Journal of Geophysical Research: Space Physics最新文献

A moderate geomagnetic storm was driven by high-speed solar wind stream on 14 March 2016. We show that large-scale traveling ionospheric disturbances (LSTIDs) played a significant role in producing the ionospheric storm positive phase at mid-latitudes in the North American sector. The equatorward expansion of the positive storm phase followed the equatorward propagation of the LSTIDs, after which the total electron content (TEC) increased by 11 TECU (42%). Our novel method to estimate Joule heating suggests that sudden increases in Joule heating in the auroral oval triggered the LSTIDs. The effects of the LSTIDs observed by the Millstone Hill radar were sudden uplifts of the ionospheric F region followed by downlifts. The absence of an eastward electric field in the radar measurements rules out the role of electric field in causing the positive storm phase. We suggest that the uplifts of the ionosphere were associated with equatorward neutral wind perturbations carried along with the LSTIDs, whereas the downlifts were associated with poleward winds. During the whole period of the two LSTIDs, the TEC continued to increase. The increase in TEC during the uplift can be explained by the decrease in the recombination rate at higher altitudes under continuous solar photoionization. The maximum in peak-F density during the second downlift can be explained by compression of the plasma. To explain the increase in TEC during the downlift, an additional mechanism is needed, which could be downward plasma flux from the plasmasphere or increase in atomic oxygen due to changes in thermospheric circulation.

A moderate geomagnetic storm was driven by high-speed solar wind stream on 14 March 2016. We show that large-scale traveling ionospheric disturbances (LSTIDs) played a significant role in producing the ionospheric storm positive phase at mid-latitudes in the North American sector. The equatorward expansion of the positive storm phase followed the equatorward propagation of the LSTIDs, after which the total electron content (TEC) increased by 11 TECU (42%). Our novel method to estimate Joule heating suggests that sudden increases in Joule heating in the auroral oval triggered the LSTIDs. The effects of the LSTIDs observed by the Millstone Hill radar were sudden uplifts of the ionospheric F region followed by downlifts. The absence of an eastward electric field in the radar measurements rules out the role of electric field in causing the positive storm phase. We suggest that the uplifts of the ionosphere were associated with equatorward neutral wind perturbations carried along with the LSTIDs, whereas the downlifts were associated with poleward winds. During the whole period of the two LSTIDs, the TEC continued to increase. The increase in TEC during the uplift can be explained by the decrease in the recombination rate at higher altitudes under continuous solar photoionization. The maximum in peak-F density during the second downlift can be explained by compression of the plasma. To explain the increase in TEC during the downlift, an additional mechanism is needed, which could be downward plasma flux from the plasmasphere or increase in atomic oxygen due to changes in thermospheric circulation.

The Scale-Invariant Feature Transform (SIFT) algorithm detects key points and generates descriptors in images, enabling features matching across different images for object recognition and tracking. We derived the zonal drift velocities of equatorial plasma bubbles (EPBs) by tracking SIFT key points in GOLD Nmax data. Zonal drift velocities varied from ∼40 m/s to ∼160 m/s and exhibited prominent seasonal variations: the average drift velocity for different longitudes peaks around the Northern Hemisphere's winter solstice month and reaches its minimum near the summer solstice month. The results show that the zonal drift speeds of EPBs are larger during high solar activity, while intense geomagnetic activity suppresses eastward drift velocities. This study represents the first application of the SIFT algorithm to satellite airglow images. Our findings reveal climatological variations in ionospheric zonal drifts, providing new observational foundations for advancing the understanding of ionospheric electrodynamic processes.

During a special MMS Turbulence campaign, almost 80 min of continuous high resolution burst measurements were downlinked from a traversal across Earth's magnetosheath behind mixed quasi-parallel/perpendicular bow shock conditions. Throughout the magnetosheath, we observed magnetic holes containing intense whistler waves known as “Lion Roars” (LRs). We compared the observed properties of LRs to determine why the whistler waves included higher order harmonics in some magnetic holes but not in others. We refer to the LR events with and without harmonics as “Higher Order Harmonic LRs (HOHLRs)” and “nonharmonic LRs”, respectively. From our observations of the LR events, we found that each wave train featured an electron beam moving at the electron Alfvén speed and parallel to the background magnetic field. We also observed that this electron beam had a stronger phase space density for the LRs near the bow shock. For the HOHLR events, we observed that they exhibited a strong antiparallel Poynting flux and high counts of solitary waves surrounding their corresponding magnetic holes, with some detected solitary waves at the edges of the magnetic hole. Additionally, the fundamental frequencies for the HOHLRs were observed around 0.18–0.23 of the electron cyclotron frequency, $��f_{�c�E�}�$. For the nonharmonic LR events, we observed a strong presence of solitary waves within the confines of their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong $��\delta �E_{\parallel }�$ fluctuations, and Poynting flux flowing in an oblique direction with respect to the background magnetic field. Additionally, the fundamental frequencies of nonharmonic LRs were lower, ranging from 0.11 to 0.18 $��f_{�c�E�}�$.

