution of low-energy electron precipitation, specifically the possible lower bound of the differential energy flux of electron precipitation at 100 eV, from a 630-nm auroral image obtained with a ground-based all-sky imager. The electron energy flux required to reproduce the auroral intensity distribution can be obtained using the GLobal airglOW (GLOW) model for the magnetic field lines within the field of view of the imager. The distribution of the electron precipitation occurring in a roughly circular region with a diameter of approximately 1,400 km centered on the observation point can be determined every 10 s or so. This methodology is implemented using the data obtained during the early recovery phase of a substorm from an imager operating in Longyearbyen, Norway. A characteristic spatio-temporal variation of the electron precipitation in the polar cap boundary near midnight is revealed; the region of enhanced differential energy flux repeatedly expanded during the 20-min interval, reaching nearly 30,000 km² on three occasions when evaluated at an altitude of 250 km.

Topside plasma troughs in the mid-latitude ionosphere, accompanied by enhancements in electron temperature and the occurrence of subauroral red arcs, were observed by the Swarm-B satellite and co-located airglow measurements. To investigate the underlying physical processes, we developed a two-dimensional numerical simulation model incorporating a non-equilibrium energy equation, with particular emphasis on the roles of topside electron heat conduction and the resulting ambipolar diffusion. The key observational features of both plasma density and electron temperature were successfully reproduced by assuming a Gaussian-shaped topside heat flux. Simulation results indicate that the observed plasma trough along the Swarm-B orbit is likely driven by a transient enhancement of plasmaspheric heat flux. Additionally, the influences of meridional winds and ion composition on the asymmetry of the trough were found to be negligible. These findings underscore the critical role of plasmaspheric energy input in modulating ionospheric structures, identifying variations in electron heat flux as the primary driver. This study advances the understanding of mid-latitude trough dynamics by linking magnetospheric energy transport processes to ionospheric plasma depletion, with important implications for space weather modeling and forecasting.

Topside plasma troughs in the mid-latitude ionosphere, accompanied by enhancements in electron temperature and the occurrence of subauroral red arcs, were observed by the Swarm-B satellite and co-located airglow measurements. To investigate the underlying physical processes, we developed a two-dimensional numerical simulation model incorporating a non-equilibrium energy equation, with particular emphasis on the roles of topside electron heat conduction and the resulting ambipolar diffusion. The key observational features of both plasma density and electron temperature were successfully reproduced by assuming a Gaussian-shaped topside heat flux. Simulation results indicate that the observed plasma trough along the Swarm-B orbit is likely driven by a transient enhancement of plasmaspheric heat flux. Additionally, the influences of meridional winds and ion composition on the asymmetry of the trough were found to be negligible. These findings underscore the critical role of plasmaspheric energy input in modulating ionospheric structures, identifying variations in electron heat flux as the primary driver. This study advances the understanding of mid-latitude trough dynamics by linking magnetospheric energy transport processes to ionospheric plasma depletion, with important implications for space weather modeling and forecasting.

By combining 6-year Van Allen Probes data and 19-year US Global Positioning System (GPS) satellite NS41 observations, covering the maximum and declining phases of both Solar Cycles 23 and 24, we comprehensively investigate the statistical distributions of the storm-time maximum fluxes (j_max) of outer belt electrons and their critical controlling geomagnetic and solar wind conditions. We find that electron fluxes with energies ∼0.5–2 MeV at L = 4.2–4.5 are closely modulated by the time-integrated AL index (Int(AL)), having strong correlation coefficients (CC > 0.7) between 6-hr averaged electron fluxes and Int(AL) calculated with a sliding time window. The consistent observations of j_max from Radiation Belt Storm Probes and NS41 confirm the controlling influence of continuous substorms as measured by Int(AL) on producing j_max, showing strong and linear correlation between them in logarithmic space, even when applied to storms with (SYM-H)_min < −300 nT. Meanwhile, the combination of low solar wind pressure, large and sustained substorms and solar wind electric field are important predictors for efficient electron acceleration.

By combining 6-year Van Allen Probes data and 19-year US Global Positioning System (GPS) satellite NS41 observations, covering the maximum and declining phases of both Solar Cycles 23 and 24, we comprehensively investigate the statistical distributions of the storm-time maximum fluxes (j_max) of outer belt electrons and their critical controlling geomagnetic and solar wind conditions. We find that electron fluxes with energies ∼0.5–2 MeV at L = 4.2–4.5 are closely modulated by the time-integrated AL index (Int(AL)), having strong correlation coefficients (CC > 0.7) between 6-hr averaged electron fluxes and Int(AL) calculated with a sliding time window. The consistent observations of j_max from Radiation Belt Storm Probes and NS41 confirm the controlling influence of continuous substorms as measured by Int(AL) on producing j_max, showing strong and linear correlation between them in logarithmic space, even when applied to storms with (SYM-H)_min < −300 nT. Meanwhile, the combination of low solar wind pressure, large and sustained substorms and solar wind electric field are important predictors for efficient electron acceleration.

Collisions between ions and neutral atoms or molecules regulate the electrical conductivity in Earth's ionosphere and therefore play an important role in closing the magnetospheric current system. Here, we present measurements of the total collision cross-sections of $��A�r^{+}�$ and $��N^{+}�$ ions in the energy range from 1 to 7 keV, scattered from mixtures of different species of neutrals ($��A�r�$, $��N_2�$ and $��O_2�$). Cross sections for $��A�r^{+}�$ on the individual target species are well known and were used to validate the experimental process that was then used to measure the cross sections in mixtures of the target species. The measurements were conducted in the Space and Beam Experimental Device (SABER), which includes an ion gun to accelerate selected ion species and a movable Faraday cup that enables two different methods to measure the total cross section. The total scattering cross section of a gas mixture is commonly approximated as a weighted sum of the cross sections of the individual species, based on their respective concentrations. However, our findings indicate that the total scattering cross-section for target gas mixtures is not always equal to the proportional sum of the individual cross-sections of the mixture components.

Interplanetary shocks compress the magnetosphere and launch fast-mode waves propagating in the inner magnetosphere, which can excite field line resonance in the ultra-low frequency (ULF) range. The resulting phase delay due to wave propagation between two observation points manifests observationally as a phase difference, which is commonly used to calculate the azimuthal wavenumber. In this paper, we suggest this wavenumber to be named as effective azimuthal mode number (m*) to distinguish it from the azimuthal mode number derived from solving the MHD wave equation in a dipole magnetic field, which is ∼0 for the toroidal component and infinite for the poloidal component. Utilizing magnetic field measurements from Geostationary Operational Environmental Satellites after interplanetary shocks spanning from January 2011 to March 2024, we perform a statistical analysis of shock-induced ULF wave characteristics based on cross-wavelet analysis. Our results for dayside events reveal that the magnitude of m*-values derived from observations, denoted as $��m_{�s�c�}^{\ast }�$, for compressional, poloidal and toroidal components are predominantly less than 3. All three wave components are characterized by anti-sunward propagation. The $��m_{�s�c�}^{\ast }�$-values for the two transverse components are slightly higher than that for the compressional component. These signatures are consistent with the theory proposed in this study, providing a generalized estimation of the m*-value of shock-induced ULF waves for the analysis of radial diffusion coefficients in the radiation belts.