Bibliography
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Found 40 entries in the Bibliography.
Showing entries from 1 through 40
| 2021 |
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A Statistical Study of Low-Energy Ion Flux Enhancements by EMIC Waves in the Inner Magnetosphere Abstract We have studied the statistical properties of low-energy proton (H+) and helium (He+) ion flux enhancements associated with EMIC waves in the inner magnetosphere using Van Allen Probes data for 2013-2017. We identified 167 low-energy ion flux enhancements when the EMIC waves occurred in a He-band or in a multiple band (H-band and He-band) with strong He-band and weak H-band wave activity and found that most of them occurred from the noon to the premidnight sector near the magnetic equator just inside the plasmapause. Of 167 flux enhancement events, 68 exhibited only He+ flux enhancements, and 99 exhibited both H+ and He+ flux enhancements. The EMIC wave-associated flux enhancement events are mostly energized in the direction perpendicular to the background magnetic field. When both H+ and He+ fluxes are simultaneously enhanced, the H+ flux events have a peak energy distributed in the range of 2-100 eV, and the peak energies of the He+ flux events are distributed in the 2 eV to 600 eV range, implying that the helium ions are more energized than the protons. The peak energies of only He+ flux enhancement without H+ flux enhancement are mostly distributed in a lower energy range, 2-10 eV. The energization of H+ and He+ ions can be explained by a linear plasma flow associated with EMIC waves. We suggest that the wave-associated linear plasma motion is a likely mechanism to explain the observations. This article is protected by copyright. All rights reserved. Lee, Junhyun; Kim, Khan-Hyuk; Lee, Ensang; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029793 |
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Evening side EMIC waves and related proton precipitation induced by a substorm Abstract We present the results of a multi-point and multi-instrument study of EMIC waves and related energetic proton precipitation during a substorm. We analyze the data from Arase (ERG) and Van Allen Probes (VAP) A and B spacecraft for an event of 16-17 UT on 01 December 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 shows 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. Yahnin, A.; Popova, T.; Demekhov, A.; Lubchich, A.; Matsuoka, A.; Asamura, K.; Miyoshi, Y.; Yokota, S.; Kasahara, S.; Keika, K.; Hori, T.; Tsuchiya, F.; Kumamoto, A.; Kasahara, Y.; Shoji, M.; Kasaba, Y.; Nakamura, S.; Shinohara, I.; Kim, H.; Noh, S.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029091 |
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Rapid injections of MeV electrons and extremely fast step-like outer radiation belt enhancements Abstract Rapid injection of MeV electrons associated with strong substorm dipolarization has been suggested as a potential explanation for some radiation belt enhancement events. However, it has been difficult to quantify the contribution of MeV electron injections to radiation belt enhancements. This paper presents two isolated MeV electron injection events for which we quite precisely quantify how the entire outer-belt immediately changed with the injections. Tracking detailed outer-belt evolution observed by Van Allen Probes, for both events, we identify large step-like relativistic electron enhancements (roughly 1-order of magnitude increase for ∼2 MeV electron fluxes) for L ≳ 3.8 and L ≳ 4.6, respectively, that occurred on ∼30-min timescales nearly instantaneously with the injections. The enhancements occurred almost simultaneously for 10s keV to multi-MeV electrons, with the lowest-L of enhancement region located farther out for higher energy. The outer-belt stayed at these new levels for ≳ several hours without substantial subsequent enhancements. Kim, H.-J.; Lee, D.-Y.; Wolf, R.; Bortnik, J.; Kim, K.-C.; Lyons, L.; Choe, W.; Noh, S.-J.; Choi, K.-E.; Yue, C.; Li, J.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093151 Radiation belt enhancement; Relatvistic electrons; substorm injection; Step-like; Extremely fast; Van Allen Probes |
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Rapid injections of MeV electrons and extremely fast step-like outer radiation belt enhancements Abstract Rapid injection of MeV electrons associated with strong substorm dipolarization has been suggested as a potential explanation for some radiation belt enhancement events. However, it has been difficult to quantify the contribution of MeV electron injections to radiation belt enhancements. This paper presents two isolated MeV electron injection events for which we quite precisely quantify how the entire outer-belt immediately changed with the injections. Tracking detailed outer-belt evolution observed by Van Allen Probes, for both events, we identify large step-like relativistic electron enhancements (roughly 1-order of magnitude increase for ∼2 MeV electron fluxes) for L ≳ 3.8 and L ≳ 4.6, respectively, that occurred on ∼30-min timescales nearly instantaneously with the injections. The enhancements occurred almost simultaneously for 10s keV to multi-MeV electrons, with the lowest-L of enhancement region located farther out for higher energy. The outer-belt stayed at these new levels for ≳ several hours without substantial subsequent enhancements. Kim, H.-J.; Lee, D.-Y.; Wolf, R.; Bortnik, J.; Kim, K.-C.; Lyons, L.; Choe, W.; Noh, S.-J.; Choi, K.-E.; Yue, C.; Li, J.; Published by: Geophysical Research Letters Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021GL093151 Radiation belt enhancement; Relatvistic electrons; substorm injection; Step-like; Extremely fast; Van Allen Probes |
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Upper limit of proton anisotropy and its relation to EMIC waves in the inner magnetosphere Abstract Proton anisotropy in velocity space has been generally accepted as a major parameter for exciting electromagnetic ion cyclotron (EMIC) waves. In this study, we estimate the proton anisotropy parameter as defined by the linear resonance theory using data from the Van Allen Probes mission. Our investigation uses the measurements of the inner magnetosphere (L < 6) from January 2013 to February 2018. We find that the proton anisotropy is always clearly limited by an upper bound and it well follows an inverse relationship with the parallel proton β (the ratio of the plasma pressure to the magnetic pressure) within a certain range. This upper bound exists over wide spatial regions, AE conditions, and resonance energies regardless of the presence of EMIC waves. EMIC waves occur when the anisotropy lies below but close to this upper bound within a narrow plasma β range: The lower cutoff β is due to an excessively high anisotropy threshold and the upper cutoff β is possibly due to the predominant role of a faster-growing mirror mode instability. We also find that the anisotropy during the observed EMIC waves is unstable, leading to the linear ion cyclotron instability. This result implies that the upper bound of the anisotropy is due to nonlinear processes. This article is protected by copyright. All rights reserved. Noh, Sung-Jun; Lee, Dae-Young; Kim, Hyomin; Lanzerotti, Louis; Gerrard, Andrew; Skoug, Ruth; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028614 Proton Anisotropy; Ion cyclotron instability; Proton distribution; Van Allen Probes; Wave-particle interaction |
