Journal of Geophysical Research: Space Physics最新文献

{"title":"The Impact of Geomagnetic Activity on the Height-Dependent Ionospheric Delay in Relation to Solar Activity","authors":"Rajesh Vaishnav,&nbsp;Christoph Jacobi,&nbsp;Erik Schmölter,&nbsp;Hanna Dühnen","doi":"10.1029/2025JA034221","DOIUrl":"https://doi.org/10.1029/2025JA034221","url":null,"abstract":"<p>Previous research has indicated that geomagnetic activity plays an important role in influencing the ionospheric delayed response to solar activity variations at the solar rotation time scale depending on solar activity conditions. In this study, we employed the Thermosphere-Ionosphere-Electrodynamic General Circulation Model to investigate the vertically resolved impact of geomagnetic activity on the ionospheric delay over the solar rotation period from 29 April to 25 May 2015. This time period was chosen due to its representative moderate solar and geomagnetic activity conditions. Our analysis revealed that the ionospheric delay increases with altitude due to geomagnetic activity and is more pronounced in the Southern Hemisphere than in the Northern Hemisphere. To further understand the underlying mechanisms responsible for the observed changes in ionospheric delay, we examined neutral species (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 <annotation> $O$</annotation>\u0000 </semantics></math> and <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>N</mi>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${N}_{2}$</annotation>\u0000 </semantics></math>), their ratio <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <mrow>\u0000 <mi>O</mi>\u0000 <mo>/</mo>\u0000 <msub>\u0000 <mi>N</mi>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left(O/{N}_{2}right)$</annotation>\u0000 </semantics></math>, and neutral temperature. The results show that thermosphere-ionosphere composition varies both vertically and horizontally in response to geomagnetic activity, and that these composition changes contribute to vertical variations in ionospheric delay.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034221","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Delayed Ionospheric Response to Solar Activity: Influence of Geomagnetic Activity","authors":"Rajesh Vaishnav,&nbsp;Christoph Jacobi,&nbsp;Erik Schmölter,&nbsp;Hanna Dühnen","doi":"10.1029/2025JA034151","DOIUrl":"https://doi.org/10.1029/2025JA034151","url":null,"abstract":"<p>The role of geomagnetic activity in the delayed response of the ionosphere along with the solar influences was investigated through a series of controlled simulations of the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model under conditions of moderate geomagnetic storms during varying solar activity. In addition, observed ionospheric total electron content data sets were used to investigate the ionospheric delay and to compare it with the model simulations. The ionospheric delay varies spatially and seasonally depending on the solar and geomagnetic activity conditions. The simulations show a global decrease in ionospheric delay during Northern Hemisphere spring, except at high-latitudes in the Northern Hemisphere under moderate geomagnetic activity. The delay increases in the Western Hemisphere during the winter season. We found that the ionospheric delay during the 27-day solar rotation period changes based on whether geomagnetic activity occurs before or after the peak solar rotation day. This study emphasizes the significance of considering the geomagnetic activity when calculating ionospheric delay.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034151","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Solar Flare-Induced Gradient Drift Instability Observed by SuperDARN HF Radars","authors":"S. Chakraborty,&nbsp;N. Nishitani,&nbsp;X. Shi,&nbsp;P. Ponomarenko,&nbsp;J. M. Ruohoniemi,&nbsp;J. B. H. Baker,&nbsp;A. J. Coster,&nbsp;I. Häggström","doi":"10.1029/2025JA033824","DOIUrl":"https://doi.org/10.1029/2025JA033824","url":null,"abstract":"<p>Solar flares are a rapid increase in solar irradiance, specifically in X-ray and Extreme Ultraviolet spectra, which enhances the ionization in the dayside ionosphere and creates Sudden Ionospheric Disturbances (SIDs). SIDs are known to create space weather impacts on traveling high frequency (HF: 3–30 MHz) radio waves, by disrupting the communication channels. In this study, we examine ionospheric scatters at dawn terminator, which stems from a severe X9.3 flare on 6 September 2017 peaked at 12:02 UT, utilizing SuperDARN HF coherent scatter radars and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) observations. Specifically, we are interested in the transients in the ionospheric electrodynamics at the sub-auroral latitude near the terminator stemming from the flare effect. Observations suggest that flare-induced density gradient likely favors the formation of gradient-drift instability near the dawn terminator, leading to the irregularities observed by the SuperDARN radars with line-of-sight (LoS) Doppler velocity reaching nearly 300 m/s. The flare amplifies the eastward TEC gradient near the dawn terminator by approximately 2–3 times compared to a geomagnetically quiet and non-flare day. The observed irregularities, attributed to flare-driven instabilities, exhibit a velocity consistent with the equatorial return flow of ionospheric Hall convection. In contrast to prior studies indicating decreased cross-polar-cap potential and associated ionospheric convection flow, our findings show the flare is followed by an increase in localized electric field near the dawn terminator, as depicted in radar LoS velocity.