Journal of Geophysical Research: Space Physics最新文献

{"title":"Categorization of Electron Isotropy Boundary Patterns: ELFIN and POES Observations","authors":"A. V. Artemyev,&nbsp;V. A. Sergeev,&nbsp;V. Angelopoulos,&nbsp;X.-J. Zhang,&nbsp;C. Wilkins","doi":"10.1029/2024JA033231","DOIUrl":"https://doi.org/10.1029/2024JA033231","url":null,"abstract":"<p>Magnetic field-line curvature scattering (FLCS) of energetic particles in the equatorial magnetotail results in isotropization of pitch-angle distributions, loss-cone filling, and precipitation above a minimum energy at a given latitude. At a fixed energy, the lowest latitude of isotropization is the isotropy boundary (IB) for that energy. Nominally, the IB (latitude) exhibits a characteristic energy dependence due to the monotonic variation of the equatorial magnetic field intensity <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>B</mi>\u0000 <mrow>\u0000 <mi>e</mi>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${B}_{eq}$</annotation>\u0000 </semantics></math> with radial distance. Deviations from this nominal IB dispersion can occur if the radial <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>B</mi>\u0000 <mrow>\u0000 <mi>e</mi>\u0000 <mi>q</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${B}_{eq}$</annotation>\u0000 </semantics></math> variation (spatial or temporal) is non-mononotic and/or if other precipitation mechanisms prevail. With its sensitive and detailed measurements of electron spectra up to relativistic energies, ELFIN's recent observations reveal a variety of electron IBe patterns near magnetic midnight which are repeatable enough to warrant classification. This study aims to categorize the various IBe patterns observed by ELFIN's high-fidelity but short lived dataset (a few months), compare them with simultaneous nearby POES observations, which are made with a limited energy coverage and resolution but last for decades, and discuss their possible interpretation. The general agreement between ELFIN and POES IB observations indicate a relatively large-scale nature of IBe patterns. Surprisingly, there exists a large number (up to 2/3 of all events) of non-monotonic-or steep/multiple-IB patterns. This suggest an abundance of non-trivial tail current sheet structures or a mixed contribution of two mechanisms in the vicinity of IBe in these cases.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758112","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":"Simultaneous Infrared Observations of the Jovian Auroral Ionosphere and Thermosphere","authors":"Ruoyan Wang,&nbsp;Tom S. Stallard,&nbsp;Henrik Melin,&nbsp;Kevin H. Baines,&nbsp;Luke Moore,&nbsp;James O’Donoghue,&nbsp;Rosie E. Johnson,&nbsp;Emma M. Thomas,&nbsp;Katie L. Knowles,&nbsp;Paola I. Tiranti,&nbsp;Steve Miller","doi":"10.1029/2024JA032891","DOIUrl":"https://doi.org/10.1029/2024JA032891","url":null,"abstract":"&lt;p&gt;Simultaneous observations of &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;3&lt;/mn&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{3}^{+}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; and &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;H&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; in Jupiter's northern infrared aurora were conducted on 02 June 2017 using Keck-NIRSPEC to produce polar projection maps of &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;3&lt;/mn&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{3}^{+}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; radiance, rotational temperature, column density, and &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;H&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; radiance. The temperature variations within the auroral region are &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;700&lt;/mn&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1000&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${sim} 700-1000$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; K, generally consistent with previous studies, albeit with some structural differences. Known auroral heating sources including particle precipitation, Joule heating, and ion drag have been examined by studying the correlations between each derived quantity, yet no single dominant mechanism can be identified as the main driver for the energetics in Jupiter's northern auroral region. It appears that a complex interaction exists between the heating driven by various mechanisms and the cooling from the &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mn&gt;3&lt;/mn&gt;\u0000 &lt;mo&gt;+&lt;/mo&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{H}}_{3}^{+}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; thermostat effect. Comparisons between the &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubs","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032891","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142758051","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":"Convective Growth of Auroral Arcs Through the Feedback Instability in a Dipole Geometry","authors":"T. Sakaki,&nbsp;T.