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A Case Study of Transversely Heated Low-Energy Helium Ions by EMIC Waves in the Plasmasphere Abstract The Van Allen Probe A spacecraft observed strong ∼0.5-Hz helium (He+) band and weak ∼0.8-Hz hydrogen (H+) band EMIC waves on April 17, 2018, at L = ∼4.5–5.2, in the dawn sector, near the magnetic equator, and close to the plasmapause. We examined low-energy ion fluxes observed by the Helium Oxygen Proton and Electron (HOPE) instrument onboard Van Allen Probe A during the wave interval and found that low-energy He+ flux (<10 eV) enhancements occur nearly simultaneously with He-band and H-band EMIC wave power enhancements in a direction mostly perpendicular to the background magnetic field without significant low-energy H+ and O+ flux variations. We suggest that cold He+ ions (<1 eV) are preferentially and transversely heated up 10 eV through the interaction with EMIC waves inside the plasmasphere. The low-Earth orbit spacecraft observed localized precipitations of energetic protons in the upper ionosphere at subauroral latitudes near the magnetic field footprint of Van Allen Probe A. Our observations provide a clear evidence that EMIC waves play an important role in the overall dynamics in the inner magnetosphere, contributing to the high-energy particle loss and low-energy particle energization. Kim, Khan-Hyuk; Kwon, Hyuck-Jin; Lee, Junhyun; Jin, Ho; Seough, Jungjoon; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028560 |
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Observations of Particle Loss due to Injection-Associated EMIC Waves AbstractWe report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5 − 6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density (PSD) profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt. Kim, Hyomin; Schiller, Quintin; Engebretson, Mark; Noh, Sungjun; Kuzichev, Ilya; Lanzerotti, Louis; Gerrard, Andrew; Kim, Khan-Hyuk; Lessard, Marc; Spence, Harlan; Lee, Dae-Young; Matzka, Jürgen; Fromm, Tanja; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028503 EMIC waves; ring current; Radiation belt; wave particle interaction; injection; Particle precipitation; Van Allen Probes |
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Observations of Particle Loss due to Injection-Associated EMIC Waves AbstractWe report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5 − 6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density (PSD) profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt. Kim, Hyomin; Schiller, Quintin; Engebretson, Mark; Noh, Sungjun; Kuzichev, Ilya; Lanzerotti, Louis; Gerrard, Andrew; Kim, Khan-Hyuk; Lessard, Marc; Spence, Harlan; Lee, Dae-Young; Matzka, Jürgen; Fromm, Tanja; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA028503 EMIC waves; ring current; Radiation belt; wave particle interaction; injection; Particle precipitation; Van Allen Probes |
| 2020 |
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Results from the NASA Van Allen Probes mission indicate extensive observations of mirror/drift-mirror (M/D-M hereafter) unstable plasma regions in the nightside inner magnetosphere. Said plasmas lie on the threshold between the kinetic and frozen-in plasma regimes and have favorable conditions for the formation of M/D-M modes and subsequent ultra-low frequency (ULF) wave signatures in the surrounding plasma. We present the results of a climatological analysis of plasma-γ (anisotropy measure) and total plasma-β (ratio of particle to magnetic field pressure) in regard to the satisfaction of instability conditions on said M/D-M modes under bi-Maxwellian distribution assumption, and ascertain the most likely region for such plasmas to occur. Our results indicate a strong preference for the pre-midnight sector of the nightside magnetosphere, with events ranging in time scales from half a minute (roughly 200 km in scale size) to several hours (multiple Earth radii). The statistical distribution of these plasma regions explicitly identifies the source region of “storm time Pc5 ULF waves” and suggests an alternative mechanism for their generation in the nightside inner magnetosphere. Cooper, M.; Gerrard, A.; Lanzerotti, L.; Soto-Chavez, A.; Kim, H.; Kuzichev, I.; Goodwin, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028773 Mirror mode-unstable plasma; ULF waves; magnetotail injections; inner magnetosphere; Van Allen Probes |
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Quantifying the Effect of Plasmaspheric Hiss on the Electron Loss from the Slot Region Abstract We present global statistical models of both wave amplitude and wave normal angle (WNA) of plasmaspheric hiss using Van Allen Probe-A observations. They utilize the time history of solar wind parameters, i.e., interplanetary magnetic field BZ and solar wind speed, and the AE index for each measurement of hiss waves as inputs. The solar wind parameter-based model generally results in higher performance than using only the AE index as an input. Both observations and model results reveal a clear dependence of hiss wave distribution on the magnetic local time (MLT): higher amplitudes with field-aligned (<30o) WNAs occur more frequently on the dayside than on the nightside. Such a tendency does not depend on magnetic latitude (MLAT), but slightly larger WNAs with a relatively low amplitude frequently appear for larger MLAT (>10o). We also examine how significantly the electron loss rates in the slot region can be changed by incorporating the model output of hiss waves into a diffusive transport simulation. Simulation results show that during a typical timescale (roughly a couple of days) of a corotating interaction region-driven storm, the nightside hiss waves with larger WNA (>30o) do not contribute to the electron loss in the slot region due to their low amplitude and large WNA, while dayside hiss with WNAs less than 30o and comparatively higher amplitudes leads to a fast drop in flux, especially for electrons of a few hundred keV. Kim, Kyung-Chan; Shprits, Yuri; Wang, Dedong; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027555 Plasmaspheric Hiss; Van Allen Probes; Electron slot region; Statistical modeling; Diffusion simulation; Wave-particle interaction |
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Quantifying the Effect of Plasmaspheric Hiss on the Electron Loss From the Slot Region We present global statistical models of both wave amplitude and wave normal angle (WNA) of plasmaspheric hiss using Van Allen Probe-A observations. They utilize the time history of solar wind parameters, that is, interplanetary magnetic field BZ and solar wind speed, and the AE index for each measurement of hiss waves as inputs. The solar wind parameter-based model generally results in higher performance than using only the AE index as an input. Both observations and model results reveal a clear dependence of hiss wave distribution on the magnetic local time (MLT): Higher amplitudes with field-aligned (<30o) WNAs occur more frequently on the dayside than on the nightside. Such a tendency does not depend on magnetic latitude (MLAT), but slightly larger WNAs with a relatively low amplitude frequently appear for larger MLAT (>10o). We also examine how significantly the electron loss rates in the slot region can be changed by incorporating the model output of hiss waves into a diffusive transport simulation. Simulation results show that during a typical timescale (roughly a couple of days) of a corotating interaction region-driven storm, the nightside hiss waves with larger WNA (>30o) do not contribute to the electron loss in the slot region due to their low amplitude and large WNA, while dayside hiss with WNAs less than 30o and comparatively higher amplitudes leads to a fast drop in flux, especially for electrons of a few hundred keV. Kim, Kyung-Chan; Shprits, Yuri; Wang, Dedong; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027555 Plasmaspheric Hiss; Van Allen Probes; Electron slot region; Statistical modeling; Diffusion simulation; Wave-particle interaction |
