Journal of Geophysical Research: Space Physics最新文献

We conducted observational studies of ionospheric responses to the geomagnetic storm on 12 May 2021. We selected three cases that the electron density altitude profiles observed by Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) exhibited significant longitudinal differences in less than 30° longitudes. These cases occurred over the Atlantic Ocean and during the storm's recovery phase. All three cases show relatively weaker variations on the west side between disturbed and quiet time (<10%), while displaying pronounced positive/negative electron density variations on the east side (as large as 100%). GOLD and ICON observations illustrate that the thermospheric composition plays a minor role in the longitudinal differences, while neutral winds and disturbed electric fields make major contributions. Furthermore, significant longitudinal differences in E×B drift and neutral winds have also been observed, which will be part of the future work. This study provides unique insights into ionospheric responses within 30-degree longitude range over the ocean.

In this study, we conduct an in-depth analysis of Whole Atmosphere Community Climate Model-eXtended simulations to examine physical mechanisms of the formation and evolution of an equatorial ionization anomaly (EIA) merging phenomenon during a storm on 4 November 2021. A quantitative analysis reveals that the rapid decay of the EIA crests at their poleward sides at altitudes of ∼200–250 km plays a crucial role in the EIA merging during that day. This rapid decay is due to the fast recombination at low altitudes (∼200–250 km) as the plasma are transported downward by the westward disturbance dynamo electric field and poleward neutral winds during the storm. The results suggested EIA-merging is not merely northern and southern EIA crests moving together, but it involves a crucial rapid decay of the EIA crests at their poleward sides that descended to low altitudes (rapid recombination, ∼200–250 km), driven by regional electric fields and neutral winds. This study plays a crucial role in our understanding of the evolution and formation of the merged EIA on 4 November 2021 during the storm.

Magnetic holes (MHs) are the magnetic structures characterized by the significant decreases of magnitude field, and they have been widely observed in various space plasmas. The high-resolution observations by NASA's Magnetospheric Multiscale Mission and the Dispersion RelAtion From Timing (DRAFT) method enable us to study the wave-particle interactions in MHs in great detail. In this paper, we report whistler waves in a contracting MH and reveal their dispersion relation with DRAFT method, which is well-consistent with the theoretical prediction. During the excitation of the whistler waves, we also find the formation of pancake distribution (corresponding to electron temperature anisotropy T_⊥/T_// > 1). By calculating the growth rate of the whistler waves with an analytical model, we find such waves are generated by the temperature anisotropy (T_⊥/T_// > 1) at the center of MH, which is formed during the contraction. These results suggest that wave-particle interactions may be closely related to the large-scale evolution of the MH structures.

The long-term (2009–2019) TEC variation over a southern low latitude station Cocos Islands (12.2°S, 96.8°E) lying in edge of the Equatorial Ionization Anomaly (EIA) region and around the WN4 peak longitude are investigated and compared with its magnetic conjugate station Dibrugarh (27.5°N, 95°E). The causative mechanisms for the observed intra- and inter-seasonal variations are explored via the study of EEJ, neutral O/N₂ ratio, hmF2, meridional winds and IRI simulations. The month-to-month variation of the mean TEC showed a tendency of peaking in November (early summer) during 2009/2018 but in March (autumn) during 2014. In contrast, the seasonal maximum was always in March (spring equinox) over Dibrugarh. The hemispheric asymmetry was significant during the solar minimum period. The intra-seasonal variation of the asymmetry showed a relation to the position of the sub-solar point and solar activity. The equatorial anomaly was estimated by comparing it with equatorial TEC. The anomaly affected the stations only during respective summer of 2009/2018 whereas during 2014 the anomaly affected both stations from February to April. The monthly mean TEC over Cocos was well correlated with EEJ only during 2014. In contrast, the TEC was correlated with hmF2 in both 2009 and 2014. The IRI-2020 mostly overestimated TEC with the exception of March equinox of 2014 when the EIA effect was strongest over the stations. The dynamics of TEC variation over Cocos seemed to vary from solar minimum to maximum, changing from being photo-chemically driven to electric field driven with increase in solar activity.