-H. Watanabe,&nbsp;S. Maeyama","doi":"10.1029/2023JA032407","DOIUrl":"https://doi.org/10.1029/2023JA032407","url":null,"abstract":"<p>Auroral dynamics in the magnetosphere-ionosphere (M-I) coupling system with the dipole magnetic field is investigated by means of a novel simulation code developed with flux coordinates where a set of the reduced magnetohydrodynamic (MHD) and the two-fluid equations for the M-I coupling system is numerically solved. The linear simulations of the feedback instability reveal that a wave packet of auroral arcs propagating in the north-south direction is amplified through the feedback instability, and that the convective growth of auroral structures with enhancement of the ionospheric density and the field aligned current ceases because of the latitudinal dependence of the field line length. These properties are elucidated in terms of the local dispersion relation of the feedback instability for fixed real frequencies.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749300","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":"Density Troughs in the Ionosphere Sustained by Transport Barriers","authors":"M. A. Malkov,&nbsp;V. I. Sotnikov,&nbsp;E. V. Mishin","doi":"10.1029/2024JA032838","DOIUrl":"https://doi.org/10.1029/2024JA032838","url":null,"abstract":"<p>This study explores the relaxation and sustainability of density irregularities and plasma flows in the Earth's ionosphere. To do this, we use a modified model of drift-wave turbulence known as the Hasegawa-Wakatani model. Similar to turbulent processes in laboratory plasmas, we explore a powerful mechanism that can reduce the turbulent plasma transport. This mechanism is associated with the creation of “zonal flows,” cutting across the gradients of particle density and magnetic fields. They work effectively to minimize particles' random movement and reduce the turbulence causing this movement. The zonal flows create transport barriers in areas where the density gradient is steepest and where drift waves grow most vigorously. The transport barriers significantly delay the refill of low-density regions with surrounding plasma. They also lead to changes in the electric potential of the plasma and influence the movement of ions in the direction of the magnetic field. Our research investigates how these zonal flows are generated and how effectively they sustain density irregularities. We also examine the spectral characteristics of turbulence in and around these barriers.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749305","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 Parametric Study of Quasi-Static Electron Acceleration by Modified Electron Acoustic Wave and Comparison to Knight Relation","authors":"Run Shi,&nbsp;Jun Liang,&nbsp;Zejun Hu,&nbsp;Desheng Han,&nbsp;Yating Xiong","doi":"10.1029/2024JA033183","DOIUrl":"https://doi.org/10.1029/2024JA033183","url":null,"abstract":"<p>A comprehensive understanding of how a magnetic source potential is distributed in the magnetosphere-ionosphere circuit, and the relationship between the field-aligned current and the parallel potential, is essential for accurately interpreting the observational characteristics of a quasi-static arc. In this study, we investigate the formation of quasi-static electron acceleration led by kinetic Alfvén wave-electron acoustic wave coupling, based on one-dimensional kinetic simulations. Various controlling factors of the coupling process are considered, including the hot electron density and temperature, the cold electron density and temperature, the perpendicular wave number, and the ionospheric conductance. The ratio between the parallel potential drop and field-aligned current is found to be approximately proportional to the square root of the hot electron temperature and inversely proportional to the hot electron density, similar to the Knight relation but with a modified slope factor that depends on the perpendicular wavelength and cold electron parameters. Meanwhile, with smaller perpendicular wavelength, lower hot electron density, higher hot electron temperature, and lower cold electron density, more potential drop is applied to the parallel electron acceleration in the transition region.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749299","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":"Statistics of Higher Harmonics SRS at Low Latitude Station, Shillong","authors":"P. Adhitya,&nbsp;Jayashree Bulusu,&nbsp;Masahito Nosé,&nbsp;Geeta Vichare,&nbsp;A. P. Dimri","doi":"10.1029/2024JA033034","DOIUrl":"https://doi.org/10.1029/2024JA033034","url":null,"abstract":"&lt;p&gt;This is the first statistical ground investigation of unique low latitude Spectral Resonance Structures (SRS) that increase beyond &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;5&lt;/mn&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mi&gt;z&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $5,Hz$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;, crossing the fundamental Schumann resonance at few