| 2019 |
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We report on evidence for the generation of an ultra-low frequency plasma wave by the drift-mirror plasma instability in the dynamic plasma environment of Earth\textquoterights inner magnetosphere. The plasma measurements are obtained from the Radiation Belt Storm Probes Ion Composition Experiment onboard NASA\textquoterights Van Allen Probes Satellites. We show that the measured wave-particle interactions are driven by the drift-mirror instability. Theoretical analysis of the data demonstrates that the drift-mirror mode plasma instability condition is well satisfied. We also demonstrate, for the first time, that the measured wave growth rate agrees well with the predicted linear theory growth rate. Hence, the in-situ space plasma observations and theoretical analysis demonstrate that local generation of ultra-low frequency and high amplitude plasma waves can occur in the high beta plasma conditions of Earth\textquoterights inner magnetosphere. Soto-Chavez, A.; Lanzerotti, L.; Manweiler, J.; Gerrard, A.; Cohen, R.; Xia, Z.; Chen, L.; Kim, H.; Published by: Physics of Plasmas Published on: 04/2019 YEAR: 2019 DOI: 10.1063/1.5083629 |
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Quasi Thermal Noise Spectroscopy for Van Allen Probes Quasi thermal fluctuations in the Langmuir/upper-hybrid frequency range are pervasively observed in space plasmas including the radiation belt and the ring current region of inner magnetosphere as well as the solar wind. The quasi thermal noise spectroscopy may be employed in order to determine the electron density and temperature as well as to diagnose the properties of energetic electrons when direct measurements are not available. However, when employing the technique, one must carefully take the spacecraft orientation into account. The present paper takes the upper-hybrid and multiple harmonic\textemdashor (n + 1/2)fce\textemdashemissions measured by the Van Allen Probes as an example in order to illustrate how the spacecraft antenna geometrical factor can be incorporated into the theoretical interpretation. This method can in principle be applied to other spacecraft, including the Parker Solar Probe. Yoon, Peter; Hwang, Junga; Kim, Hyangpyo; Seough, Jungjoon; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019JA026460 (n+1/2)fce; antenna geometry; Quasi-thermal; Radiation belt; Upper hybrid; Van Allen Probes |
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Statistical Analysis of Hiss Waves in Plasmaspheric Plumes Using Van Allen Probe Observations Plasmaspheric hiss waves commonly observed in high-density regions in the Earth\textquoterights magnetosphere are known to be one of the main contributors to the loss of radiation belt electrons. There has been a lot of effort to investigate the distributions of hiss waves in the plasmasphere, while relatively little attention has been given to those in the plasmaspheric plume. In this study, we present for the first time a statistical analysis of the occurrence and the spatial distribution of wave amplitudes and wave normal angles for hiss waves in plumes using Van Allen Probes observations during the period of October 2012 to December 2016. Statistical results show that a wide range of hiss wave amplitudes in plumes from a few picotesla to >100 pT is observed, but a modest (<20 pT) wave amplitude is more commonly observed regardless of geomagnetic activity in both the midnight-to-dawn and dusk sector. By contrast, stronger amplitude hiss occurs preferentially during geomagnetically active times in the dusk sector. The wave normal angles are distributed over a broad range from 0\textdegree to 90\textdegree with a bimodal distribution: a quasi-field-aligned population (<20\textdegree) with an occurrence rate of <60\% and an oblique one (>50\textdegree) with a relative low occurrence rate of ≲20\%. Therefore, from a statistical point of view, we confirm that the hiss intensity (a few tens of picotesla) and field-aligned hiss wave adopted in previous simulation studies are a reasonable assumption but stress that the activity dependence of the wave amplitude should be considered. Kim, Kyung-Chan; Shprits, Yuri; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026458 |
| 2018 |
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The stimulation of EMIC waves by a magnetospheric compression is perhaps the closest thing to a controlled experiment that is currently possible in magnetospheric physics, in that one prominent factor that can increase wave growth acts at a well-defined time. We present a detailed analysis of EMIC waves observed in the outer dayside magnetosphere by the four Magnetosphere Multiscale (MMS) spacecraft, Van Allen Probe A, and GOES 13, and by four very high latitude ground magnetometer stations in the western hemisphere before, during, and after a modest interplanetary shock on December 14, 2015. Analysis shows several features consistent with current theory, as well as some unexpected features. During the most intense MMS wave burst, which began ~ 1 min after the end of a brief magnetosheath incursion, independent transverse EMIC waves with orthogonal linear polarizations appeared simultaneously at all four spacecraft. He++ band EMIC waves were observed by MMS inside the magnetosphere, whereas almost all previous studies of He++ band EMIC waves observed them only in the magnetosheath and magnetopause boundary layers. Transverse EMIC waves also appeared at Van Allen Probe A and GOES 13 very near the times when the magnetic field compression reached their locations, indicating that the compression lowered the instability threshold to allow for EMIC wave generation throughout the outer dayside magnetosphere. The timing of the EMIC waves at both MMS and Van Allen Probe A was consistent with theoretical expectations for EMIC instabilities based on characteristics of the proton distributions observed by instruments on these spacecraft. Engebretson, M.; Posch, J.; Capman, N.; Campuzano, N.; elik, P.; Allen, R.; Vines, S.; Anderson, B.; Tian, S.; Cattell, C.; Wygant, J.; Fuselier, S.; Argall, M.; Lessard, M.; Torbert, R.; Moldwin, M.; Hartinger, M.; Kim, H.; Russell, C.; Kletzing, C.; Reeves, G.; Singer, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025984 |
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Anisotropic velocity distributions of protons have long been considered as free energy sources for exciting electromagnetic ion cyclotron (EMIC) waves in the Earth\textquoterights magnetosphere. Here we rigorously calculated the proton anisotropy parameter using proton data obtained from Van Allen Probe-A observations. The calculations are performed for times during EMIC wave events (distinguishing the times immediately after and before EMIC wave onsets) and for times exhibiting no EMIC waves. We find that the anisotropy values are often larger immediately after EMIC wave onsets than the times just before EMIC wave onsets and the non-EMIC wave times. The increase in anisotropy immediately after the EMIC wave onsets is rather small but discernible, such that the average increase is by ~15\% relative to the anisotropy values during the non-EMIC wave times and ~8\% compared to those just before the EMIC wave onsets. Based on the calculated anisotropy values, we test the criterion for ion cyclotron instability suggested by Kennel and Petschek (1966, https://doi.org/10.1029/JZ071i001p00001) by applying it to the EMIC wave events. We find that despite the weak increase in anisotropy, the majority of the EMIC wave events satisfy the instability criterion. We suggest that the proton distributions often remain close to the marginal state to ion cyclotron instability, and consequently, the proton anisotropy values should often be observed near threshold values for ion cyclotron instability. Additionally, we demonstrate the usefulness and limitation of the instability criteria expressed in the form of an inverse relation between the anisotropy and plasma beta. Noh, Sung-Jun; Lee, Dae-Young; Choi, Cheong-Rim; Kim, Hyomin; Skoug, Ruth; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018JA025385 EMIC waves; Ion cyclotron instability; RBSP; temperature anisotropy; Van Allen Probes |
