Earth, Planets and Space最新文献

{"title":"IGRF-14 secular variation prediction from core surface flow acceleration.","authors":"Frederik Dahl Madsen, Ciarán D Beggan, William J Brown, Richard Holme, Jonas Bregnhøj Lauridsen, Kathryn A Whaler","doi":"10.1186/s40623-025-02347-x","DOIUrl":"10.1186/s40623-025-02347-x","url":null,"abstract":"<p><strong>Abstract: </strong>The International Geomagnetic Reference Field (IGRF) has been regularly updated since its inception in 1965. Every recent iteration contains an estimate of the geomagnetic secular variation (SV), for the intermediate years between iterations. We submit a candidate model for the geomagnetic secular variation (SV) for the period 2025-2030 for the 14^th generation of the IGRF. Given the recent evidence in the geomagnetic SV record for core surface waves, we forecast SV based on the periodic behaviour of core surface flow acceleration. We obtain an advective core surface flow model, in terms of poloidal and toroidal flow coefficients, from spatial gradients of SV geomagnetic virtual observatory data from the low-Earth orbiting CHAMP and Swarm missions from January 2001 to January 2010, and April 2014 to January 2024, respectively. From these, we calculate the flow acceleration coefficients from the first time-derivative. This assumes the flow is spatio-temporally simple, without imposing any physical constraints on its geometry. We fit each acceleration coefficient with a sinusoidal function, which is used to extrapolate 6 years into the future. These sinusoidally varying acceleration time series are integrated over time to obtain the core flow coefficients, which are then used to predict the average advected SV over the 5-year IGRF period. We recreate previous IGRF predictions using our CHAMP-based flows to validate our methodology, which we find to outperform previous IGRF iterations, and use the Swarm-based flows to forecast the SV for IGRF-14. Our Swarm-based model predicts sudden changes in SV-also known as geomagnetic jerks-in 2024 in the Equatorial Pacific, and in 2028 in the region around central Africa. Although the IGRF SV is a snapshot over a 5-year period, allowing for periodic behaviour offers potential improvements over other methods of prediction.</p><p><strong>Graphical abstract: </strong></p><p><strong>Supplementary information: </strong>The online version contains supplementary material available at 10.1186/s40623-025-02347-x.</p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"29"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12891054/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146178568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How do core surface flow models vary when inverted from IGRF-14 candidate field models?","authors":"H F Rogers, M Mandea","doi":"10.1186/s40623-025-02307-5","DOIUrl":"https://doi.org/10.1186/s40623-025-02307-5","url":null,"abstract":"<p><p>The International Geomagnetic Reference Field (IGRF) model is a series of models that describe the large scale magnetic field measured at the Earth's surface. It is used by a wide range of scientists and industries, including in navigation, space weather applications, and resource exploration. The 14th generation, IGRF-14, is the result of an international collaboration over 19 different lead research groups. This new generation provides a definitive model of the main magnetic field (MF) for the epoch 2020.0, a prediction of the MF for 2025.0, and a predicted average annual time variation of the magnetic field for 2025.0 <math><mo>-</mo></math> 2030.0. The first time derivative of the magnetic field, known as secular variation, (SV) is linked to the flow at the top of Earth's outer core. As such, the ensemble of IGRF-14 candidate models can be used to investigate predicted core flow variability between 2020.0 and 2030.0. We use the pygeodyn Python package using the AR-1 'dense' methodology, the 71% geodynamo prior, and keep all inversion parameters fixed to ensure that differences in inferred flow arise solely from variations from the IGRF candidate models. Our results demonstrate that while all candidates produce broadly similar flow spectra for all degrees, candidates that deviate most from the median IGRF model also show the largest differences in flow. In all cases, the flow speed difference remains below 25% of the maximum flow speed of the Huber-weighted mean model in space, with most discrepancies occurring at small spatial scales. The greatest flow uncertainty appears over the Pacific and in the polar regions, where constraints are weaker. Finally, we assess the impact of the maximum spherical harmonic degree truncation of the SV candidate models by comparing two SV candidates truncated at spherical harmonic degree 13 instead of 8. Increasing the truncation degree of SV alters the flow spectral energy at all degrees and increases the maximum flow speed by up to 31%, despite the flow maps remaining highly correlated. This study supports the idea of raising the spherical harmonic truncation degree to 13 for the SV prediction component of the IGRF.