occurrences. The study is carried out using high resolution magnetic field variation data obtained from induction coil magnetometer (ICM) installed at very low latitude Indian station, Shillong (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;25.56&lt;/mn&gt;\u0000 &lt;mo&gt;°&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $25.56mathit{{}^{circ}},N$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; geographic latitude, &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;91.86&lt;/mn&gt;\u0000 &lt;mo&gt;°&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;E&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $91.86mathit{{}^{circ}},E$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; geographic longitude, &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;d&lt;/mi&gt;\u0000 &lt;mi&gt;i&lt;/mi&gt;\u0000 &lt;mi&gt;p&lt;/mi&gt;\u0000 &lt;mi&gt;o&lt;/mi&gt;\u0000 &lt;mi&gt;l&lt;/mi&gt;\u0000 &lt;mi&gt;e&lt;/mi&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;L&lt;/mi&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;1.08&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $dipole,L=1.08$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;) for the duration 2013–2018. This study focuses on the characteristics of SRS whose harmonic frequencies reach &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;5&lt;/mn&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mi&gt;z&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $5,Hz$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; and above. The study reveals that the occurrence of SRS events above &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;5&lt;/mn&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mi&gt;H&lt;/mi&gt;\u0000 &lt;mi&gt;z&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $5,Hz$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; is higher in winter as compared to summer, also the occurrence is higher during low solar activity period as compared to period of solar maximum. It is seen that both the cavities, viz. Ionospheric Alfven Resonator (IAR) and Magnetospheric Alfven Resonator (MAR) support such SRS and have their r","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749108","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 Parameters Dataset From Juno/JADE Observations in Jupiter's Magnetosphere Between 10 and 50 RJ","authors":"Jian-zhao Wang,&nbsp;Fran Bagenal,&nbsp;Robert J. Wilson,&nbsp;Philip W. Valek,&nbsp;Robert W. Ebert,&nbsp;Frederic Allegrini","doi":"10.1029/2024JA033454","DOIUrl":"https://doi.org/10.1029/2024JA033454","url":null,"abstract":"<p>After its arrival at Jupiter in July 2016, Juno conducted a global survey of Jupiter's magnetosphere (especially the equatorial plasma disk region) with its highly eccentric polar orbit. Since then, the JADE instrument has accumulated a large amount of plasma measurements. Using a developed forward modeling method and the Alpine supercomputer cluster at CU Boulder, we fit all ion measurements between 10 and 50 <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>R</mi>\u0000 <mi>J</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${mathrm{R}}_{mathrm{J}}$</annotation>\u0000 </semantics></math> from PJ5 to PJ56, obtaining a dataset with 70,487 good fits that consists of the following set of plasma parameters: abundances of different heavy ions, density, temperature, and 3-D bulk flow velocity of heavy ions. An overview of the dataset and an example use on flux tube interchange are presented to illustrate its effectiveness and usefulness. In the investigated interchange event that occurred at <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>∼</mo>\u0000 </mrow>\u0000 <annotation> ${sim} $</annotation>\u0000 </semantics></math>14 <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>R</mi>\u0000 <mi>J</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${mathrm{R}}_{mathrm{J}}$</annotation>\u0000 </semantics></math>, the plasma disk is variable and heated, with alternating hotter inflows and colder outflows, accompanied by small perturbations in the magnetic fields. This dataset has the potential for many applications.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749302","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 Novel Determination of the Foreshock ULF Boundary: Statistical Approach","authors":"A. Salohub,&nbsp;J. Šafránková,&nbsp;Z. Němeček,&nbsp;G. Pi","doi":"10.1029/2024JA033195","DOIUrl":"https://doi.org/10.1029/2024JA033195","url":null,"abstract":"<p>The location and spatial extent of the region populated by the foreshock waves depend on the IMF orientation. We performed a systematic statistical study of wave activity in the frequency range of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>0.03</mn>\u0000 <mo>−</mo>\u0000 <mn>0.15</mn>\u0000 </mrow>\u0000 <annotation> $0.03-0.15$</annotation>\u0000 </semantics></math> Hz observed during an initial phase of the THEMIS mission. Wave activity is quantified by standard deviations of the IMF magnitude and its components over 10-min intervals. We apply the foreshock coordinate system defined as the angle between the bow shock normal and upstream magnetic field vectors and the distance from the spacecraft to bow shock along the magnetic field line. We have found that the Ultra-low Frequency (ULF) foreshock boundary (a) is well defined in these coordinates, (b) it tends to shift outward with an increasing solar wind bulk speed, and (c) with an increasing Mach number. However, the change of the fluctuation level in the foreshock is not uniform because the increasing solar wind bulk speed enhances the fluctuation level mainly in a close proximity of the bow shock whereas the increasing Mach number leads to an intensification of fluctuation levels at the foreshock boundary.