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Characteristics of Sudden Commencements Observed by Van Allen Probes in the Inner Magnetosphere We have statistically studied sudden commencement (SC) by using the data acquired from Van Allen Probes (VAP) in the inner magnetosphere (L = 3.0\textendash6.5) and GOES spacecraft at geosynchronous orbit (L =\~ 6.7) from October 2012 to September 2017. During the time period, we identified 85 SCs in the inner magnetosphere and 90 SCs at geosynchronous orbit. Statistical results of the SC events reveal the following characteristics. (1) There is strong seasonal dependence of the geosynchronous SC amplitude in the radial BV component at all local times. However, BV shows weak seasonal variation on the dayside in the inner magnetosphere. (2) The local time dependence of the SC amplitude in the compressional BH component at geosynchronous orbit is similar to that in the inner magnetosphere. (3) In a nightside region of L = 5.0\textendash6.5, \~19\% of BH events are negative, while \~58\% of BH events are negative at geosynchronous orbit. (4) The amplitude of the SC-associated Ey perturbations varies systematically with local time with a morning-afternoon asymmetry near noon. These observations can be explained by spatial and/or temporal changes in the magnetopause and cross-tail currents, which are caused by changes in the solar wind dynamic pressure, with respect to spacecraft positions. Fathy, A.; Kim, K.-H.; Park, J.-S.; Jin, H.; Kletzing, C.; Wygant, J.; Ghamry, E.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2018 YEAR: 2018 DOI: 10.1002/2017JA024770 |
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Space Weather Operation at KASI with Van Allen Probes Beacon Signals The Van Allen Probes (VAPs) are the only modern NASA spacecraft broadcasting real-time data on the Earth\textquoterights radiation belts for space weather operations. Since 2012, the Korea Astronomy and Space Science Institute (KASI) has contributed to the receipt of this data via a 7-m satellite tracking antenna and used these data for space weather operations. An approximately 15-min period is required from measurement to acquisition of Level-1 data. In this paper, we demonstrate the use of VAP data for monitoring space weather conditions at geostationary orbit (GEO) by highlighting the Saint Patrick\textquoterights Day storm of 2015. During that storm, Probe-A observed a significant increase in the relativistic electron flux at 3 RE. Those electrons diffused outward resulting in a large increase of the electron flux > 2 MeV at GEO, which potentially threatened satellite operations. Based on this study, we conclude that the combination of VAP data and National Oceanic and Atmospheric Administration-Geostationary Operational Environmental Satellite (NOAA-GOES) data can provide improved space environment information to geostationary satellite operators. In addition, the findings obtained indicate that more data-receiving sites would be necessary and data connections improved if this or a similar system were to be used as an operational data service. Lee, Jongkil; Kim, Kyung-Chan; Romeo, Giuseppe; Ukhorskiy, Sasha; Sibeck, David; Kessel, Ramona; Mauk, Barry; Giles, Barbara; Gu, Bon-Jun; Lee, Hyesook; Park, Young-Deuk; Lee, Jaejin; Published by: Space Weather Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017SW001726 Electron acceleration; Radiation belt; Relativistic electron; Space weather; Van Allen Probes |
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Survey of the Favorable Conditions for Magnetosonic Wave Excitation The ratio of the proton ring velocity (VR) to the local Alfven speed (VA), in addition to proton ring distributions, plays a key factor in the excitation of magnetosonic waves at frequencies between the proton cyclotron frequency fcp and the lower hybrid resonance frequency fLHR in the Earth\textquoterights magnetosphere. Here we investigate whether there is a statistically significant relationship between occurrences of proton rings and magnetosonic waves both outside and inside the plasmapause using particle and wave data from Van Allen Probe-A during the time period of October 2012 to December 2015. We also perform a statistical survey of the ratio of the ring energy (ER, corresponding to VR) to the Alfven energy (EA, corresponding to VA) to determine the favorable conditions under which magnetosonic waves in each of two frequency bands (fcp < f <= 0.5 fLHR and 0.5 fLHR < f < fLHR) can be excited. The results show that the magnetosonic waves in both frequency bands occur around the postnoon (12\textendash18 magnetic local time, MLT) sector outside the plasmapause when ER is comparable to or lower than EA, and those in lower-frequency bands (fcp < f <= 0.5 fLHR) occur around the postnoon sector inside the plasmapause when ER/EA > ~9. However, there is one discrepancy between occurrences of proton rings and magnetosonic waves in low-frequency bands around the prenoon sector (6\textendash12 MLT) outside the plasmapause, which suggests either that the waves may have propagated during active time from the postnoon sector after being excited during quiet time, or they may have locally excited in the prenoon sector during active time. Kim, Kyung-Chan; Shprits, Yuri; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017JA024865 magnetosonic equatorial noise; proton ring distribution; Van Allen Probes |
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Van Allen Probes Observations of Second Harmonic Poloidal Standing Alfv\ en Waves Long-lasting second-harmonic poloidal standing Alfv\ en waves (P2 waves) were observed by the twin Van Allen Probes (Radiation Belt Storm Probes, or RBSP) spacecraft in the noon sector of the plasmasphere, when the spacecraft were close to the magnetic equator and had a small azimuthal separation. Oscillations of proton fluxes at the wave frequency (\~10 mHz) were also observed in the energy (W) range 50\textendash300 keV. Using the unique RBSP orbital configuration, we determined the phase delay of magnetic field perturbations between the spacecraft with a 2nπ ambiguity. We then used finite gyroradius effects seen in the proton flux oscillations to remove the ambiguity and found that the waves were propagating westward with an azimuthal wave number (m) of \~-200. The phase of the proton flux oscillations relative to the radial component of the wave magnetic field progresses with W, crossing 0 (northward moving protons) or 180\textdegree (southward moving protons) at W \~ 120 keV. This feature is explained by drift-bounce resonance (mωd \~ ωb) of \~120 keV protons with the waves, where ωd and ωb are the proton drift and bounce frequencies. At lower energies, the proton phase space density ( math formula) exhibits a bump-on-tail structure with math formula occurring in the 1\textendash10 keV energy range. This math formula is unstable and can excite P2 waves through bounce resonance (ω \~ ωb), where ω is the wave frequency. Takahashi, Kazue; Oimatsu, Satoshi; e, Masahito; Min, Kyungguk; Claudepierre, Seth; Chan, Anthony; Wygant, John; Kim, Hyomin; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017JA024869 bounce and drift-bounce resonances; energetic protons; plasmasphere; poloidal ULF waves; second harmonic; Van Allen Probes |
