Journal of Geophysical Research: Space Physics最新文献

The Wideband Data instrument is part of the Cluster spacecraft Wave Experiment Consortium. Its primary data path is a direct connection to the spacecraft data handling system providing real time downlink to the ground stations of the Deep Space Network and Panska Ves Observatory. However, it was recognized during the mission design phase that this link may not always be available, especially given that simultaneous data acquisition from the four Cluster spacecraft required the use of four ground stations. Therefore, a secondary data path at reduced bit rate was included whereby the data was transferred to the Digital Wave Processor instrument and then to the spacecraft Solid State Recorder. Given that available resources were limited, both for onboard hardware and within the spacecraft assembly, integration and testing program, the design of this backup data path was less than optimal. Although it was verified during ground testing that data could be acquired via this route, the design did not make the best use of the available telemetry bandwidth, and the timing accuracy was too limited to support some multi-spacecraft observations. This paper describes work around solutions to optimize bandwidth utilization and timing accuracy. These involve patches to the onboard software of the Digital Wave Processor instrument and ingenious signal processing on the ground.

Dipolarization fronts (DFs), ion-scale magnetic-dipolar transients in the magnetotail, are favorable regions for the generation of various types of plasma waves, which are important for energy transport and dissipation in the magnetosphere. The plasma waves hitherto reported near the DFs are typically low-frequency (lower than electron cyclotron frequency) modes. Here, we report MMS observations of high-frequency waves, including Langmuir and upper hybrid waves near the electron plasma frequency, inside flux pileup regions behind the DFs. Using MMS high-cadence data, we revealed that the Langmuir waves were possibly generated by local electron beams and rapidly thermalized the beams, and the upper hybrid waves, which were associated with perpendicularly anisotropic electrons, may propagate from other regions. These waves can drive localized energy transfer and accelerate local electrons at a rate of ∼1.5 eV/s, indicating that the high-frequency waves can play a role in wave-particle energy transfer near the DFs.

High-speed jets (HSJs) are transient phenomena characterized by significant enhancement of magnetosheath dynamic pressure. They are capable of traversing the magnetosheath and impinging upon the magnetopause, triggering a diverse array of geoeffects. However, the evolution of HSJs during their propagation from the bow shock to the magnetopause still remains unclear. Leveraging multi-satellite data from MMS (2015–2023), THEMIS (2008–2023), and Cluster (2001–2020), we have compiled a comprehensive data set of nearly 40,000 HSJs to statistically study the velocity evolution of HSJs from the bow shock to the magnetopause for the first time. It is shown that the occurrence rate of HSJs depends on their relative positions within the magnetosheath, peaking in the middle region. Typically, in the GSE coordinates, as HSJs penetrate into the magnetosheath, the $��V_x�$ component gradually decreases until they reach the magnetopause, where HSJs are deflected and their $��V_y�$ and $��V_z�$ components are enhanced. Meanwhile, some HSJs are redirected backwards owing to rebounce of the magnetopause, resulting in the sunward flow. Notably, the velocity-direction distribution of HSJs in the $��\left(��y�,�z��\right)�$-plane is largely isotropic overall yet exhibits a subtle dusk-favored asymmetry. This distribution aligns with the background flow throughout the evolution of HSJs, a feature that is consistent with the outcomes of 3-D global simulations. This strong consistency implies HSJ transverse velocity tends to align with the ambient magnetosheath flow even early in their evolution. Our study provides some new insights in better understanding the evolution of HSJs within the magnetosheaths of Earth and other planets.

Thermosphere Ionosphere Electrodynamics General Circulation Model was used to investigate the underlying physical processes of the thermospheric and ionospheric vortex-like structure over East Asia region in November 2003 superstorm. Horizontal neutral winds with a vortex configuration modulate the composition (O/N₂) perturbations, forming a two-dimensional vortex-like structure. Vertical winds also have a positive contribution to the final shape of this structure in the altitude distribution. The ionospheric vortex-like structure below the ionospheric peak height (hmF2) is dominated by chemical effects (O/N₂ enhancements) and neutral wind transport, while it is directly controlled by the neutral wind transport above the hmF2. Decreases in plasma density within the core region of this structure, driven by E × B drifts at all altitudes, also contribute to its formation. Analysis of the forcing terms driving the wind vortex in the middle thermosphere reveals the dominant role of pressure gradients, alongside the combined action from the Coriolis force and horizontal momentum advection. In the upper thermosphere, the ion drag becomes significant, but only partially offsets the substantial positive effects of pressure gradients. Furthermore, controlled numerical experiments demonstrate that the storm intensity is not the single trigger mechanism for this structure. Instead, the asymmetrical prevailing circulation is more beneficial to the formation of the vortex-like structure. The storm onset time also affects the formation and location of this structure, although it is more likely to appear near the magnetic poles, primarily in the American and East Asian sector.

