Journal of Geophysical Research: Space Physics最新文献

{"title":"Ion Diffusive Transport Across the Separatrix Between the Low-Latitude Mantle and the Plasma Sheet by Kinetic Alfvén Waves: MMS Observation","authors":"Chih-Ping Wang,&nbsp;Jay R. Johnson,&nbsp;Xiaoyan Xing,&nbsp;Levon A. Avanov,&nbsp;H. Y. Wei,&nbsp;Narges Ahmadi","doi":"10.1029/2024JA032719","DOIUrl":"https://doi.org/10.1029/2024JA032719","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>To understand the entry of the cool low-latitude mantle ions into the tail plasma sheet near the flanks under persistent interplanetary magnetic field B_y, we evaluate the role of the cross-field diffusive transport by kinetic Alfvén waves (KAWs) by investigating two events observed by multiscale (MMS) spacecraft. Around the separatrix between the open and closed field-line regions, a two-component mixing of hot plasma sheet ions of a few keV with cool mantle ions of a few hundred eV was observed, indicating transport across the separatrix. The waves observed between 0.01 and 10 Hz around the separatrix had characteristics consistent with those of KAWs. The consistency allowed us to estimate the wave vectors as a function of frequency by fitting KAW dispersion to the observations. Using the observed wave powers, plasma moments, and the estimated wave vectors, we computed the cross-field diffusion rates associated with KAWs. The diffusion rates were found to be comparable to or larger than the Bohm diffusion rates during the intervals when the two-component mixing was observed, indicating that the KAW diffusive transport can play a role in the entry of low-latitude mantle ions into the plasma sheet.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142451255","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":"Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He+ Band EMIC Waves","authors":"Su Zhou,&nbsp;Yongzhi Cai","doi":"10.1029/2024JA032954","DOIUrl":"https://doi.org/10.1029/2024JA032954","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>The energy of ring current protons is believed to influence the pitch angle scattering due to electromagnetic ion cyclotron (EMIC) waves and is typically analyzed using quasi-linear theory. However, nonlinear behavior becomes significant as the wave amplitude intensifies. In this study, we aim to explore how the nonlinear behavior depends on the initial proton energy under various background plasma density conditions. The frequency of EMIC waves is 0.96Ω_He (where Ω_He is the gyrofrequency of He⁺ at the equator). It is found that the higher energy protons with nonlinear phase trapping experience more resonances, causing these trapped protons to move away from the loss cone more quickly compared to lower energy protons. However, the proportion of phase-trapped protons significantly decreases as the initial proton energy increases. This declining trend is more pronounced for a background plasma condition in the plasmapause than within the plasmasphere. The number of phase-trapped protons goes to zero as initial proton energy increases to above approximately 60 keV. Additionally, nonlinear phase bunching is more pronounced for lower energy protons (e.g., below 60 keV) compared to higher energy protons. As a result, both nonlinear phase trapping and phase bunching contribute to larger standard deviations in the net changes of equatorial pitch angle (Δ<i>α</i>_<i>eq</i>), suggesting a larger pitch agnel diffusion coefficient compared to the prediction of quasi-linear theory.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142447804","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":"Hemispheric Asymmetry of Ionospheric Poynting Flux During Geomagnetically Quiet Periods","authors":"Chao Yu,&nbsp;Xiao-Xin Zhang,&nbsp;Wenbin Wang,&nbsp;Fei He","doi":"10.1029/2024JA032519","DOIUrl":"https://doi.org/10.1029/2024JA032519","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>Using a large database containing DMSP F13 observations under geomagnetically quiet conditions from 1998 to 2009, the hemispheric asymmetries of the distribution of the Poynting flux were investigated. Significant hemispheric asymmetries were observed in both altitude-adjusted corrected geomagnetic (AACGM) and geographic coordinates, and the maximum average flux in the northern hemisphere was greater than that in the southern hemisphere by a factor of three in both coordinates. The distribution of downward Poynting flux hot-spot (DPFH) between the two hemispheres had longitudinal difference of ∼180°. The Poynting flux's hemispheric asymmetry in AACGM and geographical coordinates at different seasons were investigated. The observed seasonal variations in the Southern Hemisphere (SH) are not as significant as those in the Northern Hemisphere (NH). In addition, the downward net Poynting flux observed during the solstice period is greater than that observed for the equinox period above 60°S.