Journal of Geophysical Research: Space Physics最新文献

We present multi-platform observations of plasma cloak, O+ outflows, kinetic Alfven waves (KAWs), and auroral oval for the geomagnetic storm on 17 March 2015. During the storm's main phase, we observed a generally symmetric equatorward motion of the auroral oval in both hemispheres, corresponding to the plasmasphere erosion and inward motion of the plasma sheet. Consequently, Van Allen Probes became immersed within the plasma sheet for extended hours and repeatedly observed correlated KAWs and O+ outflows. The KAWs contain adequate energy flux toward the ionosphere to energize the observed outflow ions. Adiabatic particle tracing suggests that the O+ outflows are directly from the nightside auroral oval and that the energization is through a quasi-static potential drop. The O+ outflows from the nightside auroral oval were adequate ($��1�0^8�$-$��1�0^9�$ #/$��{�c�m�}^2�$-s) and prompt (several minutes) to explain the newly formed plasma cloak, suggesting that they were a dominant initial source of plasma cloak during this storm.

The present study performs a procedure of estimating the current sheet (CS) thickness in the solar wind. Motivated by the science requirements for a multi-spacecraft solar wind mission called the Seven Sisters, this research aims to address the required temporal resolution of the magnetometer in order to entirely encompass the observations of thin CSs. Additionally, this procedure can contribute to addressing the unresolved turbulence heating problem in the solar wind. We have statistically provided the solar wind CS thickness estimated, with full instrumental resolution of 128 Hz, from the Flux Gate magnetometer (FGM) data of the Magnetospheric Multiscale (MMS) mission. Out of 183 cases of solar wind CS crossings, the thicknesses varied from 0.1 to 3 Mm with a maximum of 32.97 s, minimum of 0.16 s and average of 3.08 s crossing time. Of these, 73.22% of the CSs can be identified by using 1-Hz measurement cadence, while 12.5 Hz data can fully identify all of the CSs. Therefore, it can be concluded that the 1-Hz sampling rate is sufficient for the survey mode, while the sampling frequency of 12.5 Hz as the burst mode is capable of achieving even the strictest scientific objectives. Our statistical results also report a population below 100 km or $��1�d_i�$, which should be further examined.

The prereversal enhancement (PRE) is a brief surge in upward plasma velocity in the evening equatorial ionosphere and a driver of equatorial spread-F. This study reports the first PRE climatology from Ionospheric Connection Explorer (ICON) data, exhibiting seasonal and longitudinal variability that is qualitatively consistent with results from two previous satellite missions. Previous missions, however, lacked the neutral wind observations to characterize their impact on the PRE. To quantitatively assess wind impacts, numerical experiments are performed with a standalone dynamo solver using winds from the TIEGCM-ICON, which is driven from below by observed tides. To quantify the impact of solar/magnetic geometry, such as the alignment between the solar terminator and the magnetic meridian, the model was first driven with seasonally and longitudinally averaged winds (which includes seasonally averaged zonal-mean winds and migrating tides). This reproduces the observed PRE variability with a correlation of 0.44. Incorporating longitudinally and seasonally varying wind patterns improves the correlation to 0.68. This suggests that climatological wind variability is an important driver of PRE variability, but future work is needed to account for the missing variability. Potential missing drivers include conductivity variability near the terminator and mesoscale wind features such as the solar terminator wave.

Based on the entire dataset collected by the Cassini Plasma Spectrometer, we provide a comprehensive picture of the pitch angle (PA) and velocity distributions of pick-up ions (PUIs) in Saturn's inner and middle magnetosphere. We investigate the dependence of these distributions on Saturnian Local Time and magnetic latitude. We also search for correlations with the signatures of ion cyclotron waves (ICWs) observed by the Cassini magnetometer. Our survey reveals that ion PA distributions have a pancake shape and their full width increases monotonically with magnetic latitude. This increase in angular width is anti-correlated with the observed amplitudes of ICWs that are generated during the thermalization of the PUI distribution. We find no evidence of the previously observed, non-monotonic change of wave amplitudes with magnetic latitude mapping into the width of the PA distributions. This suggests that only a small fraction of the energy deposited into the waves is transferred back to the ions to broaden the distribution. We find that the PA scattering time is several times the bounce period, meaning PUIs become PA scattered only after completing several cycles of bounce motion and, hence migrating to higher latitudes by the time they become more isotropic. When moving away from Saturn's magnetic equatorial plane, the observed half-width of the velocity distributions does not evolve appreciably with latitude and $��L�$ shell value. This behavior changes only outside the orbit of Rhea where the observed velocity distributions begin to broaden due to elevated plasma temperatures.

