Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data, we studied the stepwise development in high-latitude geomagnetic perturbations and Pi1 and Pi2 pulsations during substorm onsets and their association with stepwise auroral onset arc development by analyzing four substorm events. We found that the geomagnetic perturbations and pulsations which are magnetic signatures of the substorm on the ground show stepwise changes and excitation similar to the development of the auroral onset arc which is the visual manifestation of the substorm. We observed minor to small changes in magnetic perturbations and excitation of Pi2 pulsations before initial brightening (IB), and the subsequent excitation of Pi1 and the second Pi2 at or around the further enhancement of onset arc (FE). Then, a steep fall in the magnetic northward component, and the largest-amplitude and highest-frequency Pi1 and Pi2 pulsations appeared at or after poleward expansion (PE). The appearance of FE in all four events and its association with magnetic perturbations and pulsations suggest that FE is an important step in addition to IB and PE. The detailed analysis of the FE step using ground- and space-based data may provide information on the substorm triggering mechanism, the sequence of mechanisms behind the substorm, as well as the mechanisms responsible for the excitation of Pi1 and Pi2 pulsations.
{"title":"Association of High-Latitude Geomagnetic Perturbations and Pi1 and Pi2 Pulsations With the Three Steps of Auroral Onset Arc Development at Substorm Onset","authors":"Madeeha Talha, Yukinaga Miyashita","doi":"10.1029/2024JA032595","DOIUrl":"https://doi.org/10.1029/2024JA032595","url":null,"abstract":"<p>Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data, we studied the stepwise development in high-latitude geomagnetic perturbations and Pi1 and Pi2 pulsations during substorm onsets and their association with stepwise auroral onset arc development by analyzing four substorm events. We found that the geomagnetic perturbations and pulsations which are magnetic signatures of the substorm on the ground show stepwise changes and excitation similar to the development of the auroral onset arc which is the visual manifestation of the substorm. We observed minor to small changes in magnetic perturbations and excitation of Pi2 pulsations before initial brightening (IB), and the subsequent excitation of Pi1 and the second Pi2 at or around the further enhancement of onset arc (FE). Then, a steep fall in the magnetic northward component, and the largest-amplitude and highest-frequency Pi1 and Pi2 pulsations appeared at or after poleward expansion (PE). The appearance of FE in all four events and its association with magnetic perturbations and pulsations suggest that FE is an important step in addition to IB and PE. The detailed analysis of the FE step using ground- and space-based data may provide information on the substorm triggering mechanism, the sequence of mechanisms behind the substorm, as well as the mechanisms responsible for the excitation of Pi1 and Pi2 pulsations.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141608071","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}
Observational data sets for the high latitude middle atmosphere are key to understand the dynamics over those latitudes and the coupling between the lower and middle atmosphere. Utilizing long-term data sets from an all-sky imager at Tromsø, Norway (69.6°N, 19.2°E), the characteristics of 18 mesospheric frontal events in the Arctic winter mesosphere from 2011 to 2015 were studied. These frontal events exhibit horizontal extensions exceeding 500 km and were characterized by a sharp leading front, sometimes followed by a quasi-monochromatic wave train or a turbulent region. A subset of these frontal gravity wave events has been identified in the past as “bores.” While there have been numerous previous reports from low- and mid-latitude sites, and also from southern high latitudes, there have been a few from northern high latitudes. This study focuses on the frontal events in the northern high latitudes and provides new insights into the characteristics of these events. Their horizontal wavelengths primarily ranged from 20 to 40 km, and they exhibited phase speeds in the range 30–80 m/s. Most events were observed before local midnight. No clear link between these events and auroral activity was found. The majority of fronts were found propagating in the north-west direction, which might be due to the wind filtering effects.
