PC индекс как показатель энергии солнечного ветра, поступающей в магнитосферу (итоги)

The paper includes a short review of advantages of the PC index which is a characteristic of the magnetic activity in the polar caps in the northern (PCN) and southern (PCS) hemispheres. It is demonstrated that the PC index properly responds to variations of the geoeffective interplanetary electric field E coupling with the magnetosphere, on the one side, and predetermined the development of magnetospheric disturbances (magnetic storms and substorms), on the other side. These experimental results formed the physical backgrounds for concept that the ground-based PC index characterizes the solar wind energy input into the magnetosphere. It is shown that problem of random discordances in behavior and value of the PCN and PCS indices during the summer/winter seasons is easily solved by choosing the PC index in the winter polar cap (PCwinter) as the best characteristic of the polar cap magnetic activity. At present the PC index is successfully applied to validate the utility of SW data presented at OMNI website (i.e. to verify whether or not the solar wind, measured in the Lagrange point, encountered the magnetosphere in reality). A special procedure agreed by the Arctic and Antarctic Research Institute (responsible for production of PCS index) and DTU Space (responsible for production of PCN index) ensures the calculation of the 1-min PC indices in quasi-real time based on data of magnetic observations at the polar cap stations Vostok (Antarctic) and Qaanaaq (Greenland).Дается краткий обзор достижений, полученных при использовании индексов магнитной активности в северной (PCN) и южной (PCS) полярных шапках. Показано, что PC индекс четко отвечает на вариации геоэффективного межпланетного электрического поля E, взаимодействующего с магнитосферой, с одной стороны, и является предвестником магнитосферных возмущений (магнитных бурь и суббурь), с другой стороны. Эти экспериментальные факты послужили основой представления о PC индексе как характеристике энергии солнечного ветра, поступающей в магнитосферу. Показано, что проблема случайных расхождений в поведении и величине PCN и PCS индексов в сезоны зима/лето решается выбором PC индекса в зимней шапке (PCwinter) как наиболее адекватной характеристики магнитной активности. В настоящее время PC индекс успешно применяется при оценке пригодности данных сайта OMNI о параметрах солнечного ветра (т.е. для проверки реальности контакта с магнитосферой солнечного ветра, измеренного в точке либрации). Специальная процедура, согласованная Арктическим и антарктическим НИИ (который ответственен за производство PCS индекса) и Датским техническим университетом (который ответственен за производство PCN индекса), обеспечивает расчет в реальном времени 1-мин PC индекса по данным магнитных наблюдений на полярных станциях Восток (Антарктика) и Туле (Гренландия)

Geosynchronous magnetopause crossings and their relationships with magnetic storms and substorms

The paper investigates the strengthening of magnetospheric activity related to geosynchronous magnetopause crossings (GMCs). We make a list of GMC events using the empirical magnetopause model (Lin et al., 2010) and hourly averaged OMNI data and find which solar wind and magnetospheric conditions accompany and follow the GMCs. The GMCs are mostly caused by the impact of interplanetary coronal mass ejections (ICMEs) and/or interplanetary shocks often with a strong increase in the density and a moderate increase in velocity. The average solar wind density during the first GMC hour is higher than 20 cm−3 in 70 % cases, while the velocity is higher than 500 km/s in 56 % cases. The hourly interplanetary magnetic field (IMF) BZ is negative in 87 % cases. The average over all events SMU (SML), Kp, and PC indices reach maxima (minima) in 1 hour after the GMC beginning, while the delay of the minimum of the Dst index is usually 3–8 hours. These average time delays do not depend on the strength of the storms and substorms. The SML (Dst) minimum is less than -500 nT (-30 nT) in the next 24 hours in 95 % (99 %) cases, i.e. the GMC events are mostly followed by magnetic storms and substorms. We compare solar wind and magnetospheric conditions for GMCs connected with ICMEs and stream interaction regions (SIRs). Our study confirms that the ICME-related events are characterized by stronger ring current and auroral activity than the SIR-related events. The difference might be explained by the different behavior of the solar wind velocity

Remote Detection of Drift Resonance Between Energetic Electrons and Ultralow Frequency Waves: Multisatellite Coordinated Observation by Arase and Van Allen Probes

We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])‐B satellites. On 30 March 2017, both Arase and RBSP‐B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP‐B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP‐B and ground‐magnetometer observations, where Pc5 pulsations are observed to drift‐resonate with relativistic electrons on the duskside. Thus, Arase observed the drift‐resonance signatures “remotely,” whereas RBSP‐B observed them “locally.

