Journal of Geophysical Research: Space Physics最新文献

{"title":"The Evolution of Earth's Outer Radiation Belt Over Geomagnetic Storm Phase in Van Allen Probe Era","authors":"Xu Wang, Lei Dai, Ren Yong, Senlin Xiong, Chi Wang","doi":"10.1029/2024JA032674","DOIUrl":"https://doi.org/10.1029/2024JA032674","url":null,"abstract":"<p>Earth's outer radiation belts are highly dynamic during geomagnetic storms. Using electron flux data from 226 keV to 2.6 MeV measured by the Van Allen Probes, we statistically analyzed the peak flux position <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>peak</mi>\u0000 </msub>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({L}_{mathit{peak}}right)$</annotation>\u0000 </semantics></math> and inner boundary position <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mfenced>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>min</mi>\u0000 </msub>\u0000 </mfenced>\u0000 </mrow>\u0000 <annotation> $left({L}_{min }right)$</annotation>\u0000 </semantics></math> of the outer radiation belt across different storm phases: pre-storm quiet time, main phase, early recovery phase, and later recovery phase. This analysis covered 196 geomagnetic storm events from October 2012 to September 2019. Our results indicate that: (a) During the pre-storm, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>peak</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${L}_{mathit{peak}}$</annotation>\u0000 </semantics></math> decreases with increasing energy. From the pre-storm to the early recovery phase, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>peak</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${L}_{mathit{peak}}$</annotation>\u0000 </semantics></math> shifts inward for energies below 1 MeV and outward for energies above 1 MeV. For all energies, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>peak</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${L}_{mathit{peak}}$</annotation>\u0000 </semantics></math> converges to approximately L = <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>∼</mo>\u0000 </mrow>\u0000 <annotation> ${sim} $</annotation>\u0000 </semantics></math>4.3–4.6 in the early recovery phase. (b) Below approximately 1 MeV, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>L</mi>\u0000 <mi>min</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${L}_{min }$</annotation>\u0000 </semantics></math> generally move inward from the main phase to the early r","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541083","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":"Measurement of the Taylor Microscale and the Effective Magnetic Reynolds Number in the Solar Wind With Cluster","authors":"O. W. Roberts,&nbsp;K. G. Klein,&nbsp;Z. Vörös,&nbsp;R. Nakamura,&nbsp;X. Li,&nbsp;Y. Narita,&nbsp;D. Schmid,&nbsp;R. Bandyopadhyay,&nbsp;W. H. Matthaeus","doi":"10.1029/2024JA032968","DOIUrl":"https://doi.org/10.1029/2024JA032968","url":null,"abstract":"<p>We use magnetic field data from the Cluster mission to estimate the value of the Taylor microscale and the effective magnetic Reynolds number in the interplanetary solar wind. Turbulent cascades can be characterized by the spatial scale at which dissipation begins to impact the local energy transfer, estimated by the Taylor microscale, as well as the separation between the injection and dissipation scales, estimated by the effective magnetic Reynolds number. Estimating the Taylor microscale requires measurements of the autocorrelation function at small separations. The Cluster spacecraft have exceptionally sensitive search coil magnetometers with high time resolution, making them ideal for measuring the Taylor microscale. We obtain a value of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>430</mn>\u0000 <mo>±</mo>\u0000 <mn>20</mn>\u0000 </mrow>\u0000 <annotation> $430pm 20$</annotation>\u0000 </semantics></math> km; smaller than most previous measurements. We interpret this value as being smaller due to the higher time resolution, enabling the curvature of the autocorrelation function to be measured closer to the origin, giving a more accurate measurement. Combining the Taylor Microscale's computed value with concurrent correlation length measurements, we obtain a value of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>150</mn>\u0000 <mo>,</mo>\u0000 <mn>000</mn>\u0000 <mo>±</mo>\u0000 <mn>10</mn>\u0000 <mo>,</mo>\u0000 <mn>000</mn>\u0000 </mrow>\u0000 <annotation> $150,000pm 10,000$</annotation>\u0000 </semantics></math> for the effective magnetic Reynolds number, which compares well to other observations. The four spacecraft of Cluster also allow directions transverse to the flow to be surveyed. The small separations (7 km) of Clusters 3 and 4 show that the Taylor microscale may vary as a function of direction to the mean magnetic field direction. The observed differences are small, requiring more observations to confirm this anisotropy.