Earth, Planets and Space最新文献

This work brings together the contents of previously disparate databases of absolute ground geomagnetic observations, both historic and ongoing, to process the data consistently into a coherent and accessible format for researchers. This includes converting reported time resolutions and coordinate systems into a uniform format, and applying all documented observatory baseline changes to the data records, to create a single unified vector time series of monthly mean values for each geomagnetic observatory. The data are made available freely and anonymously to researchers via a web service, updated on a monthly basis with the latest definitive and non-definitive observations reported to the World Data Centre for Geomagnetism (Edinburgh) and INTERMAGNET or Tromsø Geophysical Observatory, respectively. The current database covers 327 observatories worldwide, with observations from 1883 up until present. A separate effort involved digitising tables of monthly means in the 1841-1925 yearbooks of the Royal Observatory, Greenwich, United Kingdom and converting to homogeneous units. The resulting data represent some of the earliest magnetic data at monthly time resolution and may be of use to future studies. However, they cannot be incorporated into the monthly means database as the field vector information is incomplete; we publicise them here instead.

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Abstract: Subauroral ion drift (SAID) is a narrow and rapid westward ion flow observed in the subauroral ionosphere during geomagnetic storms and substorms. It is more localized and intense than subauroral polarization streams (SAPS), typically appearing equatorward of auroral boundaries and often associated with midlatitude troughs. This study analyzes ion drifts and plasma density variations using DMSP F16, F17, and F18 data from June 1, 2013, in the Southern Hemisphere. Using multi-satellite observations from three DMSP spacecraft, we systematically examine the spatiotemporal evolution of a SAID event and its associated midlatitude troughs, focusing on their relation to geomagnetic storm phases and substorm activity. We develop an ad hoc empirical model that reproduces SAID spatial distribution and temporal evolution by establishing a quantitative relationship between SAID velocity and the AE index. From the results, we present two key findings: first, we identified a previously unreported two-stage development pattern of SAID: equatorward expansion with minimal width change and moderate potential drop in the early main phase, followed by latitudinal stabilization, width variation, and stronger electric fields in the late main phase. Second, we newly identified that the midlatitude trough developed through three distinct stages: mild density gradient associated with the initial AE increase, sharp density drop at the plasmapause boundary after the first AE decrease, and persistent deep trough after first AE peak and throughout the second AE peak lasted for three hours. These findings and our empirical modeling approach provide new quantitative insights into the distinct temporal evolution patterns of SAID and midlatitude troughs, advancing further understanding of the connection between ionospheric disturbances and geomagnetic storms.

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We present results of a study of post-midnight equatorial spread F (ESF) events over the Jicamarca Radio Observatory (JRO) that examined unambiguous radar measurements of event origin in the American sector. Our analysis considers variations in post-midnight ESF generation due to changing seasonal, solar, and geomagnetic conditions. We analyzed 396 nights of observations made with the 14-panel version of the Advanced Modular Incoherent Scatter Radar (AMISR-14) between July 2021 and August 2023. We leveraged the 10-beam AMISR-14 mode, which effectively measures ~ 400 km zonally of the equatorial F-region ionosphere, to identify and classify post-midnight ESF as either local (i.e., generated within the instrument field of view) or non-local (i.e., generated outside the instrument field of view). Our results for the occurrence rates of post-midnight ESF exhibit a strong seasonal dependence, with maximum values in June solstice and minimum values for equinoxes. The results also show the post-midnight ESF occurrence rates are anticorrelated to the solar flux conditions. As for geomagnetic activity, the results indicate that occurrence rates decrease considerably under geomagnetically quiet conditions. The combination of these seasonal, solar flux, and geomagnetic activity influences suggests the weakened downward plasma drifts late at night during June solstice conditions can be reversed to upward drifts by contributions from disturbance drifts. In the case of upward drifts caused by geomagnetic disturbances, the reversed upward post-midnight drifts may then contribute to conditions favoring ESF development provided that a prompt penetration or disturbance dynamo electric field with appropriate polarity, even from modest geomagnetic activity, is present. In support of this proposed post-midnight ESF generation mechanism, we also present and discuss simultaneous AMISR-14 and collocated incoherent scatter radar measurements of a June solstice 2023 event. Perhaps most importantly, our results show the occurrence rates of local and non-local post-midnight ESF as observed with AMISR-14 are nearly identical. That is, local events were observed effectively as often as non-local events, and vice versa, under all seasonal, solar, and geomagnetic conditions. Therefore, data-driven forecasting approaches relying exclusively on local (i.e., "overhead") measurements of ionospheric/thermospheric conditions may not always be well-suited to reproducing the observed ESF phenomenology.

