We study quasiperiodic very low frequency (VLF) emissions observed simultaneously by Van Allen Probes spacecraft and Kannuslehto and Lovozero ground‐based stations on 25 December 2015. Both Van Allen ...Probes A and B detected quasiperiodic emissions, probably originated from a common source, and observed on the ground. In order to locate possible regions of wave generation, we analyze wave‐normal angles with respect to the geomagnetic field, Poynting flux direction, and cyclotron instability growth rate calculated by using the measured phase space density of energetic electrons. We demonstrate that even parallel wave propagation and proper (downward) Poynting flux direction are not sufficient for claiming observations to be in the source region. Agreement between the growth rate and emission bands was obtained for a restricted part of Van Allen Probe A trajectory corresponding to localized enhancement of plasma density with scale of 700 km. We employ spacecraft density data to build a model plasma profile and to calculate ray trajectories from the point of wave detection in space to the ionosphere and examine the possibility of their propagation toward the ground. For the considered event, the wave could propagate toward the ground in the geomagnetic flux tube with enhanced plasma density, which ensured ducted propagation. The region of wave exit was confirmed by the analysis of wave propagation direction at the ground detection point.
Key Points
Complex analysis of generation region of quasiperiodic VLF emissions were observed simultaneously by two Van Allen Probes and on the ground
Wave growth rate frequency band matched the observed emission band only in a localized (∼0.3 Earth radii) region along Van Allen Probe A trajectory
Ray tracing demonstrated the importance of a density duct for wave propagation toward the ground
We present the results of a multi‐point and multi‐instrument study of electromagnetic ion cyclotron (EMIC) waves and related energetic proton precipitation during a substorm. We analyze the data from ...Arase (ERG) and Van Allen Probes (VAPs) A and B spacecraft for an event of 16 and 17 UT on December 1, 2018. VAP‐A detected an almost dispersionless injection of energetic protons related to the substorm onset in the night sector. Then the proton injection was detected by VAP‐B and further by Arase, as a dispersive enhancement of energetic proton flux. The proton flux enhancement at every spacecraft coincided with the EMIC wave enhancement or appearance. This data show the excitation of EMIC waves first inside an expanding substorm wedge and then by a drifting cloud of injected protons. Low‐orbiting NOAA/POES and MetOp satellites observed precipitation of energetic protons nearly conjugate with the EMIC wave observations in the magnetosphere. The proton pitch‐angle diffusion coefficient and the strong diffusion regime index were calculated based on the observed wave, plasma, and magnetic field parameters. The diffusion coefficient reaches a maximum at energies corresponding well to the energy range of the observed proton precipitation. The diffusion coefficient values indicated the strong diffusion regime, in agreement with the equality of the trapped and precipitating proton flux at the low‐Earth orbit. The growth rate calculations based on the plasma and magnetic field data from both VAP and Arase spacecraft indicated that the detected EMIC waves could be generated in the region of their observation or in its close vicinity.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) waves are believed to play a significant role in the dynamics of energetic protons and relativistic electrons in the Earth's magnetosphere. The properties of these waves are being intensively studied. We consider the conditions of the EMIC wave generation and the dynamics of the wave source during a substorm event using a unique configuration of three spacecraft (Arase and two Van Allen Probes). All spacecraft were at approximately the same distance from the Earth, forming a chain across the evening local time sector. Analyzing parameters of the wave generation obtained from in situ measured proton distribution function, we came to the conclusion that the waves could be generated within the substorm area, sometimes close to, but not necessary at the spacecraft location. As the substorm expands in longitude, the EMIC wave source exhibits a longitudinal drift. When substorm expansion stops, the wave generation region expands due to the magnetic drift of protons injected during the substorm. The observed wave properties show that the waves are able to precipitate energetic protons into the atmosphere. This is confirmed by observations of low orbiting satellites measuring proton precipitating fluxes.
Key Points
Westward propagation of the EMIC wave generation region is due to both the substorm expansion and azimuthal drift of injected protons
Strong pitch‐angle diffusion regime is confirmed by observations of proton fluxes at low altitude and the diffusion coefficient calculation
The diffusion coefficient maximum corresponds well to the energy range of the observed proton precipitation
The occurrence of the magnetic substorms at high geomagnetic latitudes (>70° CGC) has been visually analyzed using the ground-based IMAGE magnetometer chain and OMNI solar wind and Interplanetary ...Magnetic Field (IMF) data. We studied the time intervals closely to the minimum and maximum of the 23-th and 24-th solar cycles. The considered high-latitude substorms have been divided into two different types according to their occurrence relatively to the auroral oval dynamics. The first type - the substorms which expand from the auroral geomagnetic latitudes to the polar ones (named the “expanded” substorms, according to an expanded oval dynamics); the second type - the substorms which are observed only at the geomagnetic latitudes higher ∼ 70° CGC under the absence of simultaneous magnetic disturbances at lower latitudes (named the “polar” substorms, according to a polar latitude contracted oval dynamics). Both substorm types are identified at almost identical latitudes, however, with different latitude of their onset locations. It was found that the “polar” substorms show behavior opposite to the “expanded” ones. The “polar” substorms are observed under a low solar wind speed (V < 500 km/s) and the “expanded” substorms - under a high speed (V > 500 km/s). We found, that the PC-index of the polar cap activity, which could be used as a proxy of changes in solar wind electric field, was lower before the “polar” substorms than before the “expanded” ones. The summer maxima in the seasonal occurrence of the “polar” substorms correspond to the minima of the “expanded” substorm. We did not reveal any significant cycle differences in the distributions of the IMF and solar wind parameters before the both types of substorms observed near the maxima and minima of the 23-th and 24-th cycles of the solar activity.