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032968","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541015","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":"Deriving the Ionospheric Electric Field From the Bulk Motion of Radar Aurora in the E-Region","authors":"Magnus F. Ivarsen,&nbsp;Jean-Pierre St-Maurice,&nbsp;Devin R. Huyghebaert,&nbsp;Megan D. Gillies,&nbsp;Frank Lind,&nbsp;Brian Pitzel,&nbsp;Glenn C. Hussey","doi":"10.1029/2024JA033060","DOIUrl":"https://doi.org/10.1029/2024JA033060","url":null,"abstract":"<p>In the auroral E-region strong electric fields can create an environment characterized by fast plasma drifts. These fields lead to strong Hall currents which trigger small-scale plasma instabilities that evolve into turbulence. Radio waves transmitted by radars are scattered off of this turbulence, giving rise to the ‘radar aurora’. However, the Doppler shift from the scattered signal does not describe the F-region plasma flow, the <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 imposed by the magnetosphere. Instead, the radar aurora Doppler shift is typically limited by nonlinear processes to not exceed the local ion-acoustic speed of the E-region. This being stated, recent advances in radar interferometry enable the tracking of the <i>bulk motion</i> of the radar aurora, which can be quite different and is typically larger than the motion inferred from the Doppler shift retrieved from turbulence scatter. We argue that the bulk motion inferred from the radar aurora tracks the motion of turbulent source regions (provided by auroras). This allows us to retrieve the electric field responsible for the motion of field tubes involved in auroral particle precipitation, since the precipitating electrons must <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. Through a number of case studies, as well as a statistical analysis, we demonstrate that, as a result, the radar aurora <i>bulk motion</i> is closely associated with the high-latitude convection electric field. We conclude that, while still in need of further refinement, the method of tracking structures in the radar aurora has the potential to provide reliable estimates of the ionospheric electric field that are consistent with nature.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA033060","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541078","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":"Detection of Extensive Equatorial Plasma Depletions After the 2022 Tongan Volcanic Eruption From Multiple Geodetic Satellite Ranging Systems","authors":"Shin-Chan Han,&nbsp;Hyosub Kil,&nbsp;Richard Ray,&nbsp;Frank Lemoine,&nbsp;Colin Waters","doi":"10.1029/2024JA032690","DOIUrl":"https://doi.org/10.1029/2024JA032690","url":null,"abstract":"<p>We present a number of unique observations of ionospheric anomalies following the Hunga-Tonga Hunga-Ha'apai (HTHH) volcanic eruption on 15 January 2022. All are based on non-dedicated geodetic satellite systems: Global Positioning System tracking of Low Earth Orbit (LEO) CubeSats, intersatellite tracking between two GRACE Follow-On satellites, satellite radar altimeters to the ocean surface, and Doppler radio beacons from ground stations to LEO geodetic satellites. Their observations revealed the development of anomalously large trough-like plasma depletions, along with plasma bubbles, in the equatorial regions of the Pacific and East Asian sectors. Trough-like plasma depletions appeared to be confined within approximately ±20° magnetic latitude, accompanied by density enhancements just outside this latitude range. These plasma depletions and enhancements were aligned with the magnetic equator and occurred across broad longitudes. They were detected in regions where atmospheric waves from the HTHH eruption passed through around the time of the sunset terminator. We interpret these phenomena in terms of the <i>E</i> dynamo electric fields driven by atmospheric waves from the eruption. The uplift of the ionosphere beyond satellite altitudes, followed by subsequent plasma diffusion to higher latitudes along magnetic field lines, results in the formation of trough-like plasma depletions around the magnetic equator and density enhancement at higher latitudes. The detection of plasma bubbles in the Asian sector during the non-bubble season (January) is likely associated with the uplift of the ionosphere at the sunset terminator.