| 2017 |
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SC-associated electric field variations in the magnetosphere and ionospheric convective flows We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth\textquoterights magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at THEMIS-E (THE-E: MLT = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L= 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E-field perturbation around midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and weaker than that at THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause. Kim, S.-I.; Kim, K.-H.; Kwon, H.-J.; Jin, H.; Lee, E.; Jee, G.; Nishitani, N.; Hori, T.; Lester, M.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024611 |
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SC-associated electric field variations in the magnetosphere and ionospheric convective flows We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth\textquoterights magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at THEMIS-E (THE-E: MLT = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L= 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E-field perturbation around midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and weaker than that at THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause. Kim, S.-I.; Kim, K.-H.; Kwon, H.-J.; Jin, H.; Lee, E.; Jee, G.; Nishitani, N.; Hori, T.; Lester, M.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024611 |
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Ring Current He-Ion Control by Bounce Resonant ULF Waves Ring current energy He-ion (\~65 keV to \~520 keV) differential flux data from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft show considerable variability during quiet solar wind and geomagnetic time periods. Such variability is apparent from orbit to orbit (\~9 hours) of the spacecraft and is observed to be \~50\textendash100\% of the nominal flux. Using data from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument, also aboard the Van Allen Probes spacecraft, we identify that a dominant source of this variability is from ULF waveforms with periods of 10\textquoterights of sec. These periods correspond to the bounce resonant timescales of the ring current He-ions being measured by RBSPICE. A statistical survey using the particle and field data for one full spacecraft precession period (approximately two years) shows that the wave and He-ion flux variations are generally anti-correlated, suggesting the bounce resonant pitch-angle scattering process as a major component in the scattering of He-ions. Kim, Hyomin; Gerrard, Andrew; Lanzerotti, Louis; Soto-Chavez, Rualdo; Cohen, Ross; Manweiler, Jerry; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA023958 bounce resonance; Helium ion; ring current; ULF waves; Van Allen Probes |
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In this paper, using the multisatellite (the Van Allen Probes and two GOES satellites) observations in the inner magnetosphere, we examine two electromagnetic ion cyclotron (EMIC) wave events that are triggered by Pdyn enhancements under prolonged northward interplanetary magnetic field quiet time preconditions. For both events, the impact of enhanced Pdyn causes EMIC waves at multiple points. However, we find a strong spatial dependence that EMIC waves due to enhanced Pdyn impact can occur at multiple points (likely globally but not necessarily everywhere) but with different wave properties. For Event 1, three satellites situated at a nearly same dawnside zone but at slightly different L shells see occurrence of EMIC waves but in different frequencies relative to local ion gyrofrequencies and with different polarizations. These waves are found inside or at the outer edge of the plasmasphere. Another satellite near noon observes no dramatic EMIC wave despite the strongest magnetic compression there. For Event 2, the four satellites are situated at widely separated magnetic local time zones when they see occurrence of EMIC waves. They are again found at different frequencies relative to local ion gyrofrequencies with different polarizations and all outside the plasmasphere. We propose two possible explanations that (i) if triggered by enhanced Pdyn impact, details of ion cyclotron instability growth can be sensitive to local plasma conditions related to background proton distributions, and (ii) there can be preexisting waves with a specific spatial distribution, which determines occurrence and specific properties of EMIC waves depending on satellite\textquoterights relative position after an enhanced Pdyn arrives. Cho, J.-H.; Lee, D.-Y.; Noh, S.-J.; Kim, H.; Choi, C.; Lee, J.; Hwang, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2017 YEAR: 2017 DOI: 10.1002/2016JA023827 |
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We present the dependence of the magnetosonic wave amplitudes both outside and inside the plasmapause on the solar wind and AE index using Van Allen Probe-A spacecraft during the time period of 1 October 2012 to 31 December 2015, based on a correlation and regression analysis. Solar wind parameters considered are the southward interplanetary magnetic field (IMF BS), solar wind number density (NSW), and bulk speed (VSW). We find that the wave amplitudes outside (inside) the plasmapause are well correlated with the preceding AE, IMF BS, and NSW with time delays, each corresponding to 2\textendash3 h (3\textendash4 h), 4\textendash5 h (3\textendash4 h), and 2\textendash3 h (8\textendash9 h), while the correlation with VSW is ambiguous both inside and outside the plasmapause. As measured by the correlation coefficient, the IMF BS is the most influential solar wind parameter that affects the dayside wave amplitudes both outside and inside the plasmapause, while NSW contributes to enhancing the duskside waves outside the plasmapause. The AE effect on wave amplitudes is comparable to that of IMF BS. More interestingly, regression with time histories of the solar wind parameters and the AE index preceding the wave measurements outside the plasmapause shows significant dependence on the IMF BS, NSW, and AE: the region of peak coefficients is changed with time delay for IMF BS and AE, while isolated peaks around duskside remain gradually decrease with time for NSW. In addition, the regression with magnetosonic waves inside the plasmapause shows high coefficients around prenoon sector with preceding IMF BS and VSW. Kim, Kyung-Chan; Shprits, Yuri; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2017 YEAR: 2017 DOI: 10.1002/2017JA024094 magnetosonic equatorial noise; solar wind dependence; Van Allen Probes |
