Journal of Geophysical Research: Space Physics最新文献

{"title":"Event Study of Cyclic Diffusion of the Proton Shell Distribution Associated With Quasi-Periodic Rising Tone Fast Magnetosonic Waves","authors":"Scott A. Boardsen,&nbsp;Lunjin Chen,&nbsp;Xueyi Wang,&nbsp;Goeff Reeves,&nbsp;František Němec,&nbsp;Huayue Chen","doi":"10.1029/2025JA034926","DOIUrl":"https://doi.org/10.1029/2025JA034926","url":null,"abstract":"<p>It has been proposed that the cyclic rising tone in frequency observed in rising tone quasi-periodic (QP) fast magnetosonic waves is due to the cyclic diffusion of the inner energy edge of the source proton shell distribution toward lower energies. Linear theory shows that as the inner edge of the proton shell diffuses inwards the unstable frequency rises leading to a rising tone. We present the first observations of this diffusion of the proton shell distribution for this type of wave event, observed by the HOPE instrument on Van Allen Probes B, where this diffusion is clearly observed in two back-to-back QP wave cycles. Linear instability is performed on the observed proton shell distribution, and the linear growth rate is compared with the observed wave frequency; the linear theory applied to the observed proton shell distributions was qualitatively but not quantitatively consistent with the observed wave frequencies. Nearby Waveform Receiver burst mode measurements showed that the spacing of the emission bands in frequency was very close to the proton cyclotron frequency <i>f</i>_<i>cP</i>, suggesting a near source. However, a ±2 nT spacecraft induced oscillation at ½ the spacecraft spin period in the background magnetic field magnitude could not allow us to conclude that the emission bands where at integer multiples of <i>f</i>_<i>cP</i>, a stronger condition for source proximity.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686759","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":"Quasi-Stationary Electron-Scale Current Sheet With Very Strong Electrostatic Field: Self-Consistent Structure and Electron Acceleration","authors":"M. V. Leonenko,&nbsp;E. E. Grigorenko,&nbsp;L. M. Zelenyi,&nbsp;H. S. Fu","doi":"10.1029/2025JA034895","DOIUrl":"https://doi.org/10.1029/2025JA034895","url":null,"abstract":"&lt;p&gt;We study a self-consistent configuration of the intense Electron-Scale Current Sheets (ECSs) under the presence of strong guide field &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mfenced&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;mi&gt;M&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mfenced&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $left({B}_{M}right)$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;. The ECSs were observed within the tailward Bursty Bulk Flow in the extremely hot PS. The purpose of our paper is twofold. First, we would like to determine mechanisms supporting the quasi-stationary ECS configuration, and, second, to investigate the possibility of additional electron acceleration by a strong ambipolar electric field, self-consistently arising in the quasi-stationary ECSs. We demonstrated that the intense ECSs (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;∼&lt;/mo&gt;\u0000 &lt;mn&gt;100&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${sim} 100$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; nA/&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msup&gt;\u0000 &lt;mi&gt;m&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{m}}^{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;) have 1D planar configuration self-consistently balanced by the central field-aligned current and perpendicular currents in its southern and northern edges. The field-aligned current is carried by the suprathermal high-speed electron beam, while the perpendicular currents are supported by electron diamagnetic and &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;E&lt;/mi&gt;\u0000 &lt;mo&gt;×&lt;/mo&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $mathbf{E}times mathbf{B}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; drifts due to the presence of the strong ambipolar electric field (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;∼&lt;/mo&gt;\u0000 &lt;mn&gt;50&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${sim} 50$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; mV/m). Electron anisotropy currents are negligible in this configuration. We found that the vertical pressure balance in the ECSs is mainly contributed not by the increase in guide magnetic field, but by the electron pressure enhancement. The strong