{"title":"Occurrence of Mesospheric Frontal Structures Over the High Latitude Station, Tromsø, Norway","authors":"Nilesh Chauhan, Kazuo Shiokawa, S. Gurubaran, Satonori Nozawa, Shin-ichiro Oyama, Takuji Nakamura","doi":"10.1029/2023JA032243","DOIUrl":"https://doi.org/10.1029/2023JA032243","url":null,"abstract":"<p>Observational data sets for the high latitude middle atmosphere are key to understand the dynamics over those latitudes and the coupling between the lower and middle atmosphere. Utilizing long-term data sets from an all-sky imager at Tromsø, Norway (69.6°N, 19.2°E), the characteristics of 18 mesospheric frontal events in the Arctic winter mesosphere from 2011 to 2015 were studied. These frontal events exhibit horizontal extensions exceeding 500 km and were characterized by a sharp leading front, sometimes followed by a quasi-monochromatic wave train or a turbulent region. A subset of these frontal gravity wave events has been identified in the past as “bores.” While there have been numerous previous reports from low- and mid-latitude sites, and also from southern high latitudes, there have been a few from northern high latitudes. This study focuses on the frontal events in the northern high latitudes and provides new insights into the characteristics of these events. Their horizontal wavelengths primarily ranged from 20 to 40 km, and they exhibited phase speeds in the range 30–80 m/s. Most events were observed before local midnight. No clear link between these events and auroral activity was found. The majority of fronts were found propagating in the north-west direction, which might be due to the wind filtering effects.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141596986","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}
Utilizing the multi-point observations by Van Allen Probe A, GOES 13 and 15, we analyzed the competing influences of earthward convection and azimuthal drift loss on the pitch angle distributions of energetic electrons during the simultaneous increases in solar wind flow velocity and pressure. The increase in solar wind speed amplifies the dawn-dusk convection electric field and causes the earthward transport of energetic electrons, and meanwhile the enhancement of solar wind dynamic pressure causes the inward displacement of dayside magnetopause and triggers the azimuthal drift loss of energetic electrons. The earthward convection of low-energy electrons (<60 keV) is much faster than their azimuthal drift loss at most pitch angles, and the fast earthward convections make the butterfly-like electron pitch angle distributions formed early become pancake-like distributions. The 60–530 keV electrons maintain the butterfly-like pitch angle distributions during the earthward convections, whereas the high-energy electrons above 530 keV are not transported to the low-L shells because of fast drift loss in the high-L source region. The competition between the earthward convection and the azimuthal drift loss finally determines the pitch angle distributions of energetic electrons near the trapping boundary during the increases in solar wind flow speed and pressure.
{"title":"Competing Influences of Earthward Convection and Azimuthal Drift Loss on the Pitch Angle Distribution of Energetic Electrons","authors":"H. C. Yuan, L. Y. Li, L. Yang, J. B. Cao","doi":"10.1029/2024JA032534","DOIUrl":"https://doi.org/10.1029/2024JA032534","url":null,"abstract":"<p>Utilizing the multi-point observations by Van Allen Probe A, GOES 13 and 15, we analyzed the competing influences of earthward convection and azimuthal drift loss on the pitch angle distributions of energetic electrons during the simultaneous increases in solar wind flow velocity and pressure. The increase in solar wind speed amplifies the dawn-dusk convection electric field and causes the earthward transport of energetic electrons, and meanwhile the enhancement of solar wind dynamic pressure causes the inward displacement of dayside magnetopause and triggers the azimuthal drift loss of energetic electrons. The earthward convection of low-energy electrons (<60 keV) is much faster than their azimuthal drift loss at most pitch angles, and the fast earthward convections make the butterfly-like electron pitch angle distributions formed early become pancake-like distributions. The 60–530 keV electrons maintain the butterfly-like pitch angle distributions during the earthward convections, whereas the high-energy electrons above 530 keV are not transported to the low-L shells because of fast drift loss in the high-L source region. The competition between the earthward convection and the azimuthal drift loss finally determines the pitch angle distributions of energetic electrons near the trapping boundary during the increases in solar wind flow speed and pressure.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141596987","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}
Bharati Kakad, Amar Kakad, Yoshiharu Omura, Peter H. Yoon
The present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left-hand (LH), and higher frequency harmonics are associated with the right-hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi-perpendicular directions to the ambient magnetic field. The results of linear theory and Particle-In-Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.
