Journal of Geophysical Research: Space Physics最新文献

This study demonstrates the feasibility of applying Physics-Informed Neural Networks (PINNs) to reconstruct the spatial and temporal evolution of two-dimensional magnetohydrodynamic (MHD) reconnection structures from limited in situ observational data. By embedding the complete set of MHD equations into the loss function, the reconstructed solutions naturally satisfy the governing physical laws. The reconstruction accuracy is systematically evaluated by varying the number, spatial distribution, and sampling interval of observation points. The analysis reveals that placing observation points both upstream and downstream of the plasmoid significantly enhances reconstruction accuracy, highlighting the importance of capturing both the early-time evolution near the $��X�$-point and the well-developed downstream structures. These findings demonstrate the potential of PINNs as a powerful tool for recovering large-scale MHD reconnection structures from sparse data, while also providing practical guidance for the design and operation of future multi-satellite observation missions.

When particles from the radiation belts impinge on the atmosphere, they can be absorbed into the atmosphere or deflected back into the magnetosphere. The deflection of particles back into the magnetosphere is known as backscatter, and it is a key link connecting the atmosphere to the magnetosphere—involving collisions with atmospheric neutrals, magnetic mirroring, the production of secondary emissions, and energy transfer from the particle to the atmosphere. Backscatter is both a feedback mechanism to magnetospheric precipitation drivers and an indirect measure of atmospheric energy absorption, making it an important process to quantify and understand. In this work, we use data from the Electron Fields and Losses INvestigation (ELFIN) satellites to quantify backscatter rates. We find that backscatter rates vary between $��\sim �5�\%�$ during periods of loss cone filling and $��\sim �90�\%�$ during periods without loss cone filling. We then compare the ELFIN backscatter data to the results of an updated and improved Monte Carlo-based simulation and find excellent agreement with ELFIN-measured backscatter rates. Finally, we use our improved Monte Carlo model to characterize the pitch angle and energy dependence of backscatter and the pitch angle distributions of backscattered electrons, finding results consistent with previous modeling efforts.

The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) onboard the FORMOSAT-2 satellite studied global Transient Luminous Events (TLEs), which occur between the troposphere and ionosphere. Using deep learning techniques, the ISUAL TLE event list from July 2004 to June 2016 was systematically constructed, containing 66,586 events. ISUAL is the satellite dedicated to TLE observation, mapping the global distribution of TLEs, and revealing distinct spatial patterns. Elves were most frequent over oceans, sprites over land, halos over coastal areas, and blue jets and gigantic jets predominantly in low-latitude regions. This study first constructed a global TLE occurrence density map through the fusion of ISUAL TLE observations and World Wide Lightning Location Network intense lightning distributions. The corrected global TLE occurrence rate is 47.08 events per minute, notably exceeding earlier studies, with individual rates of elves (32.74), sprites (5.94), halos (2.98), blue jets (5.40), and gigantic jets (0.02). Furthermore, TLE occurrence rates were examined across different climate zones using the Köppen classification system. Higher rates were found in tropical and temperate climates, with sprites particularly frequent in hot summer regions. To further examine potential external drivers, this study for the first time analyzed a full 11-year solar cycle activity in relation to nighttime TLE occurrence, revealing only a weak correlation (R ≤ 0.3) and favoring meteorological factors instead of solar activity as the primary drivers of TLE variability.

Hall magnetic fields at Earth's dayside magnetopause provide key diagnostics for collisionless reconnection and the associated Hall-current closure. Using observations from Magnetospheric Multiscale (MMS) mission, we present a unified framework to classify out-of-plane Hall fields by peak composition—central unipolar (C), sunward bipolar (S + C), earthward bipolar (C + E), and tripolar (S + C + E) - and by their displacement relative to the magnetopause midplane. We apply this framework to seven bipolar events (H1–H7) and relate Hall-field displacement to the Hall-region density asymmetry parameter. For the first five earthward-type events (H1–H5), Hall-density asymmetry covaries with the observed displacement of the bipolar Hall field structure, indicating that asymmetric Hall-density produces a larger offset of the peak amplitude toward the magnetosphere. Previously, the sunward-type event H6 was displaced toward the magnetosheath with moderate Hall-field asymmetry. On 16 October 2015 (H7), we find a sunward bipolar (S + C) signature but displaced deep into the magnetosphere, reaching a nearly symmetric Hall-field ratio despite high Hall-density asymmetry. In H7, the absence of a magnetospheric E peak, together with the complete traversal of the Hall-region into the magnetosphere, rules out a tripolar configuration previously proposed for H6. In addition, sequential electron jets and a new pattern in the bipolar normal electric field coincide with the magnetospheric Hall interval in H7. This suggests that displaced Hall electron dynamics, together with extreme asymptotic density and high temperature asymmetry, reshaped the bipolar Hall magnetic field. The findings of this study provide observational constraints for kinetic Hall models of asymmetric guide-field reconnection.