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evolution of the Mid-Latitude Red Aurora Over Northern China During the 5 November 2023 Geomagnetic Storm","authors":"Jianyun Liang,&nbsp;Jiyao Xu,&nbsp;Yongliang Zhang,&nbsp;Shun-Rong Zhang,&nbsp;Kun Wu,&nbsp;Wei Yuan,&nbsp;Yajun Zhu,&nbsp;Guozhu Li,&nbsp;Xiao Liu","doi":"10.1029/2024JA032729","DOIUrl":"https://doi.org/10.1029/2024JA032729","url":null,"abstract":"<p>This study presents novel observations of a mid-latitude red aurora event at 44°MLAT over Northern China during the 5 November 2023 geomagnetic storm, using simultaneous observations from ground-based instruments (630 nm all-sky imager (ASI) and ionosonde) at Mohe station (53.5°N, 122.4°E; MLAT = 44.32°N) and space-based satellites (Swarm and Defense Meteorological Satellite Program F17 and F18). The auroras displayed unusual dynamics, appearing north of the ASI field of view (FOV) at 1000 UT, disappearing at 1300 UT, then reappearing at 1400 UT with equatorward expansion (∼62 m/s) to reach 51°N (42°MLAT/2.3 L) and lasting ∼8 hr. Analysis indicated that the auroral characteristics resembled stable auroral red arc (SARc), including thermal excitation (electron temperatures &gt;3,000 K) and ionogram features (weak spread-F occurrence and reduced critical frequency). The auroras exhibited distinctive yet previously unreported properties of SARc, prompting their definition as SARc-like events. Specifically, the auroral emissions demonstrated clear additional contributions from ion precipitation (hundreds eV to tens keV ions) alongside thermal excitation of the typical SAR theory, and they were not fixed within the ionospheric trough unlike a narrow band of typical SARc pattern. The ionospheric trough at its equatorward edge exhibited synchronous equatorward motion. Concurrently, ionosonde echoes weakened and disappeared as the aurora and trough passed overhead, suggesting density depletion effects. Both the trough dynamics and ion precipitation likely drove electron temperature enhancements. These findings reveal new complexities in mid-latitude auroral physics requiring further investigation.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New Fit for the O+-O Collision Frequency Including Fine Structure Effects","authors":"A. P. Hickman","doi":"10.1029/2025JA034494","DOIUrl":"https://doi.org/10.1029/2025JA034494","url":null,"abstract":"&lt;p&gt;A new fit is presented for the oxygen ion-neutral collision frequency &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;ν&lt;/mi&gt;\u0000 &lt;mtext&gt;in&lt;/mtext&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${nu }_{text{in}}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;. The fit explicitly depends on the neutral temperature &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;T&lt;/mi&gt;\u0000 &lt;mi&gt;n&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${T}_{mathrm{n}}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;, which characterizes the thermal distribution of fine structure levels of O(&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;P&lt;/mi&gt;\u0000 &lt;mi&gt;J&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;,&lt;/mo&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;J&lt;/mi&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;0&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${P}_{J},,J=0$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;,1,2), and the reduced temperature &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;T&lt;/mi&gt;\u0000 &lt;mi&gt;r&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mfrac&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/mfrac&gt;\u0000 &lt;mfenced&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;T&lt;/mi&gt;\u0000 &lt;mi&gt;n&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;T&lt;/mi&gt;\u0000 &lt;mi&gt;i&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mfenced&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${T}_{mathrm{r}}=frac{1}{2}left({T}_{mathrm{n}}+{T}_{mathrm{i}}right)$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;, where &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;T&lt;/mi&gt;\u0000 &lt;mi&gt;i&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${T}_{mathrm{i}}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; is the ion temperature. A physically realistic fitting function adapted from the exact solution of a two-state system is constrained to approach plausible analytic models in the limits that &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 ","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034494","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Unseasonal