{"title":"First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region","authors":"Bharati Kakad, Amar Kakad, Yoshiharu Omura, Peter H. Yoon","doi":"10.1029/2024JA032538","DOIUrl":"https://doi.org/10.1029/2024JA032538","url":null,"abstract":"<p>The present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (<i>f</i><sub><i>ci</i></sub> ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of <i>f</i><sub><i>ci</i></sub>. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left-hand (LH), and higher frequency harmonics are associated with the right-hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi-perpendicular directions to the ambient magnetic field. The results of linear theory and Particle-In-Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141584064","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}
M. A. Clilverd, C. J. Rodger, A. T. Hendry, A. R. Lozinski, J.-A. Sauvaud, M. R. Lessard, T. Raita
High energy resolution DEMETER satellite observations from the Instrument for the Detection of Particle (IDP) are analyzed during an electromagnetic ion cyclotron (EMIC)-induced electron precipitation event. Analysis of an Interval Pulsation with Diminishing Periods (IPDP)-type EMIC wave event, using combined satellite observations to correct for incident proton contamination, detected an energy precipitation spectrum ranging from ∼150 keV to ∼1.5 MeV. While inconsistent with many theoretical predictions of >1 MeV EMIC-induced electron precipitation, the finding is consistent with an increasing number of experimentally observed events detected using lower resolution integral channel measurements on the POES, FIREBIRD, and ELFIN satellites. Revised and improved DEMETER differential energy fluxes, after correction for incident proton contamination shows that they agree to within 40% in peak flux magnitude, and 85 keV (within 40%) for the energy at which the peak occurred as calculated from POES integral channel electron precipitation measurements. This work shows that a subset of EMIC waves found close to the plasmapause, that is, IPDP-type rising tone events, can produce electron precipitation with peak energies substantially below 1 MeV. The rising tone features of IPDP EMIC waves, along with the association with the high cold plasma density regime, and the rapidly varying electron density gradients of the plasmapause may be an important factor in the generation of such low energy precipitation, co-incident with a high energy tail. Our work highlights the importance of undertaking proton contamination correction when using the high-resolution DEMETER particle measurements to investigate EMIC-driven electron precipitation.
{"title":"Improved Energy Resolution Measurements of Electron Precipitation Observed During an IPDP-Type EMIC Event","authors":"M. A. Clilverd, C. J. Rodger, A. T. Hendry, A. R. Lozinski, J.-A. Sauvaud, M. R. Lessard, T. Raita","doi":"10.1029/2024JA032785","DOIUrl":"https://doi.org/10.1029/2024JA032785","url":null,"abstract":"<p>High energy resolution DEMETER satellite observations from the Instrument for the Detection of Particle (IDP) are analyzed during an electromagnetic ion cyclotron (EMIC)-induced electron precipitation event. Analysis of an Interval Pulsation with Diminishing Periods (IPDP)-type EMIC wave event, using combined satellite observations to correct for incident proton contamination, detected an energy precipitation spectrum ranging from ∼150 keV to ∼1.5 MeV. While inconsistent with many theoretical predictions of >1 MeV EMIC-induced electron precipitation, the finding is consistent with an increasing number of experimentally observed events detected using lower resolution integral channel measurements on the POES, FIREBIRD, and ELFIN satellites. Revised and improved DEMETER differential energy fluxes, after correction for incident proton contamination shows that they agree to within 40% in peak flux magnitude, and 85 keV (within 40%) for the energy at which the peak occurred as calculated from POES integral channel electron precipitation measurements. This work shows that a subset of EMIC waves found close to the plasmapause, that is, IPDP-type rising tone events, can produce electron precipitation with peak energies substantially below 1 MeV. The rising tone features of IPDP EMIC waves, along with the association with the high cold plasma density regime, and the rapidly varying electron density gradients of the plasmapause may be an important factor in the generation of such low energy precipitation, co-incident with a high energy tail. Our work highlights the importance of undertaking proton contamination correction when using the high-resolution DEMETER particle measurements to investigate EMIC-driven electron precipitation.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032785","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141583922","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}