The equatorial ionization anomaly (EIA) is the salient feature of the low-latitude ionosphere, characterized by two crests around magnetic latitudes ±15° and one trough around the dip equator. The effects of the subauroral polarization streams (SAPS) on EIA are rarely studied, impairing our understanding of high- and low-latitude ionospheric coupling during geomagnetic storms. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) with an empirical SAPS model and GPS observed total electron content (TEC) to identify the SAPS effects on the EIA during the geomagnetic storm on 17 March 2015. Our results show that the low-latitude TEC (∼±20° magnetic latitudes and 12–16 LT) is enhanced by 5 TECU (∼5%) due to SAPS effects. This enhancement is found at both the crests and trough of EIA. A term-by-term analysis of the ion continuity equation is performed in TIEGCM. The SAPS-induced equatorward winds (∼30 m/s) are the most important in producing electron density enhancement at the topside ionosphere. The ionosphere is lifted to higher altitudes where the chemical recombination is slower, causing the TEC and electron density enhancement. However, at the bottomside F-layer ionosphere, the electron density enhancement is dominated by the downward E × B drifts (∼5 m/s) driven by SAPS.

We explore the three-dimensional structure of ion-kinetic instabilities in a thin current layer using a hybrid-Vlasov simulation of the Earth's magnetosphere. The simulation shows the simultaneous growth of tearing and kinking instabilities, which develop in the Sun-Earth and dawn-dusk directions, respectively, within the magnetotail current sheet. The formation of flux ropes indicates the development of the tearing instability, while flapping-type cross-tail oscillations arise from the kink instability. We consider both instabilities as independent polarizations, albeit sharing a common source: demagnetized ions forming crescent-shape distributions at the center of the current layer. These oscillations exhibit spatiotemporal characteristics within the proton-scale range, featuring a growth time on the order of 40–80 proton gyroperiods and a wavelength of approximately 15–30 proton skin depths.

New basis functions, suitable for fitting magnetic field observations of the auroral and equatorial electrojets, are constructed by applying principal components analysis (PCA) to a set of rotated current loops in the ionospheric E-layer. The current loops, which are defined with respect to quasi-dipole coordinates, are placed in the electrojet regions (northern polar, equatorial, and southern polar) and are then rotated and tilted to capture both zonal and meridional flow directions, enabling a fully 2D representation of the toroidal flow in the E-layer. We consider four possible covariance functions that define correlation between individual loops, and use PCA to derive a set of modes representing toroidal electrojet current flow. These modes can be fitted to magnetic field observations recorded in space and/or on ground in order to reconstruct an equivalent height-integrated current system in the E-layer which best describes the measurements. We present an application of this new technique, which we call LoopPCA, to model quasi-steady ionospheric current systems, by fitting mean ionospheric magnetic fields recorded by the Swarm satellite mission over a 6 year time period.

Limited by the number and location distribution of ground stations, the ground based ionospheric detection using Global Navigation Satellite Systems (GNSS) technology suffers from low accuracy and poor reliability in some regions. To improve the performance of the global ionospheric model, this study combines the Continuously Operating Reference Station and the Low Earth Orbit (LEO) Satellite observation to conduct the ground and space-based (G/SBased) joint ionospheric detection technique. With reference to the ionospheric radar data of the global ionospheric radio observatory, the performance of the G/SBased GNSS joint ionospheric detection technique was tested in quiet and disturbed geomagnetic environments. Results show that in the ground and space based joint mode, the distribution of ionospheric puncture points (IPPs) is uniform, thus effectively avoiding the problem of IPPs blank in the absence of ground stations. In the quiet geomagnetic environment, the ionospheric detection of the G/SBased joint mode has a remarkable performance improvement compared with the ground GNSS mode, with an average improvement of 55.51%. In the geomagnetically disturbed environment, the G/SBased joint mode still has high consistency with the ionospheric radar results, and the detection performance is better than that of the ground GNSS mode. This research shows that combining with ground GNSS and LEO satellite observation data can substantially provide the performance of GNSS ionospheric total electron content detection and can provide good data support for the construction of a global ionospheric refinement model.

On 10–14 May 2024, one of the most powerful geomagnetic storms occurred, with the Dst less than −400 nT. Quasi-periodic nighttime traveling ionospheric disturbances (TIDs) observed during the recovery phase on 13 May are explored using the detrended total electron content (dTEC) and the neutral wind measurements from Fabry-Perot interferometers (FPI) at Millstone station. At middle latitudes, the strong westward plasma drifts drove an obvious nighttime ionospheric trough at 52° magnetic latitude. Equatorward of this middle-latitude trough, quasi-periodic TIDs in dTEC were found, with a period of 1 hr and phase speeds ranging from 305.6 to 649.3 m/s. Based on the AE index, the periodic energy deposition during substorms might be responsible for the quasi-periodic oscillations of TIDs. Fortunately, FPI-measured horizontal winds at Millstone showed a quasi-periodic oscillation as well, indicating their potential key role.