During a special MMS Turbulence campaign, almost 80 min of continuous high resolution burst measurements were downlinked from a traversal across Earth's magnetosheath behind mixed quasi-parallel/perpendicular bow shock conditions. Throughout the magnetosheath, we observed magnetic holes containing intense whistler waves known as “Lion Roars” (LRs). We compared the observed properties of LRs to determine why the whistler waves included higher order harmonics in some magnetic holes but not in others. We refer to the LR events with and without harmonics as “Higher Order Harmonic LRs (HOHLRs)” and “nonharmonic LRs”, respectively. From our observations of the LR events, we found that each wave train featured an electron beam moving at the electron Alfvén speed and parallel to the background magnetic field. We also observed that this electron beam had a stronger phase space density for the LRs near the bow shock. For the HOHLR events, we observed that they exhibited a strong antiparallel Poynting flux and high counts of solitary waves surrounding their corresponding magnetic holes, with some detected solitary waves at the edges of the magnetic hole. Additionally, the fundamental frequencies for the HOHLRs were observed around 0.18–0.23 of the electron cyclotron frequency, $��f_{�c�E�}�$. For the nonharmonic LR events, we observed a strong presence of solitary waves within the confines of their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong $��\delta �E_{\parallel }�$ fluctuations, and Poynting flux flowing in an oblique direction with respect to the background magnetic field. Additionally, the fundamental frequencies of nonharmonic LRs were lower, ranging from 0.11 to 0.18 $��f_{�c�E�}�$.

The generation of traveling ionospheric disturbances (TIDs) near solar terminators has been predicted, and several studies have reported the detection of TIDs associated with sunrise. However, there are also observations that do not show TID signatures at sunrise. We address this issue by investigating false TID detection at sunrise using total electron content (TEC) data from the global navigation satellite system (GNSS) network over the United States and plasma density measurements from the first Republic of China satellite (ROCSAT-1). The TEC morphology near sunrise, characterized by a rapid TEC increase, creates significant deviations between observed and trend (or filtered) TEC values. The collective pattern of this difference (dTEC) appears as a negative dTEC band aligned with sunrise. While this feature can be interpreted as a signature of large-scale TIDs (LSTIDs), it may also falsely suggest a high occurrence rate of medium-scale TIDs (MSTIDs) when dTEC is used as a detection proxy. However, the negative dTEC band at sunrise is not indicative of LSTIDs because the rapid TEC transition at sunrise is caused by photoionization. This interpretation is supported by the detection of a similar dTEC band at sunrise in model outputs that contain no TID information. Furthermore, the distribution of electron density irregularities derived from ROCSAT-1 showed no evidence of enhanced MSTID activity near sunrise. Therefore, false TID detections near sunrise in GNSS TEC data should not be overlooked.

Earth's outer radiation belt electron flux is highly variable and can be enhanced by over an order of magnitude over timescales less than one day, as observed during the October 2012 storm. Previous studies of this storm (e.g., Reeves et al., 2013, https://doi.org/10.1126/science.1237743) have invoked local acceleration to explain this. However, here, we argue that the observations can instead be explained by fast inward radial transport. One method often invoked to distinguish between these two acceleration processes is the existence of local peaks in electron phase space density (PSD) as a function of L* at fixed first, M, and second, K, adiabatic invariants. However, this method relies on the assumption that the evolution of the PSD as a function of L* occurs over timescales slower than the satellite orbital period. Here, high spatiotemporal resolution data from the Global Positioning System (GPS) spacecraft constellation is used to show that enhancements in the PSD occur during the October 2012 storm over short timescales not resolvable by the Van Allen Probes. In addition, Geostationary Operational Environmental Satellite spacecraft data also indicate that these enhancements are consistent with relativistic electron injections. A radial diffusion model is shown to reproduce the PSD dynamics observed by the Van Allen Probes, once rapid variations at the simulation outer boundary are included, consistent with GPS data. This verifies that apparently “locally growing” peaks in PSD along high apogee satellite orbits can be produced by fast inward radial transport without requiring the action of any local acceleration processes.

In this work, we investigate co-seismic ionospheric disturbances (CSIDs) generated by the M8.8 earthquake of 29 July 2025 east of Petropavlovsk-Kamchatsky, Russia. By combining Ionosonde, global navigation satellite system slant TEC (sTEC) measurements, seismic waveforms, and time-distance (TTD) analysis, we track earthquake-induced perturbations across five azimuthal sectors extending from the western Pacific to the American west coast. We detected CSIDs with velocity 2.95–3.23 km/s linked to Rayleigh surface waves and associated acoustic waves, with Rayleigh-wave velocities of 3.46–3.87 km/s. Multiple-cusp signatures are identified on ionograms, indicative of vertical electron density perturbations associated with Rayleigh waves. Tracking nodes of these MCS perturbations across consecutive profiles yield apparent vertical velocities of 411–880 m/s, providing approximate constraints on upward propagation. sTEC-derived CSID velocities show good agreement with MCS-inferred speeds, ranging from 2.42 to 3.91 km/s, while delays of 8–18 min relative to Rayleigh-wave arrivals reflect acoustic coupling and ionospheric propagation. This study highlights the anisotropic propagation of earthquake-driven ionospheric disturbances and underscores the value of a multi-instrument approach in resolving both horizontal and vertical dynamics of CSIDs.

During the Mother's Day Storm, the most intense storm of the last 20 years, with a peak Dst of less than −400 nT, the Macau Science Satellite-1 observed the penetration of relativistic electrons of energies greater than 1 MeV into the inner radiation belt at Low Earth Orbit (LEO). The arrival of the MeV electrons was observed to occur instantaneously following the Dst minimum, with their continuous enhancement in the South Atlantic Anomaly over 7 days in the recovery phase reaching L $��=�$ 1.5. The so-called impenetrable barrier, previously estimated to be located at L $��=�$ 2.8 during the Van Allen Probes' era, has been significantly violated. A combined analysis of observations with Arase data at mid-latitude reveals the evolution of electron spectrum and pitch angle distribution for the first time, including zebra stripe patterns, an increase in electron flux near the loss cone, and a decrease in electron flux at higher pitch angles. These new results suggest that MeV electrons might undergo several steps to reach the inner radiation belt at LEO during this storm, which includes radial transport, radial diffusion, local acceleration and pitch angle scattering.