During the 21–22 January 2005 magnetic storm, the FAST satellite observed warm (< few keV) ions in discrete energy bands on the dayside at ∼3,000 km altitude for more than 6.5 hr. We suggest that the ionospheric energy-banded ions represent the low-altitude edge of the warm plasma cloak observed simultaneously by magnetospheric satellites. This is a clear example of the multi-species ion energy bands (10 eV to several keV) observed during strong magnetic storms by the FAST satellite, stretching from the diffuse auroral region to the plasmapause with lifetimes up to 12 hr. The close association of these energy-banded ions with magnetic storms, their broad latitudinal extent, and the presence of multiple ion species in the same energy band, rather than at the same velocity, indicate that this is a distinct phenomenon from other types of energy-banded ions. During the 21–22 January 2005 magnetic storm, the dayside ion energy band structures, centered at 10 eV (H⁺), 40 eV (H⁺ and He⁺), and 160 eV (H⁺, He⁺, and O⁺), were consistent with a “time-of-flight and velocity filter” formation process acting on a near-cusp, impulsive outflow of a <200 eV multi-species ion-source population, poleward and in the same hemisphere as FAST. Understanding the sources and dynamics of warm energy-banded ions and their linkage to the warm plasma cloak is important because during superstorms these ions are transported to L values as low as L ∼ 1.2 in the dawn sector, significantly altering the energetics of the mid-latitude ionosphere.

Understanding the formation, progression, and global impact of Large Scale (LS) Traveling Ionospheric Disturbances (TIDs) is a long-standing challenge in global space weather research. At high latitudes, the magnetosphere injects significant energy into the Ionosphere-Thermosphere (I-T) system through Joule heating, auroral particle heating, and ion drag. Traveling Atmospheric Disturbances (TADs) are a commonly observed thermospheric response to magnetospheric energy entering the I-T system. These atmospheric waves are believed to drive a similar wave response in the ionosphere, known as TIDs. Large-Scale Traveling Ionospheric Disturbances (LSTIDs) commonly travel from the equatorward edge of the auroral oval into the opposite hemisphere. This study examines the impact of LSTIDs on the topside equatorial ionosphere using a combination of observational and modeling methods. The geomagnetic storm that occurred on 25–26 March 2014 is used as a case study, because it contains a conjunction between two satellites that permits an analysis of the altitudinal differences in LSTIDs. The variations seen in the observations are then explored using I-T model runs, which allow for a detailed analysis of the LSTID variations and their drivers. The model results qualitatively agree with the satellite observations, and demonstrate that it is possible for LSTIDs to reach the topside ionosphere at low latitudes through variations in the field-aligned plasma drifts that are caused by the field-aligned component of the neutral wind modifying the plasma density peak heights, resulting in conjugate differences that affect the field-aligned plasma pressure gradient.

Atmospheric gravity waves (GWs) are believed to transport energy and momentum between different regions of the atmosphere. Historically, observations of these waves from both ground and space have been relatively abundant at altitudes up to the lower thermosphere, and somewhat less abundant in the upper thermosphere and F-region ionosphere altitudes. Much of what is known of the typical properties and occurrence of these waves at thermospheric altitudes has been inferred from their impacts on the ionospheric density and motion, as direct observations of the neutral atmosphere have been less prevalent. Gravity waves in the middle thermosphere, from ∼120–200 km altitude, have rarely been observed directly and as such, their properties at these altitudes are less well documented. NASA's Global-Scale Observations of the Limb and Disk (GOLD) mission makes observation of the middle thermosphere during daytime. During dedicated campaigns, GOLD has been able to observe GWs in this region. This study leverages 22 such campaigns during quiet geomagnetic conditions and low to moderate solar activity levels. Waves were observed with typical periods ∼2–4 hr. Leveraging ground-based observations, the wavelengths were identified to be between ∼1,500–5,000 km, with phase speeds ∼150–600 m/s. The waves observed were seen to propagate primarily meridionally, in agreement with prior daytime mid-latitude observations. Using observations of the background wind, the energy and momentum fluxes carried by these waves were found. During the quiet conditions observed, the waves were seen to transport energy flux over a wide range of latitudes.

Ionospheric disturbances caused by acoustic waves (AW) are observed by Global Navigation Satellite Systems (GNSS) measures of total electron content (TEC). AWs that propagate to the ionosphere can be caused by ground-based explosions, including seismic events. These events often occur in remote regions like the open ocean. Identifying an AW and locating the source of the AW from GNSS TEC measurements is challenging due to several variables between events such as propagation metrics, line of sight geometry, and ionization levels. This becomes especially difficult with a sparse network and limited signal coverage, typical of remote regions. We propose here the use of a deep learning, ionospheric anomaly detection algorithm and a geolocation algorithm capable of identifying atypical ionospheric behavior after a seismic event and estimating the source location. We outline the development of this algorithm and test results over the months of May and June 2023 for five GNSS receivers in the South Pacific. Results show the successful detection of two open ocean M7.7 and M7.1 earthquakes. Three TEC measurements detected as anomalous from the M7.7 earthquake event were used to estimate the epicenter of the earthquake, resulting in a source geolocation of $���23.55�°��$S, $���171.64�°��$E, a discrepancy of $���0.34�°��$ in latitude and $���0.90�°��$ in longitude, $���\pm �0.2�°��$. This research demonstrates the feasibility of AW detection and source geolocation from a sparse GNSS network over open ocean.