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA033195","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749103","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":"Refraction of ELF Electromagnetic Waves by the Ionospheric Gradients at the Day/Night Terminator Measured at the Hylaty Station","authors":"M. Ostrowski,&nbsp;M. Gołkowski,&nbsp;J. Kubisz,&nbsp;A. Michalec,&nbsp;J. Mlynarczyk,&nbsp;Z. Nieckarz","doi":"10.1029/2024JA033274","DOIUrl":"https://doi.org/10.1029/2024JA033274","url":null,"abstract":"<p>We perform azimuth time tracking of multiple thunderstorm centers on the globe, which are sources of extremely low frequency (ELF) electromagnetic waves propagating in the spherical Earth-ionosphere cavity. For observations made in September 2023 we identify azimuths of numerous global emission centers using our data sampled at 3 kHz at the Hylaty station in Poland. We confirm significant and relatively regular thunderstorm azimuth variation during the solar terminator passage over the observation site. The magnitude and duration of the azimuth deviations depend on the observed azimuths but are also varying between successive days and changing detailed thunderstorm activity patterns. The measured maximum positive (preferentially at the sunrise time) and negative (preferentially at the sunset time) azimuth deviations reach even above 20<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <annotation> $mathit{{}^{circ}}$</annotation>\u0000 </semantics></math> for waves propagating close to the terminator. We discovered also particular composite deviation structures, with the negative azimuth deviation directly preceding a larger positive one, sometimes occurring near the morning terminator passage 100 km above the surface. It is possibly the first detection of the ELF equivalent of the “greyline” transmission known in the HF radio propagation. At azimuths distant from the terminator one can observe decreasing of the regular deviation magnitude and occasionally lower magnitude deviations with opposite sign. The variations between successive days are expected to result from varying thunderstorm activity on Earth as well variability of ionospheric parameters, in particular of ionization gradients and nonuniformities occurring along the terminator. We postulate that the observed deviations result from a signal refraction at the varying ionospheric gradients.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749306","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":"Impact of Interplanetary Magnetic Field By on Subauroral Polarization Streams at Dawn and Dusk","authors":"Yu Sun,&nbsp;Hui Wang,&nbsp;Kedeng Zhang","doi":"10.1029/2024JA033063","DOIUrl":"https://doi.org/10.1029/2024JA033063","url":null,"abstract":"<p>This study uses 8 years of DMSP data to examine how the polarity of the interplanetary magnetic field (IMF) <i>B</i>_<i>y</i> influences the strength and latitude of subauroral polarization streams (SAPS), alongside field-aligned currents (FACs). Significant local time, seasonal, and hemispheric differences are observed. At dusk, R1 (Region 1) FACs are found poleward and R2 (Region 2) FACs equatorward of peak SAPS; at dawn, SAPS are positioned equatorward of upward R2 FACs. In the Northern Hemisphere (NH), SAPS are stronger under IMF <i>B</i>_<i>y</i> &gt; 0 at dusk, while in the Southern Hemisphere (SH), SAPS are stronger under IMF <i>B</i>_<i>y</i> &lt; 0. Dawnside SAPS tends to be stronger under IMF <i>B</i>_<i>y</i> &lt; 0. Duskside R1 FACs are stronger under IMF <i>B</i>_<i>y</i> &lt; 0, with seasonal variations in R2 FACs, whereas dawnside R2 FACs prefer IMF <i>B</i>_<i>y</i> &gt; 0. SAPS latitudes vary seasonally with IMF <i>B</i>_<i>y</i> polarity, showing more poleward SH SAPS under IMF <i>B</i>_<i>y</i> &gt; 0. Ionospheric upflows exhibit similar IMF <i>B</i>_<i>y</i> polarity dependence as SAPS at dusk, but this influence diminishes at dawn. Model simulations underscore how IMF <i>B</i>_<i>y</i> affects SAPS dynamics through FACs and conductivity gradients, highlighting larger NH (SH) SAPS under positive IMF <i>B</i>_<i>y</i> at dusk (dawn) compared to its SH (NH) counterpart.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":"129 12","pages":""},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142749304","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}