The plasmaspheric hiss and plasmatrough exohiss represent typical whistler-mode waves found within the Earth's inner magnetosphere, playing a vital role in the dynamic alterations of the Van Allen radiation belts. Under specific conditions, plasmaspheric hiss waves can escape from the plasmapause and develop into exohiss waves. In this study, it was found that in some cases, exohiss exhibits an upper and lower band structure within the frequency range from 20 Hz to several kHz. Utilizing data collected by the Van Allen Probe A between 2012 and 2019, we successfully identified double-band plasmaspheric hiss and double-band plasmatrough exohiss. Based on these statistical results, we analyzed the amplitude (Bw) distribution of double-band hiss and exohiss waves across various magnetic local times and L-shells (L), as well as different magnetic latitudes. The results indicate that the amplitudes of both upper and lower bands of hiss waves are significantly stronger than those of upper and lower bands of exohiss waves. Further integration of the analysis of the Poynting vector and ray tracing simulation suggests that both upper and lower bands of exohiss waves may be derived from double-band hiss waves inside the plasmapause. In addition, upper band seems to be damped more rapidly, which may experience severer Landau damping. Our findings about the source mechanisms of double-band exohiss waves further improve our understanding of the distribution and formation of whistler waves in the magnetosphere.

Combining meteor radar observations at Mohe (MH; 53.5°N, 122.5°E), Wuhan (WH; 30.5°N, 114.4°E), and Ledong (LD; 18.5°N, 108.8°E) stations and reanalysis data, we studied planetary wave (PW) activities from the troposphere to the mesosphere and lower thermosphere (MLT) during the major 2018/2019 sudden stratospheric warming (SSW). The quasi 4-day wave (Q4DW), quasi 6-day wave (Q6DW), and quasi 16-day wave (Q16DW) were all enhanced; however, the Q4DW is the smallest increase in zonal and meridional wind amplitude. The maximum amplitudes of the Q16DW and Q6DW reached about 34.3 m/s at 55.4 km and 23.3 m/s at 53.6 km at MH, respectively. Overall, significant Q16DW and Q6DW were observed in the high-latitude stratosphere and MLT region. However, at LD, they were only evident in the MLT region. In general, the amplitude peaks decreased sequentially from the MH to WH and LD stations. More interestingly, the peak amplitudes at lower latitudes occurred behind those at higher latitudes, suggesting that these planetary waves propagated equatorward and upward. This suggests that during the SSW, strong PW activity affects not only the vertical coupling but also the dynamics at the low latitudes in the MLT region, resulting in atmospheric coupling across different latitudes. The E-P flux and zonal wave drag analyses confirmed that numerous planetary waves propagated upward and equatorward above ∼30 km. The stationary planetary wave (SPW) exerted significantly stronger drag than the Q16DW and Q6DW, indicating that SPW played a crucial role in the reversal of the zonal wind and the formation of the 2018/2019 SSW.

Atmospheric Gravity Waves (AGWs) play a crucial role in atmosphere-ionosphere coupling. Tropical cyclones (TCs) are considered one of the potential sources of AGWs. This study investigates four extreme category tropical cyclones from the last two decades over the Indian subcontinent: VSCS Phailin (2013), ESCS Fani (2019), SuCS Amphan (2020) over the Bay of Bengal, and ESCS Tauktae (2021) in the Arabian Sea. The meteorological observations confirmed the presence of deep convective activity during these TCs, which reached higher tropospheric altitudes during the TC's duration. The low cloud-top temperatures exhibited a positive correlation with the increasing lightning activity. Further, a notable increase in lightning activity was found during the intensification phases of the storm, particularly within the wind-field regions in all four cases, which could have led to an intensification of TCs. Simultaneously, an enhancement in AGW activity occurred in the mesosphere-lower thermosphere (MLT) region. Possibly, mesoscale convective system associated with the TC led to the formation of AGWs that propagated in both the vertical and horizontal domains to higher altitudes in the MLT region. The propagation of vertical and horizontal AGWs induced by TCs at higher altitudes has been validated and quantified by analyzing vertical temperature profiles obtained from SABER and day-night band DNB imagery from VIIRS satellites. Both vertical and horizontal wavelengths of AGWs showed peak power of waves during the maximum intensity stages of TCs. Both vertical and horizontal components of AGWs are quantified for the first time over the Indian region.

The May 2024 superstorm, as the most intense geomagnetic storm since 2003, caused a variety of disturbances in the magnetosphere-ionosphere-thermosphere system. This study investigates the long-lasting electron density depletion in the polar region and the underlying ionosphere-thermosphere coupling, based on a comprehensive set of observations from ground and space. Initially, a significant amount of solar wind energy was dissipated at high latitudes, and we estimate that the hemispheric Joule heating reached 1.25 TW by using a newly developed method that utilizes SuperDARN, SuperMAG, and AMPERE data. This intense heating increased the ion temperature by 500–1,200 K in the polar region, as detected by the EISCAT Svalbard radar (ESR). Furthermore, Joule heating caused significant upwelling of the polar thermosphere, evidenced by 300%–480% increase in neutral mass density and a substantial depletion in $��\Sigma �O�/�N_2�$ up to 50%, as observed by several low-Earth-orbit satellites. Both the increase in ion temperature and the change in neutral composition are crucial factors in accelerating the F-region recombination process. Consequently, the transition altitude of molecular to oxygen ions increased dramatically from 200 to 380 km, as detected by the ESR radar. The ultimate consequence was a severe depletion in electron density in the polar F–region ionosphere, reaching 70%–85% on 11 May, which gradually recovered over the next two days. Our analysis underscores the importance of simultaneous, multi-instrument observations for a comprehensive understanding of the coupling chain during extreme geomagnetic disturbances.

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.