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Climatology of high-β plasma measurements in Earth\textquoterights inner magnetosphere Since their launch in August 2012, the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instruments on the NASA Van Allen Probes spacecraft have been making continuous high-resolution measurements of Earth\textquoterights ring current plasma environment. After a full traversal through all magnetic local times, a climatology (i.e., a survey of observations) of high-beta (β) plasma events (defined here as β > 1) as measured by the RBSPICE instrument in the \~45 keV to \~600 keV proton energy range in the inner magnetosphere (L < 5.8) has been constructed. In this paper we report this climatology of such high-β plasma occurrences, durations, and their general characteristics. Specifically, we show that most high-β events in the RBSPICE energy range are associated with postdusk/premidnight sector particle injections or plasma patches and can last from minutes to hours. While most of these events have a β less than 2, there are a number of observations reaching β greater than 4. Other observations of particular note are high-β events during relatively minor geomagnetic storms and examples of very long duration high-β plasmas. We show that high-β plasmas are a relatively common occurrence in the inner magnetosphere during both quiet and active times. As such, the waves generated by these plasmas may have an underappreciated role in the inner magnetosphere, and thus the study of these plasmas and their instabilities may be more important than has been currently addressed. Cohen, Ross; Gerrard, Andrew; Lanzerotti, Louis; Soto-Chavez, A.; Kim, Hyomin; Manweiler, Jerry; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022513 climatology; high-beta plasma; inner magnetosphere; RBSPICE; Van Allen Probes |
| 2016 |
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Climatology of high β plasma measurements in Earth\textquoterights inner magnetosphere Since their launch in August 2012, the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instruments on the NASA Van Allen Probes spacecraft have been making continuous high resolution measurements of Earth\textquoterights ring current plasma environment. After a full traversal through all magnetic local times, a climatology (i.e., a survey of observations) of high beta (β) plasma events (defined here as β>1) as measured by the RBSPICE instrument in the \~45-keV to \~600-keV proton energy range in the inner magnetosphere (L<5.8) has been constructed. In this paper we report this climatology of such high β plasma occurrences, durations, and their general characteristics. Specifically, we show that most high β events in the RBSPICE energy range are associated with post-dusk/pre-midnight sector particle injections or plasma patches and can last from minutes to hours. While most of these events have a β less than 2, there are a number of observations reaching β greater than 4. Other observations of particular note are high β events during relatively minor geomagnetic storms and examples of very long duration high β plasmas. We show that high β plasmas are a relatively common occurrence in the inner magnetosphere during both quiet and active times. As such, the waves generated by these plasmas may have an under-appreciated role in the inner magnetosphere, and thus the study of these plasmas and their instabilities may be more important than has been currently addressed. Cohen, Ross; Gerrard, Andrew; Lanzerotti, Louis; Soto-Chavez, A.; Kim, Hyomin; Manweiler, Jerry; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016JA022513 climatology; high beta plasma; inner magnetosphere; RBSPICE; Van Allen Probes |
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A strongly energy-dependent ring current ion loss was measured by the RBSPICE instrument on the Van Allen Probes A spacecraft in the local evening sector during the 17 March 2015 geomagnetic storm. The ion loss is found to be energy dependent where only ions with energies measured above \~ 150 keV have a significant drop in intensity. At these energies the ion dynamics are principally controlled by variations of the geomagnetic field which, during magnetic storms, exhibits large scale variations on timescales from minutes to hours. Here we show that starting from \~ 19:10 UTC on March 17 the geomagnetic field increased from 220 to 260 nT on a time scale of about an hour as captured by RBSPICE-A close to spacecraft apogee, L = 6.1 and MLT = 21.85 hr. [GSM coordinates X=-4.89, Y=3.00, Z=-0.73)]. We demonstrate the relationship between this large geomagnetic field increase and the drop-outs of the inline image 150 keV ring current ions. Soto-Chavez, A.; Lanzerotti, L.; Gerrard, A.; Kim, H.; Bortnik, J.; Manweiler, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022512 inner magnetosphere; Magnetic Storms; Ring current ion.; Van Allen Probes |
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Magnetospheric compression due to impact of enhanced solar wind dynamic pressure Pdyn has long been considered as one of the generation mechanisms of electromagnetic ion cyclotron (EMIC) waves. With the Van Allen Probe-A observations, we identify three EMIC wave events that are triggered by Pdyn enhancements under prolonged northward IMF quiet time preconditions. They are in contrast to one another in a few aspects. Event 1 occurs in the middle of continuously increasing Pdyn while Van Allen Probe-A is located outside the plasmapause at post-midnight and near the equator (magnetic latitude (MLAT) ~ -3o). Event 2 occurs by a sharp Pdyn pulse impact while Van Allen Probe-A is located inside the plasmapause in the dawn sector and rather away from the equator (MLAT ~ 12o). Event 3 is characterized by amplification of a pre-existing EMIC wave by a sharp Pdyn pulse impact while Van Allen Probe-A is located outside the plasmapause at noon and rather away from the equator (MLAT ~ -15o). These three events represent various situations where EMIC waves can be triggered by Pdyn increases. Several common features are also found among the three events. (i) The strongest wave is found just above the He+ gyrofrequency. (ii) The waves are nearly linearly polarized with a rather oblique propagation direction (~28o to ~39o on average). (iii) The proton fluxes increase in immediate response to the Pdyn impact, most significantly in tens of keV energy, corresponding to the proton resonant energy. (iv) The temperature anisotropy with T⊥ > T|| is seen in the resonant energy for all the events, although its increase by the Pdyn impact is not necessarily always significant. The last two points (iii) and (iv) may imply that, in addition to the temperature anisotropy, the increase of the resonant protons must have played a critical role in triggering the EMIC waves by the enhanced Pdyn impact. Cho, J.-H.; Lee, D.-Y.; Noh, S.-J.; Shin, D.-K.; Hwang, J.; Kim, K.-C.; Lee, J.; Choi, C.; Thaller, S.; Skoug, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022841 |
| 2015 |
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Simultaneous Pi2 observations by the Van Allen Probes inside and outside the plasmasphere Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L = ~6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L = ~5). VAP-B observed oscillations in the compressional magnetic field component (Bz) and the dawn-to-dusk electric field component (Ey), having high coherence with the BOH Pi2 pulsation in the H component. The H - Bz and H - Ey cross phases at VAP-B inside the plasmasphere were near -180\textdegree and -90\textdegree, respectively.These phase relationships among Bz, Ey, and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, Bz oscillations were highly correlated with BOH Pi2 pulsations with ~-180\textdegree phase delay, and the H-Ey cross phase is near -90\textdegree. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B. Ghamry, E.; Kim, K.-H.; Kwon, H.-J.; Lee, D.-H.; Park, J.-S.; Choi, J.; Hyun, K.; Kurth, W.; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021095 Pi2; plasmasphere; Plasmaspheric virtual resonance; Van Allen Probes |