In this paper, dayside magnetopause energy transport (energy transport across the separatrix surface to the magnetopause boundary layer and energy transport inside the magnetopause boundary layer) and its dependence on the magnetopause dynamic evolution under purely southward interplanetary magnetic field (IMF) conditions are studied via a 3-D global hybrid simulation. By investigating the energy transport across the separatrix surface, current layer surface, and magnetopause surface, we find that the energy transport from the magnetosheath to the magnetopause boundary layer is mainly in the form of electromagnetic energy, while the energy transport directly across the magnetopause surface to the magnetosphere is mainly in the form of plasma energy. The energy transport across the magnetopause surface exhibits temporal variability, driven by the dynamic evolution of reconnection and flux rope. During the development of multiple X-lines reconnection and flux rope, a substantial portion of solar wind energy does not directly penetrate the dayside magnetopause to the magnetosphere. Instead, it is transported with the reconnection outflow and flux rope from low latitude to high latitude, and with the drifting flow from the subsolar region to the tail magnetopause within the magnetopause current layer. These results significantly improve our understanding of solar wind-magnetosphere coupling at the dayside magnetopause.

This study investigated the day-to-day variability of ionospheric electron temperature (T_e) over Sanya using the newly built Sanya Incoherent Scatter Radar (SYISR; 18.3°N, 109.6°E, dip latitude: 12.8°N). The 24 days of observations with transmitted beams encoded by the alternating code and directed toward the zenith provided T_e profiles during April–May 2022. The spatial-temporal resolution was as precise as 4.5 km and ∼120 s. The day-to-day variability of T_e over Sanya thus revealed, which was strong in the sunrise T_e peak region (above ∼260 km, duration increases from ∼0.5 to ∼3.5 hr with altitude) and the top of the 200–300 km T_e bulge (∼260 to ∼300 km, lasting from ∼09:00 LT to ∼18:30 LT). The day-to-day variability of T_e in the two regions could reach ∼26% and ∼16% of the average T_e, respectively. Although the day-to-day variability of T_e is negatively correlated with the variation of ionospheric electron densities (N_e) in general, a positive correlation still occurred during the daytime, especially at 400–480 km from ∼17:00 LT to ∼18:00 LT. Further Thermosphere Ionosphere Electrodynamics General Circulation Model simulations reproduced the positive correlation, which may result from the internal heat exchange between electrons, ions, and neutrals. The simulations suggested that the variation of solar radiation/geomagnetic activity contributes most to the daytime/sunrise day-to-day variability of T_e over Sanya.

On 20 December 2015, three Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft detected a nightside magnetotail reconnection event in the early main phase of a major geomagnetic storm. The spacecraft (P5, P4, and P3) had their footprints located over North America near the Gillam ground magnetometer station in Canada. Multipoint observations, both in space and from the ground, allow for an examination of the spatiotemporal characteristics of the disturbance on the ground and the associated physical drivers in the magnetosphere and ionosphere. This study shows that the horizontal geomagnetic field d$��B_h�$/dt localized (on the scale of 100–300 km) feature observed at Gillam ground magnetometer site was caused by an isolated substorm onset near that station driven by a nightside magnetotail reconnection event detected by three THEMIS spacecraft that were located near the central plasma sheet. A close inspection of equivalent ionospheric current and current amplitude maps derived from ground magnetometer measurements using the spherical elementary current system technique indicates that the location of the localization lies roughly between the upward and downward field aligned current system, which is consistent with other earlier studies. This event represents the first reported observation of ground d$��B_h�$/dt localization that is directly linked to nightside magnetotail fast flow bursts and reconnection event during the onset phase of a major Geomagnetic disturbance (GMD).

We present a study of diurnal tidal variations in the mesosphere and lower thermosphere (MLT) region over Yinchuan (38.8°N, 106.8°E) during the 2020 Northern Hemisphere winter sudden stratospheric warming (SSW) event. This research utilizes data from a newly established meteor radar at Yinchuan, in conjunction with the Specified Dynamics Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (SD-WACCM-X), the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis data, and a meteor radar in Beijing, China (40.3°N, 116.2°E). Our analysis reveals a significant enhancement in the amplitude of the diurnal tide during the 2020 SSW in both meridional and zonal wind components, exceeding the climatological mean by two standard deviations. The variation in the ratio of absolute vorticity to planetary vorticity in the MLT region is known to correlate with diurnal tide amplitude. Our findings indicate that the zonal-mean zonal wind in the MLT underwent a dramatic change during the SSW, with the ratio beginning to decrease 2 days prior to the event. This suggests that changes in the zonal-mean zonal wind during the SSW may play a crucial role in the observed amplification of the diurnal tidal amplitudes. Nevertheless, further investigations are needed to better understand the amplification of diurnal tides in the MLT region during SSWs.