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541018","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":"Revisiting the Superstorm on 6–7 April 2000 Caused by an Extraordinary Corotating Interaction Region (With an Embedded Coronal Jet?)","authors":"Bruce T. Tsurutani,&nbsp;Rajkumar Hajra,&nbsp;Gurbax Lakhina,&nbsp;Xing Meng","doi":"10.1029/2024JA032989","DOIUrl":"https://doi.org/10.1029/2024JA032989","url":null,"abstract":"<p>The 6–7 April 2000 superstorm of SYM-H intensity = −319 nT discussed in Meng et al. (2019; https://doi.org/10.1029/2018JA026425) was misidentified as being due to an interplanetary coronal mass ejection associated with a solar flare. The interplanetary cause was a highly unusual corotating interaction region (CIR) bounded by a strong fast forward shock (FS) with magnetosonic Mach number <i>M</i>_ms = 4.6 and a fast reverse shock (RS) with <i>M</i>_ms = 1.9. The exceptionally strong FS caused a ∼3-factor interplanetary magnetic field (IMF) magnitude amplification in the leading half of the CIR with peak southward IMF <i>B</i>_z = −27 nT causing the superstorm. A plasma region between a tangential discontinuity and the stream interface had a scale size of ∼0.096 AU. We hypothesize that this is the first detection of a coronal jet at 1 AU. The jet/Gold magnetic tongue (1959; https://doi.org/10.1029/JZ064i011p01665) was embedded within the CIR, contained the southward <i>B</i>_z and caused the magnetic storm. We hypothesize that a shrinking coronal hole and magnetic reconnection caused the formation and release of the jet.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541077","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":"ELFIN-GPS Comparison of Energetic Electron Fluxes: Modeling Low-Altitude Electron Flux Mapping to the Equatorial Magnetosphere","authors":"Weiqin Sun,&nbsp;Xiao-Jia Zhang,&nbsp;Anton V. Artemyev,&nbsp;Didier Mourenas,&nbsp;Steven K. Morley,&nbsp;Vassilis Angelopoulos,&nbsp;S. Kasahara,&nbsp;Y. Miyoshi,&nbsp;A. Matsuoka,&nbsp;T. Mitani,&nbsp;S. Yokota,&nbsp;T. Hori,&nbsp;K. Keika,&nbsp;T. Takashima,&nbsp;M. Teramoto,&nbsp;I. Shinohara,&nbsp;K. Yamamoto","doi":"10.1029/2024JA033155","DOIUrl":"https://doi.org/10.1029/2024JA033155","url":null,"abstract":"<p>Near-equatorial measurements of energetic electron fluxes, in combination with numerical simulation, are widely used for monitoring of the radiation belt dynamics. However, the long orbital periods of near-equatorial spacecraft constrain the cadence of observations to once per several hours or greater, that is, much longer than the mesoscale injections and rapid local acceleration and losses of energetic electrons of interest. An alternative approach for radiation belt monitoring is to use measurements of low-altitude spacecraft, which cover, once per hour or faster, the latitudinal range of the entire radiation belt within a few minutes. Such an approach requires, however, a procedure for mapping the flux from low equatorial pitch angles (near the loss cone) as measured at low altitude, to high equatorial pitch angles (far from the loss cone), as necessitated by equatorial flux models. Here we do this using the high energy resolution ELFIN measurements of energetic electrons. Combining those with GPS measurements we develop a model for the electron anisotropy coefficient, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>n</mi>\u0000 </mrow>\u0000 <annotation> $n$</annotation>\u0000 </semantics></math>, that describes electron flux <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>j</mi>\u0000 <mi>trap</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${j}_{mathit{trap}}$</annotation>\u0000 </semantics></math> dependence on equatorial pitch-angle, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>α</mi>\u0000 <mrow>\u0000 <mi>e</mi>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${alpha }_{eq}$</annotation>\u0000 </semantics></math>, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>j</mi>\u0000 <mi>trap</mi>\u0000 </msub>\u0000 <mo>∼</mo>\u0000 <msup>\u0000 <mi>sin</mi>\u0000 <mi>n</mi>\u0000 </msup>\u0000 <msub>\u0000 <mi>α</mi>\u0000 <mrow>\u0000 <mi>e</mi>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${j}_{mathit{trap}}sim {sin }^{n}{alpha }_{eq}$</annotation>\u0000 </semantics></math>. We then validate this model by comparing its equatorial predictions from ELFIN with in-situ near-equatorial measurements from Arase (ERG) in the outer radiation belt.