Gang Chen, Xuesi Cai, Shaodong Zhang, Wanlin Gong, Guotao Yang, Yungang Wang, Lianhuan Hu, Dingkun Zhong, Yaxian Li, Yimeng Xu, Min Zhang, Pengfei Hu
Solar eclipse traveled across South China in the afternoon on 21 June 2020. Five ionosondes located from mid-to low-latitudes and on both north and south of the eclipse path were applied to investigate the ionospheric responses. Both the zonal and meridional ranges of the observation region have exceeded 1,000 km. All the five ionosondes had observed the Intermediate Descending Layers (IDLs) simultaneously just after the eclipse maximum and this is a very small probability event. During the solar eclipse, the multi-hop echoes above the Es, the rising Es to 150 km altitude, the plasma flux from above F2-layer were also observed and analyzed. The descending trend of the IDLs and the peak height of F2-layer (hmF2) shows great consistency, indicating the close relationship between the eclipse induced plasma flux and the IDLs. The traces of gravity waves were also found in the IDLs and F-layer. The plasma flux may carry the ions to valley region and the eclipse produced gravity waves were responsible for the formation of the IDLs.
{"title":"Intermediate Descending Layers Emerged Simultaneously in Five Different Locations During the Solar Eclipse on 21 June 2020","authors":"Gang Chen, Xuesi Cai, Shaodong Zhang, Wanlin Gong, Guotao Yang, Yungang Wang, Lianhuan Hu, Dingkun Zhong, Yaxian Li, Yimeng Xu, Min Zhang, Pengfei Hu","doi":"10.1029/2023JA032340","DOIUrl":"https://doi.org/10.1029/2023JA032340","url":null,"abstract":"<p>Solar eclipse traveled across South China in the afternoon on 21 June 2020. Five ionosondes located from mid-to low-latitudes and on both north and south of the eclipse path were applied to investigate the ionospheric responses. Both the zonal and meridional ranges of the observation region have exceeded 1,000 km. All the five ionosondes had observed the Intermediate Descending Layers (IDLs) simultaneously just after the eclipse maximum and this is a very small probability event. During the solar eclipse, the multi-hop echoes above the Es, the rising Es to 150 km altitude, the plasma flux from above F2-layer were also observed and analyzed. The descending trend of the IDLs and the peak height of F2-layer (<i>h</i><sub><i>m</i></sub>F2) shows great consistency, indicating the close relationship between the eclipse induced plasma flux and the IDLs. The traces of gravity waves were also found in the IDLs and F-layer. The plasma flux may carry the ions to valley region and the eclipse produced gravity waves were responsible for the formation of the IDLs.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141584065","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}
When solar wind and interplanetary magnetic field (IMF) disturb, thermospheric winds change accordingly. Among the momentum forces driving high-latitude thermospheric winds, ion drag is supposed to greatly affect wind variations through ion-neutral coupling when abrupt and strong changes in ion drifts occur. However, due to the great inertia of thermospheric winds it needs a certain period of time for the wind changes to be prominent both in speed and direction. How long the neutral winds take to change from one steady state to another through the ion-neutral coupling process is currently still a controversial issue. In this paper, we examine the high latitudinal ion-neutral coupling time scale based on the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations, which can determine whether wind variations are dominantly driven by ion drag by analyzing the relative contribution of each momentum force. It is found that the spatial variation of ion-neutral coupling time scale is primarily determined by local electron density, but also varies with neutral density and ion-neutral collision frequency. Simulations during periods of medium solar activity at ∼250 km altitude show that the ion drag-dominated region is generally located at the dayside convection inverse boundary and the coupling time scale (e-folding time) is ∼1 hr when IMF By is the dominant component of the IMF and changes direction. Meanwhile, the southward component of IMF Bz enlarges the ion drag-dominated region. When IMF Bz is southward with a large magnitude, ion drag-dominated region is primarily located in the nightside auroral oval with ∼2 hr coupling time scale.