•The occurrence of the substorms at high geomagnetic latitudes has been analyzed.•substorms were divided into 2 groups: “polar” and “expanded” substorms.•The “polar” substorms behavior was mainly opposite to the “expanded” ones.•These 2 types of substorms appear under different space weather conditions.
Geomagnetic activity and occurrence of large values of geoinduced currents (GICs) during a moderate magnetic storm (SYM/H ∼ −65 nT) on September, 12–13 2017 have been studied. Two intense substorms ...(AL ∼600 nT and ∼1200 nT) were observed within the period of this magnetic storm. Amplification and motion of electrojets during substorms is known to be one of the important sources of GIC value increase in the auroral zone. The fine spatial temporal structure of westward electrojet has been analyzed using the latitudinal profiles of the IMAGE network and the equivalent currents of the MIRACLE system data. GICs activity were monitored by EURISGIC from Russian stations Vykhodnoy (VKH) and Revda (RVD) in the North-West of Russia (eurisgic.ru) and Mäntsälä station (MAN) in South Finland. The data from these stations are convenient to track GIC from ∼60° to ∼69° geographical latitudes. It has been shown that the increase in GIC amplitudes at different latitudes was associated with the poleward movement of the westward electrojet during the expansion phase of the substorm. Besides, it has been found that the source of the GICs at the recovery phase of the second substorm appeared to be a short pulse of Pc5 pulsations and the amplitudes of GICs were comparable with substorms one. It is also shown that the increase in GIC amplitude are in good agreement with the increase in the Wp- and IL-geomagnetic indices used for global and local control over the substorm appearance.
•Geoinduced currents (GICs) during moderate magnetic storm on September 12–13, 2017.•GICs on Vykhodnoy and Revda (North-West of Russia) and Mäntsälä (South of Finland).•GICs at different latitudes match with the expansion of the westward electrojet.•During GICs enhancement IL- and Wp-geomagnetic indexes increase too.•The source of one of the GIC was a short pulses of Pс5 pulsations.
Substorms on a contracted auroral oval Kleimenova, N.G.; Despirak, I.V.; Malysheva, L.M. ...
Journal of atmospheric and solar-terrestrial physics,
April 2023, 2023-04-00, Letnik:
245
Journal Article
Recenzirano
Odprti dostop
The high-latitude magnetic substorms observed at geomagnetic latitudes higher 70° MLAT under the substorm absence at the lower latitudes are known as “substorms on the contracted oval” or “polar” ...substorms. Such substorms appear during quiet or weakly disturbed space weather conditions. The study of 254 “polar” substorms, recorded at the Scandinavian IMAGE magnetometer chain during the winter seasons of 2010–2020, confirmed a tendency to occur in the late evening (∼19–23 MLT), that is a bit earlier than the “normal” substorms (22–24 MLT). It was found that before the onset of “polar” substorms, like “normal” substorms, there is an increase in the PC-index indicating an energy input into the magnetosphere. We established that “polar” substorms, like “normal” substorms, are accompanied by positive mid-latitude magnetic bays, demonstrating a substorm current wedge (SCW) development.
Several “polar” substorms are examined in detail. The ionospheric electrojets and field-aligned currents (FAC) distribution was studied basing on the AMPERE satellites measurements. We found that “polar” substorm onsets are associated with an enhancement of FACs in a localized evening area. Thus, “polar” substorms exhibited the properties, typical for “normal” substorms, so, they could be referred as a specific type of substorms developing under rather quiet space weather conditions.
•High-latitudes magnetic substorms known as “polar” substorms were studied.•IMAGE magnetometers, Barentsburg all-sky camera and AMPERE satellites data were used.•“Polar” substorms are accompanied by the positive mid-latitude bays indicating the SCW develop.•“Polar” substorm appearance is associated with an increasing of field-aligned currents in the evening sector.•PC-index enhancement, associated with an energy input into the magnetosphere, was found prior the substorm onsets.