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"39"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12948799/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147324879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A database of geomagnetic observatory monthly means: from historic to the satellite era.","authors":"William Brown, Susan Macmillan, Eleanor Maume, Eliot Eaton","doi":"10.1186/s40623-025-02316-4","DOIUrl":"10.1186/s40623-025-02316-4","url":null,"abstract":"<p><p>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.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"7"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12804219/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145997476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Model calculations for neutron-induced reactions in meteorites and planetary surfaces.","authors":"Ingo Leya","doi":"10.1186/s40623-025-02358-8","DOIUrl":"10.1186/s40623-025-02358-8","url":null,"abstract":"<p><p>This study investigates the capabilities of the GEANT4 Monte Carlo toolkit to quantitatively predict neutron production, neutron transport, and nuclide production by neutron capture reactions in cosmochemical relevant objects. The model reproduces neutron densities measured in the lunar surface within the experimental uncertainties, which is a major improvement compared to earlier studies. Since, for many applications in meteorites and planetary surfaces, nuclide production by neutron capture is of importance, the production of <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>41</mn></mmultiscripts> </math> Ca and <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>60</mn></mmultiscripts> </math> Co is studied as an example. In addition, shifts in the stable isotope ratios <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>157</mn></mmultiscripts> </math> Gd/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>160</mn></mmultiscripts> </math> Gd, <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>158</mn></mmultiscripts> </math> Gd/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>160</mn></mmultiscripts> </math> Gd, <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>149</mn></mmultiscripts> </math> Sm/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>152</mn></mmultiscripts> </math> Sm, and <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>150</mn></mmultiscripts> </math> Sm/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>152</mn></mmultiscripts> </math> Sm (and combinations thereof) are modeled and compared to experimental data. The model describes experimental <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>41</mn></mmultiscripts> </math> Ca activity concentrations in different types of meteorites and the lunar surface within the uncertainties. In contrast, it fails to describe <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>60</mn></mmultiscripts> </math> Co activity concentrations. In addition, it is difficult to consistently model the isotope shifts <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>157</mn></mmultiscripts> </math> Gd/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>160</mn></mmultiscripts> </math> Gd and <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>150</mn></mmultiscripts> </math> Sm/ <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>152</mn></mmultiscripts> </math> Sm in Apollo 15 drill core samples. The observed trends depend on the temperature of the irradiated object and are more pronounced for colder temperatures. Since the observed discrepancies are likely related to the shape of the neutron spectra, self-shielding effects by, e.g., <math><mmultiscripts><mrow></mrow> <mrow></mrow> <mn>56</mn></mmultiscripts> </math> Fe, might be of importance and some of the consequences are discussed.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"27"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12891260/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146178695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Global data-driven predictions of seasonal non-tectonic signals in vertical GNSS displacement time series from non-tidal surface loading data.","authors":"Kaan Çökerim, Henryk Dobslaw, Kyriakos Balidakis, Laura Jensen, Carlos Peña, Jonathan Bedford","doi":"10.1186/s40623-026-02385-z","DOIUrl":"10.1186/s40623-026-02385-z","url":null,"abstract":"<p><p>Daily displacement time series from Global Navigation Satellite Systems (GNSS) are frequently used to study deformations of the Earth's surface due to a wide range of different geophysical processes. The recorded deformations result from tectonic activity or non-tectonic processes like volcanism, groundwater fluctuations and atmospheric loading. In addition, local disturbances of the antenna (e.g., snow cover, thermoelastic effects of the monumentation) and artifacts from GNSS processing (e.g., draconitic signals) are sometimes prominently included in coordinate time series. We use a Temporal Convolution Network (TCN) to predict non-tectonic vertical GNSS displacements on a global scale from physics-based non-tidal loading products. We train our model on a global dataset with more than 11,000 GNSS stations from the Nevada Geodetic Laboratory, active from January 2002 until June 2024, and evaluate the performance against independent estimations. Across the hold-out dataset, our TCN derives non-tidal loading GNSS signatures that when compared to the non-tectonic GNSS signal results in a global average reduction in RMSE of 4.7 % with respect to the numerical non-tidal loading models. This approach presents an initial step towards a data-driven complement to physics-based numerical loading models, improving the isolation of non-tectonic signals in GNSS time series and validation of numerical non-tidal loading models.