ambipolar electric field related to the ECSs can accelerate field-aligned electron beams providing the energy gain up to &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;∼&lt;/mo&gt;\u0000 &lt;mn&gt;8&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${sim} 8$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; keV. This may lead to new ECSs formation ","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686745","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":"Ion-Neutral Coupling in the Southern Polar Cap by First Simultaneous Observations of Ion Drifts and Neutral Winds at Jang Bogo Station (JBS), Antarctica","authors":"Young-Bae Ham,&nbsp;Geonhwa Jee,&nbsp;Changsup Lee,&nbsp;Nikolay Zabotin,&nbsp;Hyuck-Jin Kwon,&nbsp;Eunsol Kim,&nbsp;Jeong-Han Kim,&nbsp;Qian Wu,&nbsp;Terence Bullett,&nbsp;Wenbin Wang","doi":"10.1029/2025JA034796","DOIUrl":"https://doi.org/10.1029/2025JA034796","url":null,"abstract":"<p>Simultaneous observations of ion drifts and neutral winds have been conducted at Jang Bogo Station (JBS), Antarctica since 2017 using a Dynasonde and a Fabry-Perot Interferometer, respectively. This study presents the results of a comparison between these two measurements to investigate the impacts of ion drifts on neutral winds in the Southern polar cap during winter. The results observationally demonstrate that neutral winds are largely weaker than ion drifts, suggesting that the neutral winds rarely reach a statistical steady-state. However, thermosphere-ionosphere-electrodynamics general circulation model simulations show the opposite trend, significantly underestimating ion drifts. Neutral winds are also found to have different characteristics depending on the magnetic local time sectors, being weaker on the dayside than on the nightside of the polar cap, which is possibly explained if the previous histories of the neutrals before being observed are considered. Additionally, changes in neutral winds due to ion drag are more noticeable in the duskside than in the dawnside due to differences in collision frequency, which is primarily dependent on the diurnal variations of ionospheric density at JBS.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686831","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":"Juno Witnesses Extreme Compression of Jupiter's Magnetosphere","authors":"R. J. Wilson,&nbsp;F. Bagenal,&nbsp;M. J. Brennan,&nbsp;J. E. P. Connerney,&nbsp;S. Eriksson,&nbsp;R. S. Giles,&nbsp;T. K. Greathouse,&nbsp;W. S. Kurth,&nbsp;C. P. Paranicas,&nbsp;R. Ramstad,&nbsp;M. J. Rutala,&nbsp;M. F. Vogt,&nbsp;G. J. Fuller,&nbsp;F. Allegrini,&nbsp;R. W. Ebert","doi":"10.1029/2025JA034955","DOIUrl":"https://doi.org/10.1029/2025JA034955","url":null,"abstract":"<p>In October 2024, the Juno spacecraft observed an extreme compression of Jupiter's magnetosphere. This event pushed the magnetosheath into an unprecedented distance of only 30 Jupiter radii from Jupiter. This suggests an enhanced Solar Wind (SW) dynamic pressure (DynP), that was likely produced from a coronal mass ejection after an X1.8 class solar flare. The compression brought the magnetosheath, observed at a high southern latitude, to the closest distance ever observed from Jupiter. Using data from multiple instruments on Juno to identify magnetosheath signatures, it is shown that Juno had many encounters with the magnetosheath as it moved inward from apojove to perijove. This included many short-lived encounters that were not readily identifiable from a single data set. From model estimates, a SW DynP of around 1.2 <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>n</mi>\u0000 <mi>P</mi>\u0000 <mi>a</mi>\u0000 </mrow>\u0000 <annotation> $nPa$</annotation>\u0000 </semantics></math> is suggested for this event, consistent with previous upper estimates observed in the vicinity of Jupiter's orbital path. Remote imaging suggests the magnetosphere remained compressed for several days after this event. The event raises the possibility that Jupiter's magnetosphere on the dayside could potentially shrink inside of Callisto's orbital path, and that if Callisto happened to be on the dayside of Jupiter at the time (although it was on the nightside during this event), it could find itself outside of the jovian magnetosphere and exposed directly to the SW.