The spatio-temporal dynamic of the substorm on December 24, 2014 in the interval from 16:00 to 17:00 UT was analyzed by data of large observational complex: magnetometers data by the Scandinavian ...network and by the longitudinal chain of the Russian auroral stations, the auroral dynamics in Apatity and data of THEMIS satellites. During the interval under study the THEMIS-E and THEMIS-D satellites were located in the midnight sector of the magnetosphere at r ~8.5–10.3 RE and then passed over Siberia toward to Kola Peninsula. We show that the first substorm disturbances in the magnetosphere were in the region between the THE and THD satellites, and, according ground-based observations, it was projected to near Amderma station. Despite a sparse observational network in Siberia, the substorm intensification was possible to trace from the point of the origin at the longitude ~80°E to the Scandinavia region at the longitude ~30°E. Our estimates of the propagation velocities of the westward traveling surge (WTS) and so-called “auroral horn” (the arc ahead WTS) confirmed the values, obtained in the previous works. The occurrence of several structures of substorm in aurora (first small, localized auroral arc; beads structure in the auroras and the auroral horn) manifestates the propagation of the disturbances from the onset region to the West. It is shown also, that the fronts of dipolarization (DFs) and injection of energetic electrons in the magnetosphere were accompanied by activations of auroras: the brightening of arcs, the breakup and the appearance of WTS over Apatity.
•Simultaneously observations by the THEMIS, by the aurora and magnetic disturbances.•Analysis of the propagation of the disturbances from the onset region to the West.•Several precursors of substorm in aurora were registered.•Dipolarization fronts and injection of energetic electrons in the magnetosphere.•Simultaneously observations of sudden intensification in aurora.
We examine the effectiveness of nonuniform, quasistatic, transverse electric fields that are often observed in the auroral region in destabilization of inhomogeneous energy-density-driven (IEDD) ...waves. Specifically, the IEDD dispersion relation of Ganguli et al. (1985a, b) is evaluated for an electric field structure observed by the FAST satellite in the auroral ionosphere at 1000 km altitude. The background field-aligned current, plasma density and ion composition are derived from FAST observations. Other input parameters adopted in the calculations are varied in pertinent ranges. Unstable solutions are obtained that indicate a variety of frequencies and perpendicular wavelengths. These can manifest as a broadband spectrum of IEDD waves.
Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H+–He+ plasma of the inner magnetosphere is investigated. The integrated wave gain is obtained by ...integration of a temporal local growth rate along a geomagnetic field line. The local growth rate is determined by the method of Kennel and Petschek (1966) generalized on the case of a bi-ion plasma. The concentration of the cold plasma is obtained on a basis of an empirical model of the plasmasphere and trough by Sheeley et al. (2001). The energetic proton flux in the equatorial inner magnetosphere is set by the empirical model of Milillo et al. (2001), which refers to the conditions of low geomagnetic activity. The coefficients of EMIC wave reflection from the conjugated ionosphere are calculated using the International Reference Ionosphere (IRI) model. It is shown that the integrated wave gain of the EMIC waves increases with L-shell increasing and peaks around 14–20 MLT. In the afternoon sector the integrated wave gain reaches maximum in the cold plasma of higher density. Here the EMIC waves with the frequency below the equatorial He+ gyrofrequency will be generated. The main findings of our study are in agreement with the basic experimental results on the EMIC wave occurrence in the equatorial middle magnetosphere known from satellite observations.
•We calculate the integrated gain of EMIC waves in the H+–He+ plasma.•The integrated wave gain increases with L-shell increase.•The integrated wave gain reaches maximum in the afternoon sector.•The local growth rate can reach maximum outside the equator at latitudes within ±10°.•Our results are in agreement with the results of EMIC wave satellite observations.
A study is performed on the increasing of geomagnetic induced currents (GICs) during supersubstorms (SSS) that occurred on September 7–8, 2017 against the background of magnetic storms. The analysis ...includes two periods: from 23 to 04 UT on September 7–8, 2017 (the first supersubstorm with
SML
~ –3600 nT) and from 12 to 20 UT on September 8, 2017 (the second supersubstorm with
SML
~ –2600 nT and two intense substorms (with
SML
~ –1500 nT). GIC is analyzed using data from detecting stations in Vykhodnoy and Kondopoga (Russia), Mäntsälä (Finland), Halfway Bush (New Zealand), and Torness (Scotland). Results show the GICs developed in a manner similar to that of the substorm westward electrojet’s spatiotemporal dynamics, with maximum GIC values observed at stations in the midnight sector. It is found that there is a relationship between the increasing of the GICs and an increase in geomagnetic indices
IL
and
Wp
that characterize substorm activity.
A study is performed of high-latitude geomagnetic disturbances (MLAT > 70°) that formed during the first magnetic storm of the new solar cycle on April 20, 2020. Measurements by the ground-based ...magnetometers of the SuperMAG, INTERMAGNET, and IMAGE global networks show the geoeffectiveness of the storm was quite high, despite the low speed of the magnetic cloud that caused the storm. High-latitude vortices of the geomagnetic field are identified that could indicate local intensification of the field-aligned currents.
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