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 11","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142541017","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":"Observations of Significant Ion Energy Outflows Associated With Cusp Ion Outflows and the Role of Poynting Flux as an Energy Source","authors":"S. Tian,&nbsp;J. R. Wygant,&nbsp;C. A. Cattell,&nbsp;J. P. Dombeck,&nbsp;J. Bortnik","doi":"10.1029/2024JA032644","DOIUrl":"https://doi.org/10.1029/2024JA032644","url":null,"abstract":"<p>The cusp ion outflow on Earth has been extensively studied for decades. However, the energy flux associated with the ion outflow, which is of equivalent importance to the number flux or mass flux, has been rarely studied. Here, we present the first systematic study on the cusp ion energy flux and the energy budget along the cusp magnetic flux tube using quasi-conjunction observations from the Polar and Fast satellites. Significant ion energy fluxes (several 10s mW/<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mrow>\u0000 <msup>\u0000 <mi>m</mi>\u0000 <mn>2</mn>\u0000 </msup>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> ${mathrm{m}}^{2}$</annotation>\u0000 </semantics></math> mapped to 100 km altitude) away from the Earth are frequently observed in the mid-altitude cusp (3–6 Re). Observations at low altitudes (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mrow>\u0000 <mo>&lt;</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> ${&lt; } $</annotation>\u0000 </semantics></math>2 Re) show that the upward ion energy flux is associated with ion outflows originating from the ionosphere. In addition, we show that the ion outflows experience intense energization well above the ionosphere. The only possible energy source for this energization is the earthward Poynting flux in mid-altitude. The electrons are accelerated downward and are another energy sink (not source). The altitude profile of the energy fluxes suggests a transition region between 2 and 4 Re where both ion heating and electron acceleration primarily occur and where significant Poynting flux is dissipated. Analysis of the E/B ratio shows that the Poynting flux is carried by both the Alfven waves and quasi-static structures. The above results place important constraints on possible local ion energization mechanisms.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 10","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525457","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":"Formation of Standing Whistler Wave in Earth's Magnetosheath","authors":"Yang Wang,&nbsp;Jun Zhong,&nbsp;Lou-Chuang Lee,&nbsp;Jiansen He,&nbsp;Hui Zhang,&nbsp;Zhaojin Rong,&nbsp;Yong Wei","doi":"10.1029/2024JA033358","DOIUrl":"https://doi.org/10.1029/2024JA033358","url":null,"abstract":"<p>The dispersion of shock is universal in various media, and in plasmas, standing whistler waves represent the dispersion of collisionless shocks. These standing whistler waves are usually observed upstream of low Mach number planetary bow shocks and interplanetary shocks. However, our understanding of the plasma behavior and electric field properties within these waves remains limited. Using conjoint THEMIS and Magnetospheric Multiscale (MMS) observations, we report the first observation of standing whistler wave upstream of a fast shock in Earth's magnetosheath resulting from the interaction between a solar wind tangential discontinuity and the bow shock. High-resolution MMS measurements provide unprecedented insights into these waves, characterizing their circular polarization, near-parallel propagation to the shock normal, and fixed phase relative to the shock ramp. The observed field and particle characteristics are discussed in detail.