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686722","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":"Coupling Between Sudden Stratospheric Warming and Mid-Latitude Ionosphere of European Sector - A Case Study","authors":"S. K. Ramatheerthan,&nbsp;M. Kozubek,&nbsp;J. Laštovička,&nbsp;Z. Mošna,&nbsp;P. Koucká Knížová,&nbsp;J. Urbář","doi":"10.1029/2025JA034183","DOIUrl":"https://doi.org/10.1029/2025JA034183","url":null,"abstract":"<p>The 10 hPa level is conventionally used for determining sudden stratospheric warming in studies. Our study examines the winter of 2005–2006 from 1 to 10 hPa pressure levels, identifying three significant warming episodes in January 2006 instead of only one based on the 10 hPa level definition. The first two episodes with temperature peaks occurring around 3 and 10 January, respectively, are identified at the upper stratosphere, where they are stronger than the official warming peak on 22 January defined at 10 hPa. Increased wave activity at these upper levels, derived from the Eliassen-Palm flux divergence, highlights the intensity of warming and circulation changes at the upper stratospheric layers. Ionospheric analysis of January 2006 revealed substantial impacts on the F2 layer ionosphere, particularly in Juliusruh. These effects are linked to planetary wave periodicities detected in wavelet spectrum analysis. These periodicities are noted in the temperature and wind, predominantly in the upper stratosphere. Further analysis employs a wavelet coherence between the upper stratosphere and the critical frequency of the F2 layer that affirms that the planetary-scale periodicities observed in the upper stratosphere are mirrored in the F2 layer mid-latitude ionosphere over station Juliusruh. These findings suggest a relationship between the upper stratosphere and the ionosphere, particularly at stations near the climatological vortex edge around 60°N. The novelty of this paper is that for studying the impact of sudden stratospheric warmings on the mid-latitude ionosphere, it is better to use the major SSW definition at upper stratospheric levels rather than the traditional 10 hPa level.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686741","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":"Magnetosphere–Ionosphere Coupling Driven by Solar Wind Density Pulse Under Northward IMF Bz: Role of IMF By","authors":"Sirsha Nandy,&nbsp;Bhargav Vaidya,&nbsp;Arghyadeep Paul,&nbsp;Diptiranjan Rout,&nbsp;Dibyendu Chakrabarty,&nbsp;Antoine Strugarek","doi":"10.1029/2025JA034845","DOIUrl":"https://doi.org/10.1029/2025JA034845","url":null,"abstract":"&lt;p&gt;Perturbations in the solar wind caused by space weather drivers can have a significant impact on the magnetosphere and subsequently on the ionosphere, producing global geomagnetic effects. Understanding and characterizing these responses requires a detailed study of magnetosphere–ionosphere (MI) coupling under varying space weather forcing conditions. In this study, we present global 3D magnetohydrodynamic (MHD) simulations with a two-way coupled MI coupling module to study the impact of a solar wind density pulse on the spatial and temporal profiles of ionospheric field-aligned currents (FACs) under northward interplanetary magnetic field (IMF) conditions. The pulse compresses and relaxes the magnetosphere, generating Alfvénic disturbances that manifest as alternating polarity FACs on the ionosphere. We find that the MI response is also significantly modulated by the IMF clock angle. For small, non-zero IMF &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;mi&gt;y&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mo&gt;±&lt;/mo&gt;\u0000 &lt;mn&gt;2.5&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${B}_{y}=pm 2.5$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; nT, FAC profiles show the largest enhancement and enable prompt penetration electric fields (PPEF). The IMF &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;mi&gt;y&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;0&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${B}_{y}=0$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; case shows weaker, symmetric enhancements, while a higher IMF &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;mi&gt;y&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;5&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${B}_{y}=5$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; nT creates a dominant convection cell that suppresses oscillatory currents, yielding diffuse and delayed responses. FACs intensify rapidly within &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;∼&lt;/mo&gt;\u0000 &lt;mn&gt;10&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${sim} 10$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; min after impact, consistent with Alfvén wave travel time from magnetosphere to ionosphere. We compare our model results with relevant observations from AMPERE, which exhibit similar ","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686804","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":"Juno Observations of Large-Scale Azimuthal Fields and Flows in Jupiter's Nightside Magnetosphere: Field-Aligned Currents, Effective Ionospheric Pedersen Conductivity, and Power to Atmospheric Heating","authors":"G. Provan,&nbsp;S. W. H. Cowley,&nbsp;J. D. Nichols,&nbsp;J.