当太阳风和行星际磁场(IMF)发生扰动时,热层风也会发生相应的变化。在驱动高纬度热层风的动量中,当离子漂移发生突然而强烈的变化时,离子阻力应该会通过离子-中性耦合对风的变化产生很大影响。然而,由于热层风的巨大惯性,风速和风向的变化都需要一定的时间才能显现出来。中性风通过离子-中性耦合过程从一种稳定状态转变为另一种稳定状态需要多长时间,目前仍是一个有争议的问题。本文基于热层电离层电动力学大气环流模式模拟,研究了高纬度离子-中性风耦合时间尺度,通过分析各动量的相对贡献,确定风的变化是否主要由离子阻力驱动。研究发现,离子-中性耦合时间尺度的空间变化主要由当地电子密度决定,但也随中性密度和离子-中性碰撞频率的变化而变化。在高度为 ∼250 km 的中等太阳活动期间进行的模拟显示,当 IMF By 为 IMF 的主导成分并改变方向时,离子阻力主导区域一般位于日侧对流逆边界,耦合时间尺度(e-折叠时间)为 ∼1 小时。同时,IMF Bz的南向分量扩大了离子阻力主导区域。当IMF Bz南下且幅度较大时,离子阻力主导区主要位于极光椭圆夜侧,耦合时间尺度为∼2小时。
{"title":"A Numerical Study of the High Latitudinal Ion-Neutral Coupling Time Scale Under Disturbed Conditions","authors":"Yusha Tan, Jiuhou Lei, Tong Dang, Wenbin Wang, Binzheng Zhang, Xiaoli Luan, Xiankang Dou","doi":"10.1029/2024JA032497","DOIUrl":"https://doi.org/10.1029/2024JA032497","url":null,"abstract":"<p>When solar wind and interplanetary magnetic field (IMF) disturb, thermospheric winds change accordingly. Among the momentum forces driving high-latitude thermospheric winds, ion drag is supposed to greatly affect wind variations through ion-neutral coupling when abrupt and strong changes in ion drifts occur. However, due to the great inertia of thermospheric winds it needs a certain period of time for the wind changes to be prominent both in speed and direction. How long the neutral winds take to change from one steady state to another through the ion-neutral coupling process is currently still a controversial issue. In this paper, we examine the high latitudinal ion-neutral coupling time scale based on the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations, which can determine whether wind variations are dominantly driven by ion drag by analyzing the relative contribution of each momentum force. It is found that the spatial variation of ion-neutral coupling time scale is primarily determined by local electron density, but also varies with neutral density and ion-neutral collision frequency. Simulations during periods of medium solar activity at ∼250 km altitude show that the ion drag-dominated region is generally located at the dayside convection inverse boundary and the coupling time scale (e-folding time) is ∼1 hr when IMF <i>B</i><sub><i>y</i></sub> is the dominant component of the IMF and changes direction. Meanwhile, the southward component of IMF <i>B</i><sub><i>z</i></sub> enlarges the ion drag-dominated region. When IMF <i>B</i><sub><i>z</i></sub> is southward with a large magnitude, ion drag-dominated region is primarily located in the nightside auroral oval with ∼2 hr coupling time scale.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141565786","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}
C. M. van Hazendonk, L. Baddeley, K. M. Laundal, J. L. Chau
Ultra-low frequency (ULF) waves transfer energy and momentum into the ionosphere-thermosphere system. To quantify this energy, this paper first presents a new method to quantitatively detect ULF waves in Incoherent Scatter Radar (ISR) data based on 2D fast-Fourier transforms and subsequent reconstruction of the wave. In parallel with other data sets, including optical, magnetometer, satellite, and models, we present the first full ionospheric energy dissipation rates for a ULF wave, split into electromagnetic (EM) and kinetic fluxes. The EM energy deposition is calculated from the use of the Poynting theorem, looking at Joule and frictional heating rates, where both rates show the same order of magnitude (1.24 × 1013 and 7.3 × 1012 J) respectively when integrated over the wave lifetime of 2 hr 15 min and an area of 4° magnetic latitude × 74° magnetic longitude. However, contrary to the common assumption that the EM flux is dominant, we determined the kinetic flux, to be almost equal in magnitude (8.7 × 1012 J). This indicates that previous papers might have underestimated the total energy dissipation by ULF waves. Compared to the substorm energy budget, we find that locally, the ULF wave event studied here makes up approximately 10% of a typical substorm cycle budget.