Enhancements of Quasi-6.5-Sol Waves in the Southern Hemisphere of Mars During Major Dust Storms","authors":"Qiao Xiao,&nbsp;Zheng Ma,&nbsp;Yun Gong,&nbsp;Shaodong Zhang,&nbsp;Chunming Huang","doi":"10.1029/2025JA034132","DOIUrl":"https://doi.org/10.1029/2025JA034132","url":null,"abstract":"<p>Based on temperature data from the Mars Climate Sounder onboard Mars Reconnaissance Orbiter, this study investigates quasi-6.5-sol waves (Q6.5SWs) in the Southern Hemisphere (SH) of Mars from Mars Year (MY) 30 to MY 36. We report, for the first time, unseasonal enhancements of Q6.5SWs in the mid-to-high latitudes of the SH, coinciding with three early dust storm events in MY31, MY34, and MY36. In contrast, Q6.5SW activity in the SH remains generally weak during dust storms in other Martian years. Our analysis suggests that the unseasonal enhancement of Q6.5SWs is primarily driven by significant temperature increases associated with dust storms, while variations in zonal mean zonal wind may also play a secondary role in modulating wave amplitudes.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermosphere–Ionosphere Responses Over Thailand During the 2015 St. Patrick's Day Storm: Comparison of Observed O/N2 and VTEC With the SD WACCM-X Model Outputs","authors":"Paparin Jamlongkul,&nbsp;Suwicha Wannawichian,&nbsp;Larry J. Paxton,&nbsp;Clayton E. Cantrall,&nbsp;Han-Li Liu,&nbsp;Gang Lu,&nbsp;Pornchai Supnithi,&nbsp;Jirapoom Budtho","doi":"10.1029/2025JA033944","DOIUrl":"https://doi.org/10.1029/2025JA033944","url":null,"abstract":"<p>We present the first comparative analysis of observational data and model results focusing on thermospheric-ionospheric responses over the Thailand region by studying the St. Patrick's Day geomagnetic storm on 17–18 March, 2015. This study aims to advance our understanding of regional responses by building on previous observation-model comparisons. The observational data include global O/N₂ ratios from GUVI onboard the TIMED spacecraft, global vertical total electron content (VTEC) from the worldwide GNSS receivers obtained from the Madrigal database, and regional VTEC over Thailand from the KMI6 GNSS station. The atmospheric simulations used are from SD WACCM-X, incorporating high-latitude drivers from the Weimer and Assimilative Mapping of Ionospheric Electrodynamics (AMIE) models. The O/N₂ comparison focuses on TIMED's overpasses across Thailand at 3 UT (10 LT) on both days. Both models tend to reproduce general trends in the O/N₂ ratio and VTEC variations prior to the storm onset. The SD WACCM-X/Weimer model shows better agreement with the O/N₂ ratio from GUVI observations over Thailand, particularly during the recovery phase. Meanwhile, the SD WACCM-X/AMIE model better captures VTEC trends on both large and localized scales, especially after sunset, and successfully reproduces localized features over Thailand. However, during the early recovery phase, both Weimer and AMIE drivers fail to fully capture the collapse of the equatorial ionospheric anomaly (EIA) as indicated by VTEC data, likely due to overestimated <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>E</mi>\u0000 <mo>×</mo>\u0000 <mi>B</mi>\u0000 </mrow>\u0000 <annotation> $mathbf{E}times mathbf{B}$</annotation>\u0000 </semantics></math> drift values at low latitudes.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Statistical Modeling and Prediction of Ionospheric Equivalent Currents Based on SuperMAG Data","authors":"J. T. Manninen,&nbsp;H. Vanhamäki,&nbsp;A. T. Aikio,&nbsp;J. Gjerloev","doi":"10.1029/2025JA034125","DOIUrl":"https://doi.org/10.1029/2025JA034125","url":null,"abstract":"<p>We present a Solar Wind driven SuperMAG statistical Equivalent Current model (SW-SMEC), which represents the ionospheric equivalent currents in the Northern Hemisphere. The model is based on average current patterns derived from SuperMAG ground magnetometer data covering the solar cycle 23 (1997–2008). It predicts equivalent currents as function of the interplanetary magnetic field (IMF) clock angle, the solar wind electric field magnitude, and the Earth's dipole tilt. The equivalent currents predicted by our model show the well-known characteristics, such as strong dependence on the IMF north-south <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msub>\u0000 <mi>B</mi>\u0000 <mi>z</mi>\u0000 </msub>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({B}_{z}right)$</annotation>\u0000 </semantics></math> component and solar wind electric field. Positive IMF dawn-dusk <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msubsup>\u0000 <mi>B</mi>\u0000 <mi>y</mi>\u0000 <mo>+</mo>\u0000 </msubsup>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({B}_{y}^{+}right)$</annotation>\u0000 </semantics></math> component causes stronger equivalent currents than negative <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msubsup>\u0000 <mi>B</mi>\u0000 <mi>y</mi>\u0000 <mo>−</mo>\u0000 </msubsup>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({B}_{y}^{-}right)$</annotation>\u0000 </semantics></math> component. Equivalent currents are also stronger