-Z. Wang,&nbsp;R. J. Wilson","doi":"10.1029/2025JA034937","DOIUrl":"https://doi.org/10.1029/2025JA034937","url":null,"abstract":"<p>Using the methodology of Cowley et al. (https://doi.org/10.1029/2025JA033993), we employ ∼8 years of Juno azimuthal magnetic field data to derive colatitude profiles of Jupiter's nightside (17-05 hr via midnight) ionospheric equatorward Pedersen current from near the magnetic pole to inner magnetosphere field lines at 18° colatitude, from which we quantify large-scale field-aligned currents on spatial scales ∼1°. Polar-tail Pedersen currents are ∼1–2 MA per radian of azimuth, with regions of downward and upward currents of order tens nA m⁻². Stronger downward currents ∼50–200 nA m⁻² flow in an outer magnetosphere layer that is wider at dusk (∼7°) than at dawn (∼2°), with peak Pedersen currents near the outer/middle magnetosphere boundary reaching ∼12 MA rad⁻¹ at dusk falling to ∼2.5 MA rad⁻¹ at dawn. Upward currents of order hundreds of nA m⁻² flow on middle magnetosphere field lines across which the Pedersen current falls to small values. The Pedersen currents are also combined with Juno/JADE-I plasma angular velocity measurements to determine Jupiter's effective ionospheric height-integrated Pedersen conductivity, together with the power input to thermospheric heating. Outer magnetosphere effective conductivities are ∼0.4 mho at dusk, falling to ∼0.25 mho at midnight, and ∼0.1 mho pre-dawn. No significant increase in conductivity is found in the middle magnetosphere region of strong upward current, suggesting that thermospheric winds closely track the plasma velocity in this region. Latitude-integrated powers show a similar dusk-dawn asymmetry, with a total nightside power per hemisphere of ∼370 TW, of which ∼55% is input to thermospheric heating and 45% to the magnetospheric plasma.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034937","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686353","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":"Imprint of the Quasi-Biennial Oscillation on the Ionosphere and Thermosphere","authors":"D. Singh,&nbsp;L. P. Goncharenko,&nbsp;S. R. Zhang","doi":"10.1029/2025JA034748","DOIUrl":"https://doi.org/10.1029/2025JA034748","url":null,"abstract":"<p>The Quasi-Biennial Oscillation (QBO) is a dominant mode of stratospheric variability and is known to modulate the variability of the ionosphere-thermosphere (IT) system. However, the extent of its influence on the ionosphere-thermosphere system remains uncertain due to weak signals and confounding with similar periodicities in solar flux. In this study, we investigated QBO signatures in ionosonde derived peak electron density (NmF2), GNSS total electron content (TEC), and thermospheric composition (<i>O</i>/<i>N</i>₂) from the Global Ultraviolet Imager on NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. Local empirical models are used to isolate the stratospheric QBO signature in NmF2 and TEC. Multi-channel singular spectrum analysis is used to reveal seasonal modulation of the <i>O/N</i>_<i>2</i> response to QBO. We found that the amplitude of non-solar origin QBO in NmF2, TEC, and <i>O/N</i>_<i>2</i> reaches up to 4% and exhibits an out-of-phase relation with stratospheric QBO phase at 30 hPa (QBO30). The TEC QBO signal shows strong regional variability, peaking over Europe. The <i>O/N</i>_<i>2</i> QBO signal shows clear seasonality with maximum correlation with QBO30 around the equinoxes. The NmF2 response to stratospheric QBO is enhanced at most stations during the September equinox. The QBO signal in <i>O</i>/<i>N</i>₂ at different latitudes shows maximum correlation with the stratospheric QBO at different pressure levels. Overall, the global reduction in NmF2, TEC, and <i>O</i>/<i>N</i>₂ during the eastward QBO phase, along with their seasonal structure, is consistent with enhanced mixing driven by migrating diurnal tide. However, the regional structure in the TEC response implies additional mechanisms with varying spatial influence and vertical extent.