{"title":"Detection and Energy Dissipation of ULF Waves in the Polar Ionosphere: A Case Study Using the EISCAT Radar","authors":"C. M. van Hazendonk, L. Baddeley, K. M. Laundal, J. L. Chau","doi":"10.1029/2024JA032633","DOIUrl":"https://doi.org/10.1029/2024JA032633","url":null,"abstract":"<p>Ultra-low frequency (ULF) waves transfer energy and momentum into the ionosphere-thermosphere system. To quantify this energy, this paper first presents a new method to quantitatively detect ULF waves in Incoherent Scatter Radar (ISR) data based on 2D fast-Fourier transforms and subsequent reconstruction of the wave. In parallel with other data sets, including optical, magnetometer, satellite, and models, we present the first full ionospheric energy dissipation rates for a ULF wave, split into electromagnetic (EM) and kinetic fluxes. The EM energy deposition is calculated from the use of the Poynting theorem, looking at Joule and frictional heating rates, where both rates show the same order of magnitude (1.24 × 10<sup>13</sup> and 7.3 × 10<sup>12</sup> J) respectively when integrated over the wave lifetime of 2 hr 15 min and an area of 4° magnetic latitude × 74° magnetic longitude. However, contrary to the common assumption that the EM flux is dominant, we determined the kinetic flux, to be almost equal in magnitude (8.7 × 10<sup>12</sup> J). This indicates that previous papers might have underestimated the total energy dissipation by ULF waves. Compared to the substorm energy budget, we find that locally, the ULF wave event studied here makes up approximately 10% of a typical substorm cycle budget.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032633","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141583885","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}
Q. Ma, W. Li, X.-J. Zhang, J. Bortnik, X.-C. Shen, A. Daly, W. S. Kurth, B. H. Mauk, F. Allegrini, J. E. P. Connerney, F. Bagenal, S. J. Bolton
Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler-mode waves and relativistic electrons using Juno measurements and wave-particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV at M shell ∼11 near the magnetic equator during perijove-31. The electron injections are related to chorus wave bursts at 0.05–0.5 fce frequencies, where fce is the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90° pitch angle, and the fluxes are high during injections. We calculate the whistler-mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler-mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1–10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave-particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler-mode waves in Jupiter's outer radiation belt.