during summer than winter. The SW-SMEC model was tested in two case studies of geomagnetic storms, driven by a high-speed stream (HSS) and an interplanetary coronal mass ejection (ICME), respectively. The model succeeds in reproducing the main features of both HSS- and ICME-driven storms with comparable accuracy, as estimated by comparison with gridded SuperMAG data product. The accuracy is highest during the storm's main phase and lowest during the initial phase. A statistical study using 227 storms during the solar cycle 24 (2009–2019) shows that the model is more accurate with ICME-driven storms than with HSS-driven storms. It also shows that the optimal solar wind integration time for the model is typically 100 min, although it varies depending on the storm phase or driver.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034125","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366266","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Bow Shock Crossing Observations by MESSENGER From a Magnetic Point of View","authors":"K. Pump,&nbsp;D. Heyner,&nbsp;X. Blanco-Cano,&nbsp;D. Schmid,&nbsp;W. Sun,&nbsp;Y. Narita,&nbsp;F. Plaschke","doi":"10.1029/2025JA034009","DOIUrl":"https://doi.org/10.1029/2025JA034009","url":null,"abstract":"<p>Mercury possesses a weak internal magnetic field, which creates a magnetosphere and consequently a bow shock that interacts with the solar wind. Understanding the dynamics of the bow shock is essential for deepening our knowledge of Mercury's interaction with the solar wind. In this study, we address the challenge of identifying and classifying bow shock crossings using magnetic field data from the MESSENGER mission, collected from 2011 to 2015. We develop an automated detection method that categorizes crossings into three confidence levels. Our analysis reveals a total of 13,502 crossings, with 1,765 classified as very clear crossings (category 1), 5,027 indicated as clear crossings (category 2), and 6,710 as crossing detections of poor quality (category 3). We apply the method proposed by (Schmid &amp; Narita, 2023, https://doi.org/10.3847/1538-4357/aced07) to calculate the Alfvén Mach number based on the magnetic field jump characteristics. The shape and location of the bow shock are found to depend on upstream solar wind conditions, leading to a differentiation of crossings into quasi-parallel and quasi-perpendicular cases. We find that in the quasi-perpendicular case, the subsolar standoff distance decreases with increasing Alfvén Mach number, aligning with predictions from magnetohydrodynamic theory (Spreiter et al. (1966), https://doi.org/10.1016/0032-0633(66)90124-3; Chapman and Cairns (2003), https://doi.org/10.1029/2002ja009569). Conversely, no clear relationship is observed in the quasi-parallel case, likely due to complexities introduced by the foreshock region, which can alter the bow shock's structure. These findings illustrate the complex behavior of Mercury's bow shock and underscore the importance of further measurements, including plasma parameters, to improve our understanding of its dynamic interaction with the solar wind.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Azimuthal Asymmetry of Quasi-Zonally Propagating Medium-Scale Traveling Ionospheric Disturbances Revealed by the Low Latitude Long-Range Ionospheric Radar","authors":"Guofeng Dai,&nbsp;Guozhu Li,&nbsp;Lianhuan Hu,&nbsp;Wenjie Sun,&nbsp;Baiqi Ning,&nbsp;Yongqiang Hao,&nbsp;Donghe Zhang,&nbsp;Haiyong Xie,&nbsp;Xiukuan Zhao,&nbsp;Yi Li,&nbsp;Jianfei Liu","doi":"10.1029/2025JA034050","DOIUrl":"https://doi.org/10.1029/2025JA034050","url":null,"abstract":"<p>Using the Low-lAtitude long-Range Ionospheric raDar (LARID) at Hainan Island, we present a statistical survey of medium-scale traveling ionospheric disturbances (MSTIDs) at low latitudes in the East and Southeast Asia sector. MSTID signatures manifested as structured enhancements in the backscatter echo power maps, with dominant periods of 30–40 min and wavelengths of 150–250 km. The MSTIDs were observed to propagate quasi-zonally, with a higher occurrence rate in the quasi-eastward direction (74%) than in the quasi-westward direction (26%), a feature corroborated by nearby total electron content observations. The possible causes of the east-west asymmetry are discussed in terms of the geomagnetic activity, the atmospheric gravity wave (AGW) source and the neutral wind effects on the vertical propagation of AGW. We propose that the filtering effect of daytime westward thermospheric wind could contribute to the observed quasi-eastward propagation preference of MSTIDs. The propagation direction of quasi-zonally propagating MSTIDs in LARID and GNSS observations was slightly shifted poleward from the due zonal direction. The poleward shift could be contributed by the enhanced convection activities in the lower latitudes close to the equator, which could serve as an important source of AGWs.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"130 10","pages":""},"PeriodicalIF":2.9,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145366536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}