</p><p><strong>Graphical abstract: </strong></p><p><strong>Supplementary information: </strong>The online version contains supplementary material available at 10.1186/s40623-026-02385-z.</p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"56"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13021762/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147572799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The spatiotemporal development of the midlatitude troughs and subauroral ion drift during a geomagnetic storm observed by multiple DMSP satellites.","authors":"Heechan Cha, Jerry Goldstein, Dhirendra Kataria, Yukitoshi Nishimura, Keiichi Ogasawara","doi":"10.1186/s40623-025-02349-9","DOIUrl":"10.1186/s40623-025-02349-9","url":null,"abstract":"<p><strong>Abstract: </strong>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.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"78 1","pages":"14"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12847133/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146084898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of local and non-local post-midnight equatorial spread-F generation based on long-term AMISR-14 observations.","authors":"Alexander A Massoud, Fabiano S Rodrigues, Jonas Sousasantos, Karim M Kuyeng, Danny E Scipión, Carlos Padin","doi":"10.1186/s40623-025-02319-1","DOIUrl":"https://doi.org/10.1186/s40623-025-02319-1","url":null,"abstract":"<p><p>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.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"77 1","pages":"189"},"PeriodicalIF":2.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12660415/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145647758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine-learning detection and variability of mesospheric frontal waves observed by VIIRS day/night band.","authors":"Yuta Hozumi, Jia Yue, Seraj Al Mahmud Mostafa, Chenxi Wang, Jianwu Wang, Sanjay Purushotham, Steven D Miller","doi":"10.1186/s40623-025-02308-4","DOIUrl":"10.1186/s40623-025-02308-4","url":null,"abstract":"<p><p>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.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"77 1","pages":"179"},"PeriodicalIF":2.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12615530/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145539514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Plasma structuring within an expanded polar cap and cusp studied with the SS-520-3 sounding rocket.","authors":"L M Buschmann, K Asamura, L B N Clausen, Y Jin, H Kojima, A Kumamoto, S Kurita, Y Ogawa, K Oksavik, Y Saito, A Spicher, S Yokota, W J Miloch","doi":"10.1186/s40623-025-02189-7","DOIUrl":"https://doi.org/10.1186/s40623-025-02189-7","url":null,"abstract":"<p><strong>Abstract: </strong>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 <math><msup><mn>74</mn> <mo>∘</mo></msup> </math> 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.</p><p><strong>Graphical abstract: </strong></p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"77 1","pages":"76"},"PeriodicalIF":3.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12106493/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144173128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coseismic crustal seismic velocity changes associated with the 2024 M_W 7.5 Noto earthquake, Japan.","authors":"Nicolas Paris, Yuji Itoh, Florent Brenguier, Qing-Yu Wang, Yixiao Sheng, Tomomi Okada, Naoki Uchida, Quentin Higueret, Ryota Takagi, Shin'ichi Sakai, Satoshi Hirahara, Shuutoku Kimura","doi":"10.1186/s40623-025-02177-x","DOIUrl":"https://doi.org/10.1186/s40623-025-02177-x","url":null,"abstract":"<p><p> The 2024 <math><msub><mtext>M</mtext> <mtext>w</mtext></msub> </math> 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 <math><mo>∼</mo></math> 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.</p><p><strong>Graphical abstract: </strong></p><p><strong>Supplementary information: </strong>The online version contains supplementary material available at 10.1186/s40623-025-02177-x.</p>","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"77 1","pages":"51"},"PeriodicalIF":3.0,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12011933/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143958620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}