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034748","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686905","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":"Comprehensive Characterization of Water Group Ion Composition and Distributions in Saturn's Magnetosphere With Cassini Plasma Spectrometer Data","authors":"Thomas K. Kim,&nbsp;D. B. Reisenfeld,&nbsp;R. J. Wilson,&nbsp;H. T. Smith,&nbsp;A. K. Woodson,&nbsp;F. Allegrini,&nbsp;R. W. Ebert,&nbsp;M. G. Henderson,&nbsp;P. K. Kollmann,&nbsp;G. Livadiotis,&nbsp;G. Nicolaou,&nbsp;J. R. Szalay,&nbsp;P. W. Valek,&nbsp;A. Masters","doi":"10.1029/2025JA034738","DOIUrl":"https://doi.org/10.1029/2025JA034738","url":null,"abstract":"<p>Saturn's magnetosphere is continuously supplied with neutrals from the Enceladus plume and the icy rings, which undergo ionization and charge-exchange to form a complex water-group plasma environment. While the Cassini Plasma Spectrometer (CAPS) instrument has provided extensive compositional information, detailed separation of individual water-group ion species in time-of-flight (TOF) data has not previously been achieved. In this study, we perform forward modeling of CAPS-IMS energy-per-charge (E/Q) and TOF spectra obtained between 2004 and 2012 to resolve O⁺, OH⁺, H₂O⁺, and H₃O⁺ and to characterize their plasma properties, including number density, temperature, and thermodynamic κ. Our results demonstrate that O⁺ is the dominant thermal ion species throughout Saturn's magnetosphere, comprising up to ∼70% of the total ion population beyond ∼5 Saturn radii (R_S). In contrast, molecular ions such as OH⁺, H₂O⁺, and H₃O⁺ dominate closer to Enceladus but rapidly dissociate into atomic ions between ∼5 and 10 R_S. This radial region is also characterized by the steepest increase in plasma flow speed, which rises from ∼40% to ∼80% of rigid corotation. Simultaneously, ion velocity distributions approach Maxwell–Boltzmann equilibrium, as indicated by high kappa values. These findings provide new constraints on the ion–neutral chemistry that regulates the balance between molecular and atomic ions in Saturn's magnetosphere. They also emphasize the critical role of the 5–10 R_S region as a transition zone for both plasma composition and dynamics. Our results refine previous CAPS-based studies and underscore the need to incorporate seasonal variability and ionospheric coupling into future global models of Saturn's plasma environment.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034738","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147686904","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":"ULF Wave Modulation of Energetic Electron Precipitation Caused by the Self-Limiting of Space Radiation: May 2024 Superstorm Observations","authors":"L. Olifer,&nbsp;D. Zhou,&nbsp;M. Patel,&nbsp;I. R. Mann,&nbsp;M. K. Hudson,&nbsp;A. W. Degeling,&nbsp;C. O. Heinke,&nbsp;G. R. Sivakoff,&nbsp;A. Kale,&nbsp;S. Kasahara,&nbsp;S. Yokota,&nbsp;K. Keika,&nbsp;T. Hori,&nbsp;T. Mitani,&nbsp;T. Takashima,&nbsp;Y. Kasahara,&nbsp;S. Matsuda,&nbsp;A. Shinbori,&nbsp;A. Matsuoka,&nbsp;M. Teramoto,&nbsp;K. Yamamoto,&nbsp;I. Shinohara,&nbsp;Y. Miyoshi","doi":"10.1029/2025JA034908","DOIUrl":"https://doi.org/10.1029/2025JA034908","url":null,"abstract":"<p>The May 2024 geomagnetic superstorm provided the opportunity to explore how strong wave-particle interactions affect energetic electron precipitation under intense driving. Using coordinated measurements from a balloon-borne Timepix-based X-ray detector, ground-based riometers and magnetometers, and Arase satellite observations, we identified quasi-periodic bursts of energetic electron precipitation coincident with Pc5 ultra low frequency (ULF) wave oscillations. Arase satellite data revealed energy-dispersed trapped energetic electron flux modulations in the “seed” energy range, indicating that trapped electron flux was likely modulated by ULF waves. This letter reveals that these flux enhancements surpassed the Kennel-Petschek (K-P) limit, creating intense chorus waves and driving periodic electron precipitation. Drift-dispersion analysis traced these modulations back to a source in the post-noon magnetospheric sector, matching balloon and ground-based measurements. Here, we propose a novel indirect ULF wave-driven mechanism for modulated energetic electron precipitation, whereby periodic modulations of “seed” electron fluxes enhance electron losses.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"131 4","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JA034908","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147666274","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}