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 10","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA033358","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525567","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 Activity Dependence of Traveling Ionospheric Disturbance Amplitudes Using a Rapid-Run Ionosonde in High Latitudes","authors":"Samson T. Moges,&nbsp;Alexander Kozlovsky,&nbsp;Ruslan O. Sherstyukov,&nbsp;Thomas Ulich","doi":"10.1029/2024JA033013","DOIUrl":"https://doi.org/10.1029/2024JA033013","url":null,"abstract":"<p>We investigated the amplitude of medium scale traveling ionospheric disturbances (MSTIDs, with periods 25–100 min) and their dependence on the solar activity using 16 years data of the rapid run-ionosonde operating at high latitudes (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>67</mn>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <annotation> $67{}^{circ}$</annotation>\u0000 </semantics></math>N, Sodankylä, Finland). A deep learning neural network was applied to ionograms to extract critical frequency of the F2 region (foF2) with a 1 min time resolution. Then, we analyzed the relative amplitude of MSTIDs (i.e., <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>2</mn>\u0000 <mi>δ</mi>\u0000 </mrow>\u0000 <annotation> $2delta $</annotation>\u0000 </semantics></math>foF2/foF2), which corresponds to the amplitude of atmospheric gravity waves (AGWs) causing MSTIDs. The amplitude of AGWs propagating upward increases with height due to the decreasing density of the air, and hmF2 varies depending on local time, seasonal and solar activity conditions. To account for this effect, we calculated a corrected MSTID amplitude by normalizing the relative amplitude for the air density at the hmF2. The corrected amplitudes show no clear dependence on F10.7 during winter (0–12 UT), equinox (20-01 UT) and summer (19-01 UT), while a positive dependence of corrected amplitudes on F10.7 was observed during winter and equinox, in 14–22 UT and 15–19 UT, respectively. Corresponding to the dependence behaviors of corrected and relative amplitudes, two likely mechanisms of MSTIDs, AGWs from the lower atmosphere and auroral sources, are inferred. Their subsequent roles in the solar activity dependence of MSTID amplitudes were separately discussed, although in reality, the observed dependence is complex and often involves several mechanisms together.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 10","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA033013","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525565","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":"Classifying Magnetic Reconnection Regions Using k-Means Clustering: Applications to Energy Partition","authors":"Cara L. Waters,&nbsp;Jonathan P. Eastwood,&nbsp;Naïs Fargette,&nbsp;David L. Newman,&nbsp;Martin V. Goldman","doi":"10.1029/2024JA033010","DOIUrl":"https://doi.org/10.1029/2024JA033010","url":null,"abstract":"<p>Magnetic reconnection is a fundamental plasma process which facilitates the conversion of magnetic energy to particle energies. This local process both contributes to and is affected by a larger system, being dependent on plasma conditions and transporting energy around the system, such as Earth's magnetosphere. When studying the reconnection process with in situ spacecraft data, it can be difficult to determine where spacecraft are in relation to the reconnection structure. In this work, we use <i>k</i>-means clustering, an unsupervised machine learning technique, to identify regions in a 2.5-D PIC simulation of symmetric magnetic reconnection with conditions comparable to those observed in Earth's magnetotail. This allows energy flux densities to be attributed to these regions. The ion enthalpy flux density is the most dominant form of energy flux density in the outflows, agreeing with previous studies. Poynting flux density may be dominant at some points in the outflows and is only half that of the Poynting flux density in the separatrices. The proportion of outflowing particle energy flux decreases as guide field increases. We find that <i>k</i>-means is beneficial for analyzing data and comparing between simulations and in situ data. This demonstrates an approach which may be applied to large volumes of data to determine statistically different regions within phenomena in simulations and could be extended to in situ observations, applicable to future multi-point missions.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 10","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA033010","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525566","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}