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We investigate an electron flux dropout during a weak storm on 7\textendash8 November 2008, with Dst minimum value being -37 nT. During this period, two clear dropouts were observed on GOES 11 > 2 MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time and propagates into the dayside following electron drift direction. That resupply of the particles might be caused by substorm injections due to enhanced convection. We found a significant precipitation in hundreds keV electrons during the dropout. We observe electromagnetic ion cyclotron and chorus waves both on the ground and in space. We find the drift shells are opened near the beginning of the first dropout. The dropout in MeV electrons at GEO might therefore be initiated due to the magnetopause shadowing, and the followed dropout in hundreds keV electrons might be the result of the combination of magnetopause shadowing and precipitation loss into the Earth\textquoterights atmosphere. Hwang, J.; Choi, E.-J.; Park, J.-S.; Fok, M.-C.; Lee, D.-Y.; Kim, K.-C.; Shin, D.-K.; Usanova, M.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021085 atmospheric precipitation; flux dropout; Geomagnetic storm; magneopause shadowing; Radiation belt; RBE model |
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It is well known that the plasmapause is influenced by the solar wind and magnetospheric conditions. Empirical models of its location have been previously developed such as those by O\textquoterightBrien and Moldwin (2003) and Larsen et al. (2006). In this study, we identified the locations of the plasmapause using the plasma density data obtained from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. We used the data for the period (2008\textendash2012) corresponding to the ascending phase of Solar Cycle 24. Our database includes data from over a year of unusually weak solar wind conditions, correspondingly covering the plasmapause locations in a wider L range than those in previous studies. It also contains many coronal hole stream intervals during which the plasmasphere is eroded and recovers over a timescale of several days. The plasmapause was rigorously determined by requiring a density gradient by a factor of 15 within a radial distance of 0.5 L. We first determined the statistical correlation of the plasmapause locations with several solar wind parameters as well as geomagnetic indices. We found that the plasmapause locations are well correlated with the solar wind speed and the interplanetary magnetic field Bz, therefore the y component of the convective electric field, and some energy coupling functions such as the well-known Akasofu\textquoterights epsilon parameter. The plasmapause locations are also highly correlated with the geomagnetic indices, Dst, AE, and Kp, as recognized previously. Finally, we suggest new model fit functions for the plasmapause locations in terms of the solar wind parameters and geomagnetic indices. When applied to a new data interval outside the model training interval, our model fit functions work better than existing ones. The new model fit functions developed here extend the range of conditions from those used in previous works. Cho, Junghee; Lee, Dae-Young; Kim, Jin-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Turner, Drew; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021030 |
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It is well known that the plasmapause is influenced by the solar wind and magnetospheric conditions. Empirical models of its location have been previously developed such as those by O\textquoterightBrien and Moldwin (2003) and Larsen et al. (2006). In this study, we identified the locations of the plasmapause using the plasma density data obtained from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. We used the data for the period (2008\textendash2012) corresponding to the ascending phase of Solar Cycle 24. Our database includes data from over a year of unusually weak solar wind conditions, correspondingly covering the plasmapause locations in a wider L range than those in previous studies. It also contains many coronal hole stream intervals during which the plasmasphere is eroded and recovers over a timescale of several days. The plasmapause was rigorously determined by requiring a density gradient by a factor of 15 within a radial distance of 0.5 L. We first determined the statistical correlation of the plasmapause locations with several solar wind parameters as well as geomagnetic indices. We found that the plasmapause locations are well correlated with the solar wind speed and the interplanetary magnetic field Bz, therefore the y component of the convective electric field, and some energy coupling functions such as the well-known Akasofu\textquoterights epsilon parameter. The plasmapause locations are also highly correlated with the geomagnetic indices, Dst, AE, and Kp, as recognized previously. Finally, we suggest new model fit functions for the plasmapause locations in terms of the solar wind parameters and geomagnetic indices. When applied to a new data interval outside the model training interval, our model fit functions work better than existing ones. The new model fit functions developed here extend the range of conditions from those used in previous works. Cho, Junghee; Lee, Dae-Young; Kim, Jin-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Turner, Drew; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021030 |
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Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) Bz and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF Bz or AE index. Two separate models are developed: one based only on the IMF Bz and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10\textdegree, and |MLAT| = 10\textdegree\textendash25\textdegree. The model performance is measured by the coefficient of determination R2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE-based model works slightly better than the IMF Bz-based model: for the AE-based model, the mean R2 and ROCC values are ~0.46 and ~0.78 for |MLAT| < 10\textdegree, respectively, and ~0.4 and ~0.74 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively; for the IMF Bz-based model, the mean R2 and ROCC values are ~0.39 and ~0.74 for |MLAT| < 10\textdegree, respectively, and ~0.33 and ~0.70 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models. Kim, Jin-Hee; Lee, Dae-Young; Cho, Jung-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Li, Wen; Kim, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020900 |
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Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) Bz and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF Bz or AE index. Two separate models are developed: one based only on the IMF Bz and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10\textdegree, and |MLAT| = 10\textdegree\textendash25\textdegree. The model performance is measured by the coefficient of determination R2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE-based model works slightly better than the IMF Bz-based model: for the AE-based model, the mean R2 and ROCC values are ~0.46 and ~0.78 for |MLAT| < 10\textdegree, respectively, and ~0.4 and ~0.74 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively; for the IMF Bz-based model, the mean R2 and ROCC values are ~0.39 and ~0.74 for |MLAT| < 10\textdegree, respectively, and ~0.33 and ~0.70 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models. Kim, Jin-Hee; Lee, Dae-Young; Cho, Jung-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Li, Wen; Kim, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020900 |