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Abstract: The SS-520-3 sounding rocket was launched on November 4th, 2021 as part of the Grand Challenge Initiative - Cusp from Ny-Ålesund, Svalbard. The rocket was launched into the cusp ionosphere during the main phase of a geomagnetic storm. In this study we utilize two low energy particle analyzers as well as a multi-needle Langmuir probe and an impedance probe as part of the rocket payload. This study aims to provide an overview of the flight conditions from a range of ground-based instruments and scintillation receivers. We were able to confirm that the rocket entered the cusp through the poleward edge at around ${74}^{\circ }$ of northern geographic latitude. Additionally, the rocket encountered polar cap patches (PCP), as well as a patch within the cusp (CP) and a newly-formed tongue of ionisation (TOI). Analysis of the density variations within different scale sizes show enhancements within meter-size and kilometer-size scales on the edges of PCP, within the CP and TOI. Overall, the enhancements within the variations on all sizes, as well as enhancements of the electron density were significantly higher within the CP and TOI in comparison to the PCP, though all structures were encountered at similar altitudes. The strongest enhancements were found on the poleward edge of the TOI, corresponding to strong fluctuations within the electron density. The TOI also had the largest enhancements within gradients of kilometer-size in comparison to meter-sizes. As the TOI is convecting with respect to the background plasma, the edges are susceptible to instabilities like the Kelvin-Helmholtz instability (KHI) and Gradient-Drift instability (GDI), giving rise to plasma density structures on several scale sizes.

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Frontal waves, characterized by sharp boundaries of airglow jump accompanied by following undulations, were detected using machine learning techniques, and their variability was examined. Frontal waves are thought to be manifestations of ducted waves called mesospheric bores or "wall" waves (large-amplitude gravity waves). The YOLOv3 machine learning model, short for "You Only Look Once version 3," was trained to detect frontal wave events in Day/Night Band (DNB) data from the Visible/Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. The YOLOv3 detector was trained with DNB images, including manually labeled objects of 756 unique frontal waves. The model achieved 83.19% of average precision (AP) for frontal wave event detection during the testing phase. Utilizing the trained model, 1,150 frontal wave events were identified out of all available 515,187 moonless images from Suomi NPP VIIRS/DNB from January 2012 to June 2023. Over the past eleven years, the monthly occurrence of frontal wave events has gradually decreased from approximately 15 in 2012 to around 5 in 2022. Frontal waves exhibit a high occurrence peak at equatorial latitudes and weaker occurrence peaks at winter mid-latitudes. In these regions, the migrating diurnal and semidiurnal tides exhibit large temperature amplitudes, which could create a favorable environment for ducted waves or mesospheric bores, such as a temperature inversion layer. Frontal waves detected in this study show higher occurrences in regions where conditions favor the formation of ducted waves or mesospheric bores.

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 The 2024 ${\text{M}}_{\text{w}}$ 7.5 Noto earthquake, Japan, was preceded by an intense seismic swarm thought to be driven by upward fluid migration. Crustal seismic velocities vary with external perturbations caused by earthquakes, and the presence of pressurized fluids in the crust amplifies the resulting coseismic velocity change. Hence, we characterize subsurface fluid by measuring the coseismic velocity change associated with the 2024 mainshock. For this purpose, we perform multi-frequency-band ambient noise seismic interferometry using data from permanent and temporary seismic stations. Significant coseismic velocity drops are observed, with an average decrease of about 0.5% inside the Noto peninsula, reaching 0.6-0.8% in the regions near the coseismic slip peaks. The observed velocity drops inside the peninsula correlate well with the modeled static-stress-change-induced velocity drops and peak ground velocity (PGV) and acceleration (PGA) as proxies of dynamic stress change. However, their respective contribution to the observed coseismic velocity drop remains unclear because of the similarities in their spatial pattern. Outside the Noto Peninsula, the observed velocity drops average around 0.1%, which is predominantly attributed to dynamic stress changes from passing waves because modeled static stress changes are negligible at these great distances. Although the addition of temporary stations significantly increases the resolution of the velocity drop measurements in the pre-mainshock swarm zone, our results exhibit no large velocity drop anomaly in this region, suggesting that the amount of pressurized fluids in the shallow crust down to $\sim$ 2.5 km depth is not anomalously large. This implies that the upward migration of fluids preceding the mainshock is likely confined to greater depths.

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Supplementary information: The online version contains supplementary material available at 10.1186/s40623-025-02177-x.