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142447803","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":"Electron Dissipation and Electromagnetic Work","authors":"Yan Yang,&nbsp;杨艳,&nbsp;Subash Adhikari,&nbsp;William H. Matthaeus","doi":"10.1029/2024JA033105","DOIUrl":"https://doi.org/10.1029/2024JA033105","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>With the increase in technical capabilities of computer simulation in recent years, it has become feasible to quantify the degradation of fluid scale plasma and electromagnetic energies in favor of increases of internal energies. While it is understood that electromagnetic energy can be exchanged with fluid scale velocities, it is the pressure strain interaction that exchanges energy between fluid motions and internal energy. Here using simulations of both turbulence and reconnection we show that for electrons, the pressure strain and electromagnetic work are closely related and are frequently comparable when appropriate time and spatial averaging is applied. Otherwise, the instantaneous spatial averaged pressure strain and electromagnetic work are nearly equal for slowly evolving systems, like the reconnection case, while they differ significantly in rapidly evolving systems, like the turbulence case. This clarifies the relationship between these two quantities, which are each frequently used as measures of dissipation.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142435433","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":"Rapid Geomagnetic Variations During High-Speed Stream, Sheath and Magnetic Cloud-Driven Geomagnetic Storms From 1996 to 2023","authors":"M. N. Pedersen,&nbsp;L. Juusola,&nbsp;H. Vanhamäki,&nbsp;A. T. Aikio,&nbsp;A. Viljanen","doi":"10.1029/2024JA032656","DOIUrl":"https://doi.org/10.1029/2024JA032656","url":null,"abstract":"<p>The most detrimental geomagnetically induced currents (GICs) documented to date have all taken place during geomagnetic storms. Yet, the probability of GICs throughout geomagnetic storms driven by different solar wind transients, such as high-speed streams/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejection (ICME) sheaths and magnetic clouds (MC), is poorly understood. We present an algorithm to detect geomagnetic storms and storm phases, resulting in a catalog of 755 geomagnetic storms from January 1996 to June 2023 with the solar wind drivers. Using these storms and the IMAGE magnetometer network, we study the temporal and spatial evolution of spikes in the time derivative of the horizontal component of the external magnetic field, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>|</mo>\u0000 <mi>d</mi>\u0000 <msub>\u0000 <mi>H</mi>\u0000 <mrow>\u0000 <mi>e</mi>\u0000 <mi>x</mi>\u0000 <mi>t</mi>\u0000 </mrow>\u0000 </msub>\u0000 <mo>/</mo>\u0000 <mi>d</mi>\u0000 <mi>t</mi>\u0000 <mo>|</mo>\u0000 </mrow>\u0000 <annotation> $vert mathrm{d}{boldsymbol{H}}_{mathrm{e}mathrm{x}mathrm{t}}/mathrm{d}tvert $</annotation>\u0000 </semantics></math>, greater than 0.5 nT/s during geomagnetic storms driven by HSS/SIR, sheaths and MCs. Spikes occur more often toward the end of the storm main phase for HSS/SIR and MC-driven storms, while sheaths have spikes throughout the entire main phase. During the main phase most spikes occur in the morning sector around 05 magnetic local time (MLT) and the extent in MLT is narrowest for MCs and widest for sheaths. However, spikes in the pre-midnight sector during the main and recovery phases are most prominent for HSS/SIR-driven storms. During the storm sudden commencement (SSC), three MLT hotspots exist, the post-midnight at 04 MLT, pre-noon at 09 MLT and afternoon at 15 MLT. The pre-noon hotspot has the highest probability of spikes and the widest extent in magnetic latitude.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032656","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142435220","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":"Proton Temperature Anisotropy Constraint Associated With Alpha Beam Instability in the Solar Wind","authors":"L. Xiang,&nbsp;K. H. Lee,&nbsp;L. C. Lee,&nbsp;D. J. Wu,&nbsp;L. Chen,&nbsp;H. Q. Feng,&nbsp;Q. H. Li,&nbsp;G. Q. Zhao","doi":"10.1029/2023JA032398","DOIUrl":"https://doi.org/10.1029/2023JA032398","url":null,"abstract":"&lt;p&gt;Solar wind observations in the space of the proton temperature anisotropy &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;mrow&gt;\u0000 &lt;mi&gt;p&lt;/mi&gt;\u0000 &lt;mo&gt;⊥&lt;/mo&gt;\u0000 &lt;/mrow&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;mrow&gt;\u0000 &lt;mi&gt;p&lt;/mi&gt;\u0000 &lt;mo&gt;‖&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${T}_{pperp }/{T}_{pVert }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; versus parallel proton beta &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;β&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;p&lt;/mi&gt;\u0000 &lt;mo&gt;‖&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${beta }_{pVert }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; always show a distorted rhomboid-like pattern, where the boundaries of this plot are associated with several instabilities. However, the specific mechanism on the constraint of the proton temperature anisotropy is unclear in the low-beta &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;β&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;p&lt;/mi&gt;\u0000 &lt;mo&gt;‖&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;&lt;&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${beta }_{pVert }&lt; 1$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; plasma. In