{"title":"Generation and Impacts of Whistler-Mode Waves During Energetic Electron Injections in Jupiter's Outer Radiation Belt","authors":"Q. Ma, W. Li, X.-J. Zhang, J. Bortnik, X.-C. Shen, A. Daly, W. S. Kurth, B. H. Mauk, F. Allegrini, J. E. P. Connerney, F. Bagenal, S. J. Bolton","doi":"10.1029/2024JA032624","DOIUrl":"https://doi.org/10.1029/2024JA032624","url":null,"abstract":"<p>Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler-mode waves and relativistic electrons using Juno measurements and wave-particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV at <i>M</i> shell ∼11 near the magnetic equator during perijove-31. The electron injections are related to chorus wave bursts at 0.05–0.5 <i>f</i><sub>ce</sub> frequencies, where <i>f</i><sub>ce</sub> is the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90° pitch angle, and the fluxes are high during injections. We calculate the whistler-mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler-mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1–10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave-particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler-mode waves in Jupiter's outer radiation belt.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141565787","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}
Klemens Hocke, Wenyue Wang, Mokhamad Nur Cahyadi, Guanyi Ma
For the first time, characteristics of the geographical and seasonal distribution of the quasi-diurnal lunar O1 tide were derived from a time series of ionospheric total electron content (TEC) maps provided by International Global Navigation Satellite System Service (IGS). The data analysis is focused on solar minimum in 2008 and 2009 where disturbing influences of geomagnetic and solar activity were minimal. We found that the magnitude of the O1 tide is as strong as the “dominant” semidiurnal lunar M2 tide. Relative amplitudes of 10% and larger are observed in some regions for the O1 component in TEC. The O1 component is particularly strong in northern hemispheric winter over the west coast of South America. There, two maxima occur which are northward and southward of the magnetic equator in the Equatorial Ionization Anomaly (EIA) crest regions. Following Yamazaki et al. (2017, https://doi.org/10.1002/2017ja024601), it might be assumed that a longitudinal anomaly of ionospheric conductivities in the Peruvian sector leads to a stronger modulation of the equatorial electrojet by the lunar tides. Electrodynamic lifting of plasma and transport to the EIA crests may explain the variations of the O1 component in TEC. Contrary to many studies, we find the O1 component (period 25.82 hr) more important than the M1 component (period 24.84 hr, a lunar day). We show that the geographical distribution of the O1 component is totally different from that of the M1 component which is smaller. The seasonal variation of O1 shows maximal amplitudes in northern hemispheric winter and minimal amplitudes in southern hemispheric winter.
{"title":"Quasi-Diurnal Lunar Tide O1 in Ionospheric Total Electron Content at Solar Minimum","authors":"Klemens Hocke, Wenyue Wang, Mokhamad Nur Cahyadi, Guanyi Ma","doi":"10.1029/2024JA032834","DOIUrl":"https://doi.org/10.1029/2024JA032834","url":null,"abstract":"<p>For the first time, characteristics of the geographical and seasonal distribution of the quasi-diurnal lunar O<sub>1</sub> tide were derived from a time series of ionospheric total electron content (TEC) maps provided by International Global Navigation Satellite System Service (IGS). The data analysis is focused on solar minimum in 2008 and 2009 where disturbing influences of geomagnetic and solar activity were minimal. We found that the magnitude of the O<sub>1</sub> tide is as strong as the “dominant” semidiurnal lunar M<sub>2</sub> tide. Relative amplitudes of 10% and larger are observed in some regions for the O<sub>1</sub> component in TEC. The O<sub>1</sub> component is particularly strong in northern hemispheric winter over the west coast of South America. There, two maxima occur which are northward and southward of the magnetic equator in the Equatorial Ionization Anomaly (EIA) crest regions. Following Yamazaki et al. (2017, https://doi.org/10.1002/2017ja024601), it might be assumed that a longitudinal anomaly of ionospheric conductivities in the Peruvian sector leads to a stronger modulation of the equatorial electrojet by the lunar tides. Electrodynamic lifting of plasma and transport to the EIA crests may explain the variations of the O<sub>1</sub> component in TEC. Contrary to many studies, we find the O<sub>1</sub> component (period 25.82 hr) more important than the M<sub>1</sub> component (period 24.84 hr, a lunar day). We show that the geographical distribution of the O<sub>1</sub> component is totally different from that of the M<sub>1</sub> component which is smaller. The seasonal variation of O<sub>1</sub> shows maximal amplitudes in northern hemispheric winter and minimal amplitudes in southern hemispheric winter.</p>","PeriodicalId":15894,"journal":{"name":"Journal of Geophysical Research: Space Physics","volume":null,"pages":null},"PeriodicalIF":2.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JA032834","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141583888","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}