Developing techniques to monitor volcanic activity from safe distances is crucial for advancing scientific knowledge while protecting the safety of field personnel. One of the most demanding tasks in this context is the measurement of soil gas emissions, which offer valuable insights into fluid migration through the shallow crust and act as an early indicator of volcanic unrest and potential eruptive activity. Traditional soil degassing measurements commonly require two operators to be physically present with the instrument, sometimes exposing them to hazardous conditions. In this study, we present a new method for performing soil degassing measurements from a safe distance, using a customized Remotely Piloted Aircraft System (RPAS). This drone-based approach was designed to carry out accumulation chamber measurements in hazardous or otherwise inaccessible areas. We tested the system at four locations around the active crater of Poás Volcano in Costa Rica, where we collected data on CO₂ and H₂O fluxes, along with soil temperature and moisture. Our results reveal spatial variability in gas emissions and surface conditions across the study sites. A site located on the crater rim (Site 1) showed the highest CO₂ and H₂O fluxes, indicating active gas release possibly associated with structural features. A second site, located within the crater (Site 2), exhibited elevated H₂O flux without detectable CO₂, suggesting localized processes related to moisture transport. Our experiment on another crater site (Site 3) produced a complete and high-quality dataset, demonstrating the operational success of the method. In contrast, measurements at the last crater site (Site 4) were affected by chamber sealing issues and potentially by the influence of volcanic gas plumes. While the experiment faced several challenges, including imperfect ground-sensor contact as well as occasional telemetry interruptions, it successfully demonstrated the feasibility of using drones for soil degassing surveys. Based on these findings, we identify specific areas for improvement and propose future directions to enhance the system reliability and performance. Overall, this method offers a promising tool for extending soil gas measurements to hazardous or hard-to-reach environments, contributing to safer and more comprehensive monitoring of active volcanic systems.

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Supplementary information: The online version contains supplementary material available at 10.1186/s40623-025-02303-9.

Dehydroxylate I, a product of the thermal decomposition of serpentine, has been observed in heated carbonaceous chondrite meteorites. To better understand the occurrence of dehydroxylate I on carbonaceous asteroids, we have experimentally heated the carbonaceous chondrite Murchison from 400 to 550 °C at 25°C temperature steps, during which in situ micro X-ray diffraction (µXRD) patterns were collected using synchrotron radiation. µXRD was utilized such that the dehydroxylate I's diffraction pattern could be isolated and characterized. This was successfully achieved, with the phase being detected at 400 °C. A diffraction pattern for dehydroxylate I was isolated at 525 °C, where it displayed crystallographic similarities to the mineral carlosturanite. We propose dehydroxylate I is produced when gaps form in serpentine's tetrahedral sheet during its breakdown, which is consistent with previous studies on serpentine decomposition. The d-spacings for dehydroxylate I described here can be used to better identify it in natural and experimentally heated terrestrial and meteoritic samples.

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BepiColombo, the joint ESA/JAXA mission to Mercury, was launched in October 2018 and is scheduled to arrive at Mercury in November 2026 after an 8-year cruise. Like other planetary missions, its scientific objectives focus mostly on the nominal, orbiting phase of the mission. However, due to the long duration of the cruise phase covering distances between 1.2 and 0.3 AU, the BepiColombo mission has been able to outstandingly contribute to characterise the solar wind and transient events encountered by the spacecraft, as well as planetary environments during the flybys of Earth, Venus, and Mercury, and contribute to the characterisation of the space radiation environment in the inner Solar System and its evolution with solar activity. In this paper, we provide an overview of the cruise observations of BepiColombo, highlighting the most relevant science cases, with the aim of demonstrating the importance of planetary missions to perform cruise observations, to contribute to a broader understanding of Space Weather in the Solar System, and in turn, increase the scientific return of the mission.

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We present a candidate mean secular variation (SV) model for the 2025.0 $-$ 2030.0 period. The forecasted SV is produced with a data assimilation (DA) system built around a simple frozen-flux model of the core flow and magnetic field near the core-mantle boundary (CMB). An Ensemble Kalman Filter (EnKF) and smoother (EnKS) are used to assimilate Gauss coefficients from the Kalmag field model, to estimate a core flow which is then used to predict changes in the magnetic field. This forecast methodology is tested against past 5-year periods where it is found to be effective in predicting mean SV, and is superior to an otherwise identical setup using an EnKF alone (no EnKS). The inferred core flow is examined and is seen to exhibit structures consistent with the eccentric gyre and westward drift found in traditional inversions. While this study presents an SV candidate, its secondary purpose is to explore and highlight the potential of the EnKS methodology in understanding the geodynamo. Notably, the EnKS algorithm we use requires no adjoint for the model and can be implemented into already existing EnKF-based systems. The ease of implementation and improvement provided by the EnKS make it a desirable addition to other geomagnetic data assimilation systems, particularly those built around full, 3-D numerical dynamo models, for which the production and maintenance of an adjoint can be challenging.

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