Survey of large-amplitude flapping motions in the midtail current sheet

We surveyed fast current sheet crossings (flapping motions) over the distance range 10–30 RE in the magnetotail covered by the Geotail spacecraft. Since the local tilts of these dynamic sheets are large and variable in these events, we compare three different methods of evaluating current sheet normals using 4-s/c Cluster data and define the success criteria for the single-spacecraft-based method (MVA) to obtain the reliable results. Then, after identifying more than ~1100 fast CS crossings over a 3-year period of Geotail observations in 1997–1999, we address their parameters, spatial distribution and activity dependence. We confirm that over the entire distance covered and LT bins, fast crossings have considerable tilts in the YZ plane (from estimated MVA normals) which show a preferential appearance of one (YZ kink-like) mode that is responsible for these severe current sheet perturbations. Their occurrence is highly inhomogeneous; it sharply increases with radial distance and has a peak in the tail center (with some duskward shift), resembling the occurrence of the BBFs, although there is no one-to-one local correspondence between these two phenomena. The crossing durations typically spread around 1 min and decrease significantly where the high-speed flows are registered. Based on an AE index superposed epoch study, the flapping motions prefer to appear during the substorm expansion phase, although a considerable number of events without any electrojet and auroral activity were also observed. We also present statistical distributions of other parameters and briefly discuss what could be possible mechanisms to generate the flapping motions

Superthermal Proton and Electron Fluxes in the Plasma Sheet Transition Region and Their Dependence on Solar Wind Parameters

To study further the factors and mechanisms controlling 10–150 keV particle fluxes in the inner magnetosphere, we investigate empirically their behavior in the nightside transition region (6–14 Re) depending on solar wind parameters taken at different time lags. We aim to establish the hierarchy of predictors (V, N, Pd, Ekl = VByz sin2(θ/2), etc.) and the optimal range of their time delays, both depending on the distance and local time. We use THEMIS 5‐min averaged observations of energetic proton and electron fluxes in 2007–2018 near the plasma sheet midplane and build regression models exploring the combination of predictors, taken at time delays up to 24 h. The model obtained shows that protons and electrons are controlled differently by solar wind parameters: electrons are influenced equally by Vsw and Ekl, whereas protons are controlled mostly by Vsw and Pd and less by Ekl. We found that a wide range of time delays is involved depending on distance and particle energy. Specifically, the Ekl affects the energetic fluxes with time delays up to 24 h (or more), exhibiting the long delays in the innermost regions. As regards the mechanism of Vsw influence, the Vsw‐related flux changes are large and, to a large extent, established on the route of the energy flow from solar wind to the plasma sheet and, eventually, the inner magnetosphere. We also identified a new parameter, NBL = VByz cos2(θ/2), which helps to reveal the loss processes in the plasma sheet transition region.Key PointsMost important predictors of particle flux are Vsw and Ekl for electrons and Vsw and Pd (with smaller impact of Ekl) for protonsEkl time lags depend on energy and distance, with up to 24 h lag (maximum value for present study) in the region closest to EarthSolar wind velocity controls the energetic population in the tail plasma sheetPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167082/1/jgra56326_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167082/2/jgra56326.pd

Superthermal Proton and Electron Fluxes in the Plasma Sheet Transition Region and Their Dependence on Solar Wind Parameters

To study further the factors and mechanisms controlling 10–150 keV particle fluxes in the inner magnetosphere, we investigate empirically their behavior in the nightside transition region (6–14 Re) depending on solar wind parameters taken at different time lags. We aim to establish the hierarchy of predictors (V, N, Pd, Ekl = VByz sin2(θ/2), etc.) and the optimal range of their time delays, both depending on the distance and local time. We use THEMIS 5‐min averaged observations of energetic proton and electron fluxes in 2007–2018 near the plasma sheet midplane and build regression models exploring the combination of predictors, taken at time delays up to 24 h. The model obtained shows that protons and electrons are controlled differently by solar wind parameters: electrons are influenced equally by Vsw and Ekl, whereas protons are controlled mostly by Vsw and Pd and less by Ekl. We found that a wide range of time delays is involved depending on distance and particle energy. Specifically, the Ekl affects the energetic fluxes with time delays up to 24 h (or more), exhibiting the long delays in the innermost regions. As regards the mechanism of Vsw influence, the Vsw‐related flux changes are large and, to a large extent, established on the route of the energy flow from solar wind to the plasma sheet and, eventually, the inner magnetosphere. We also identified a new parameter, NBL = VByz cos2(θ/2), which helps to reveal the loss processes in the plasma sheet transition region.Key PointsMost important predictors of particle flux are Vsw and Ekl for electrons and Vsw and Pd (with smaller impact of Ekl) for protonsEkl time lags depend on energy and distance, with up to 24 h lag (maximum value for present study) in the region closest to EarthSolar wind velocity controls the energetic population in the tail plasma sheetPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167082/1/jgra56326_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167082/2/jgra56326.pd

Driftâ Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations

A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L ~5.4â 6.1) near postmidnight (Lâ magnetic local time ~1.8â 2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (mâ number) is estimated using two independent methods with satellites and ground observations to be â 8 to â 15. The direct measurement of the mâ number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at ⠥ 56.3 keV are caused by drift resonance and those of O+ ions at ⠤ 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at ⠤ 18.6 keV indicates selective acceleration of O+ ions through bounce resonance.Plain Language SummaryGeomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150â 600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at ⠥ 56.3 keV and the O+ ion fluxes at ⠤ 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at ⠤ 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances.Key PointsA largeâ amplitude Pc5 wave is observed by Arase and MMS1 in the postmidnight region at L > 5.4 during the storm recovery phaseWe estimate the mâ number of the Pc5 wave to be â 8 to â 15 by using two independent methods with satellites and ground observationsWe simultaneously observe the drift resonance for H+ and O+ ions at ⠥ 56.3 keV and bounce resonance for O+ ions at ⠤ 18.6 keVPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145558/1/grl57758_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145558/2/grl57758.pd