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Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) Bz and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF Bz or AE index. Two separate models are developed: one based only on the IMF Bz and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10\textdegree, and |MLAT| = 10\textdegree\textendash25\textdegree. The model performance is measured by the coefficient of determination R2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE-based model works slightly better than the IMF Bz-based model: for the AE-based model, the mean R2 and ROCC values are ~0.46 and ~0.78 for |MLAT| < 10\textdegree, respectively, and ~0.4 and ~0.74 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively; for the IMF Bz-based model, the mean R2 and ROCC values are ~0.39 and ~0.74 for |MLAT| < 10\textdegree, respectively, and ~0.33 and ~0.70 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models. Kim, Jin-Hee; Lee, Dae-Young; Cho, Jung-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Li, Wen; Kim, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020900 |
| 2014 |
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Magnetopause structure favorable for radiation belt electron loss Magnetopause shadowing is regarded as one of the major reasons for the loss of relativistic radiation belt electrons, although this has not yet been fully validated by observations. Previous simulations on this process assumed that all of the electrons encountering the magnetopause are simply lost into the magnetosheath just as ring current ions can be and did not examine details of the particle dynamics across and inside the magnetopause which has a finite thickness. In this paper, we perform test particle orbit calculations based on a simplified one-dimensional magnetopause model to demonstrate specifically how relativistic electrons arriving at the prenoon side of the magnetopause can be lost. The calculation results indicate that the loss process is determined by two factors: (i) a gradient of the magnetic field magnitude, B, along the magnetopause and (ii) a component of the magnetic field normal to the magnetopause. First, without a normal component of the magnetic field as in a tangential discontinuity, electrons can cross the magnetopause by the magnetic gradient drift motion due to the existence of B-gradient along the magnetopause. The minimum kinetic energies for loss decrease with increasing B-gradient along the magnetopause induced by the enhanced solar wind dynamic pressure. However, this process is not too strong in the sense that electrons have to drift rather a long distance along the magnetopause before entering the magnetosheath unless the B-gradient along the magnetopause is unusually strong, or the particle energy is very high like above 3 MeV. In contrast, if a normal component of the magnetic field exists inside the magnetopause, as in a rotational discontinuity, electrons can cross the magnetopause far more easily along the guided field line inside the magnetopause. This is effective for even a very small magnitude of normal component field such as somewhat less than 1 nT regardless of its direction and for a rather low energy of particles such as 0.5 MeV. Also, the loss occurs over more than half of the pitch angle domain, i.e., in the range between ~80\textdegree and 180\textdegree or 0\textdegree and ~100\textdegree, depending on the direction of normal component. Therefore, we suggest that radiation belt electron loss by the magnetopause shadowing process can be substantial (or can be effective) when a substantial area of the magnetopause is given a finite normal magnetic field component as well as B-gradient along the magnetopause. Kim, Kyung-Chan; Lee, Dae-Young; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2014 YEAR: 2014 DOI: 10.1002/2014JA019880 magnetopause shadowing; relativistic electron loss; test particle orbit calculation |
| 2013 |
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Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine \textquotedbllefthow space weather creates the storm-time ring current around Earth, how that ring current supplies and supports the creation of the radiation belt populations,\textquotedblright and how the ring current is involved in radiation belt losses. RBSPICE is a time-of-flight versus total energy instrument that measures ions over the energy range from \~20 keV to \~1 MeV. RBSPICE will also measure electrons over the energy range \~25 keV to \~1 MeV in order to provide instrument background information in the radiation belts. A description of the instrument and its data products are provided in this chapter. Mitchell, D.; Lanzerotti, L.; Kim, C.; Stokes, M.; Ho, G.; Cooper, S.; UKHORSKIY, A; Manweiler, J.; Jaskulek, S.; Haggerty, D.; Brandt, P.; SITNOV, M; Keika, K.; Hayes, J.; Brown, L.; Gurnee, R.; Hutcheson, J.; Nelson, K.; Paschalidis, N.; Rossano, E.; Kerem, S.; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9965-x |
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Unusual stable trapping of the ultrarelativistic electrons in the Van Allen radiation belts Radiation in space was the first discovery of the space age. Earth\textquoterights radiation belts consist of energetic particles that are trapped by the geomagnetic field and encircle the planet1. The electron radiation belts usually form a two-zone structure with a stable inner zone and a highly variable outer zone, which forms and disappears owing to wave\textendashparticle interactions on the timescale of a day, and is strongly influenced by the very-low-frequency plasma waves. Recent observations revealed a third radiation zone at ultrarelativistic energies2, with the additional medium narrow belt (long-lived ring) persisting for approximately 4 weeks. This new ring resulted from a combination of electron losses to the interplanetary medium and scattering by electromagnetic ion cyclotron waves to the Earth\textquoterights atmosphere. Here we show that ultrarelativistic electrons can stay trapped in the outer zone and remain unaffected by the very-low-frequency plasma waves for a very long time owing to a lack of scattering into the atmosphere. The absence of scattering is explained as a result of ultrarelativistic particles being too energetic to resonantly interact with waves at low latitudes. This study shows that a different set of physical processes determines the evolution of ultrarelativistic electrons. Shprits, Yuri; Subbotin, Dmitriy; Drozdov, Alexander; Usanova, Maria; Kellerman, Adam; Orlova, Ksenia; Baker, Daniel; Turner, Drew; Kim, Kyung-Chan; Published by: Nature Physics Published on: 11/2013 YEAR: 2013 DOI: 10.1038/nphys2760 |
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Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere [1] In this paper, we estimate the size of coherent activity of electromagnetic ion cyclotron (EMIC) waves using the multi-spacecraft observations made during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. We calculate the cross-correlations between EMIC wave powers measured by different THEMIS spacecraft, plot them over the separation distances between pairs of observing spacecraft, and determine the 1/e folding distance of the correlations as the characteristic dimension of the coherent wave activity. The characteristic radius in the direction transverse to the local magnetic field is found to lie in rather a wide range of 1500\textendash8600 km varying from the AM to PM sectors and also from hydrogen to helium bands. However, the characteristic dimensions normalized by either gyroradius or wavelength fall into narrower ranges almost independent of the emission band and event location. Specifically, the coherent dimension is found to be 10\textendash16 times gyroradius of 100 keV protons and 2\textendash3 times local wavelength. The former may give a useful scale for the source dimension, and the latter suggests that the EMIC wave activity maintains coherency only up to a couple of wavelengths. Lee, Jeongwoo; Min, Kyungguk; Kim, Kap-Sung; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2013 YEAR: 2013 DOI: 10.1002/jgra.50242 |
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