this work, we study the kinetic instabilities driven by proton temperature anisotropy and alpha beam with the Vlasov theory and investigate the nonlinear evolution of these instabilities with hybrid simulations. We also compare the theoretical and simulation results with Wind observations. The alpha beam with drift velocity &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;v&lt;/mi&gt;\u0000 &lt;mi&gt;α&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;/&lt;/mo&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;v&lt;/mi&gt;\u0000 &lt;mi&gt;A&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;&gt;&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${v}_{alpha }/{v}_{A} &gt; 1$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; leads to a new kind of Alfvén/ion-cyclotron instability (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;α&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $alpha $&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;A/IC instability) in the region of &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 ","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142429900","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":"Electron Pitch Angle Distributions in Magnetotail Tailward Flows","authors":"Y. Y. Wei,&nbsp;S. Y. Huang,&nbsp;K. Jiang,&nbsp;Z. G. Yuan,&nbsp;S. B. Xu,&nbsp;J. Zhang,&nbsp;Q. Y. Xiong,&nbsp;Z. Wang,&nbsp;R. T. Lin,&nbsp;L. Yu","doi":"10.1029/2024JA032596","DOIUrl":"https://doi.org/10.1029/2024JA032596","url":null,"abstract":"<p>Electron pitch angle distributions (PADs) are crucial to revealing electron acceleration and heating in geospace. The electron PADs in the Earth's magnetotail have been widely studied by statistical or case analysis. However, the statistical features of electron PADs in tailward flows are still unclear. We survey data from the Magnetospheric Multiscale (MMS) satellite to statistically investigate electron PADs in tailward flows in the Earth's magnetotail for the first time. We find that for most (66.3%) tailward flows, electrons with energy from 0.1 to 30 keV are mainly field-aligned. The PADs of suprathermal (&gt;2 keV) electrons in a part of tailward flows (26.3%) are mostly isotropic. Additionally, the perpendicular-dominated PADs of suprathermal electrons only exist in a few (7.4%) tailward flows. According to the different dominant PADs of suprathermal electrons, the tailward flows are classified into three types: field-aligned-dominated type, isotropic-dominated type and perpendicular-dominated type flows. The dependence of electron PADs on plasma environmental parameters is investigated in these three types of flows. For field-aligned-dominated type flows, the field-aligned anisotropy decreases toward the central plasma sheet (CPS) and with the increase of the energy. In addition, it is found that the field-aligned anisotropy in the field-aligned-dominated tailward flows reduces noticeably when the |<i>V</i>_ix| exceeds 800 km/s. In isotropic-dominated type flows, the field-aligned anisotropy of electrons with energy ≥10 keV also shows a slight decreasing trend toward the CPS. For perpendicular-dominated type flows, the perpendicular anisotropy exhibits two non-monotonic processes, initially increasing and then decreasing with the increase of distance from the CPS; while becomes more evident for higher energy electrons. Our statistical results indicate that in tailward flows, electron anisotropy depends on the distance from the CPS, energy and plasma flow velocity. Tailward flows are associated with the transport of plasma toward the distant tail, and the statistical analysis of electron PADs in these flows can improve our understanding of the related electron dynamics in the magnetotail.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142429726","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":"A Three-Frequency Ca+ Doppler Lidar for Ion Temperature Measurements in the E and F Regions","authors":"Fang Wu,&nbsp;Jing Jiao,&nbsp;Lifang Du,&nbsp;Haoran Zheng,&nbsp;Zelong Wang,&nbsp;Xuewu Cheng,&nbsp;Fuju Wu,&nbsp;Yuan Xia,&nbsp;Jiqin Wang,&nbsp;Wei Wang,&nbsp;Kexin Wang,&nbsp;Yuchang Xun,&nbsp;Jiyao Xu,&nbsp;Yajun Zhu,&nbsp;Wei Yuan,&nbsp;Weijun Liu,&nbsp;Guotao Yang","doi":"10.1029/2024JA032511","DOIUrl":"https://doi.org/10.1029/2024JA032511","url":null,"abstract":"<p>The ion temperature is an important parameter for ionospheric detection, yet there is limited research on ion temperatures at altitude range from 80 to 300 km. Currently, a single-frequency Ca⁺ ion optical parametric oscillator (OPO) Lidar system can be used to obtain the Ca⁺ ion density in this region at Yanqing Station, Beijing (40.4°N, 116.0°E). In this study, the ion temperature can be obtained by extending our original lidar to include three-frequency Ca⁺ Doppler detection. This development represents a pioneering step on measuring ion temperatures by lidar in the ionospheric E-F region. Preliminary results in the E region show that lidar temperatures at 90–105 km under the condition of smooth changes in Ca⁺ ion morphology align reasonably with satellite-based observations and model-derived temperatures. Additionally, the exploratory ion temperatures of the F layer peak heights at 200–300 km were obtained. Furthermore, parameter optimization and temperature error analysis in the E-F region are explored, providing valuable insights for the development of Ca⁺ Doppler lidar systems. The advent of Ca⁺ Doppler lidar has greatly expanded the lidar detection altitude range of temperature and the possibilities for in-depth research on ion temperature and velocity in regions affected by complex electrodynamic effects. These findings lay the foundation for subsequent studies of coupling processes in the ionospheric E-F region.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142429912","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 in Jupiter's Nightside Magnetosphere and Related Radial Currents","authors":"G. Provan,&nbsp;S. W. H. Cowley,&nbsp;J. D. Nichols","doi":"10.1029/2024JA032677","DOIUrl":"https://doi.org/10.1029/2024JA032677","url":null,"abstract":"<p>We combine magnetic data from the first 46 data-taking periapsides of the polar orbiting Juno spacecraft spanning dawn to dusk via midnight to investigate azimuthal fields and related currents in Jupiter's nightside magnetosphere. Data are binned by perpendicular radial distance <i>ρ</i> from the magnetic axis over 4–32 R_J along empirical poloidal model field lines spanning from tail to middle magnetosphere regions (ionospheric colatitudes <i>θ</i>_<i>i</i> ∼ 5°–17°), and by local time (LT). The data are well organized by these parameters. On southern tail field lines (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mrow>\u0000 <mo>∼</mo>\u0000 <mrow>\u0000 <mn>5</mn>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <mo>&lt;</mo>\u0000 <mi>θ</mi>\u0000 </mrow>\u0000 <mi>i</mi>\u0000 </msub>\u0000 <mo>≤</mo>\u0000 <mrow>\u0000 <mn>11</mn>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> ${sim 5{}^{circ}&lt; theta }_{i}le 11{}^{circ}$</annotation>\u0000 </semantics></math>) the azimuthal field is well represented as the sum of sweepback fields falling as 1/<i>ρ</i> that are near-independent of <i>θ</i>_<i>i</i> and LT, and a near-constant field consistent with ∼3.5 nT pointing sunward. The combination is swept back at dawn/midnight but swept forward at dusk outside ∼5 R_J. Outer magnetosphere (<i>θ</i>_<i>i</i> ∼ 12°–15.5°) azimuthal fields are instead swept back near-independent of LT, near-continuous with the tail field in the dawn sector, but with large shear at the tail interface and across outer magnetosphere field lines in the dusk-midnight sector. The tail region 1/<i>ρ</i> field is associated with a nightside inward polar axial current ∼5.8 MA located within <i>θ</i>_<i>i</i> ∼ 5° of the magnetic axis, while the dusk-midnight field shear measured near the ∼30 R_J study boundary provides an inward current ∼15.4 MA, related to the near-constant field. Azimuthal fields fall to small values across middle magnetosphere field lines (<i>θ</i>_<i>i</i> ∼ 15.5°–17°), associated with outward currents ∼21.2 MA per hemisphere near-independent of LT forming the nightside equatorial current sheet, balancing these inward currents.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032677","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142429926","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":"Secondary Gravity Wave Propagation in Tropical Thermospheric Region: Role of Varying Kinematic Viscosity","authors":"Soumen Datta,&nbsp;Saurabh Das,&nbsp;Surendra Sunda","doi":"10.1029/2023JA032364","DOIUrl":"https://doi.org/10.1029/2023JA032364","url":null,"abstract":"<p>The current study has investigated the thunderstorm induced atmospheric gravity waves (AGWs) over Indian region based on the perturbation signatures in ionospheric total electron content (TEC) measurement. Robust traveling ionospheric disturbance (TID) signature has been identified along the east side of the thunderstorm affected area. Neutral wind was found to have a favorable impact in this aspect for a certain time duration of the day by modulating the vertical wavelength. The role of temperature was analyzed in terms of kinematic viscosity which is a crucial component, especially over tropical region, for wave dissipation and reflection along its propagation path. Ray tracing algorithm is also applied with varying kinematic viscosity and thermal diffusivity for retrieval of possible ray paths and source location of observed waves. A statistical investigation has been carried out to identify the dissipation altitude of observed waves along the ray paths. It has been found that all waves dissipated at almost a constant altitude for a specific kinematic viscosity and above this altitude vertical wavelength was found to decrease. The ray paths interacted at a common point which was located at about 125 km altitude and was very close to the region of maximum lightning activity. It can also be noted that the observed phase velocities can't be achieved by a wave below the turbopause. It indicates that the observed waves were excited from a secondary source and not directly connected to convective system. The study provides an in-depth analysis of mesoscale system induced gravity wave propagation and dissipation over tropical region.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142429651","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}