Dynamic Inner Magnetosphere: A Tutorial and Recent Advances

Ebihara, Yusuke; Miyoshi, Y.

doi:10.1007/978-94-007-0501-2_9

Cited by 33 publications

(29 citation statements)

References 530 publications

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“…A number of studies have examined how the acceleration of radiation belt particles may be related to upstream solar wind conditions, thus giving a way in which to predict future variations in the radiation belt [e.g., Baker et al, 1979;Reeves et al, 2011;McPherron et al, 2009;Li et al, 2015;Kim et al, 2015]. The solar wind can directly influence the radiation belts through the generation of ULF waves and modifying the particle population to generate VLF waves [e.g., Elkington, 2006;Shprits et al, 2008;Ebihara and Miyoshi, 2011;Miyoshi et al, 2013] or can indirectly influence the radiation belts by enhancing the energy of the plasma sheet population prior to substorms that are then subsequently injected [Forsyth et al, 2014;Sergeev et al, 2015]. In this study, we have not considered the impact of the solar wind on the radiation belts but rather statistically examined whether substorm activity alone shows any correspondence to changes in the radiation belt.…”

Section: Discussionmentioning

confidence: 99%

What effect do substorms have on the content of the radiation belts?

et al. 2016

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Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave‐particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM‐H , but decreases in the radiation belt show no apparent link with magnetospheric activity levels.

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Section: Discussionmentioning

confidence: 99%

What effect do substorms have on the content of the radiation belts?

et al. 2016

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“…[3] EMIC waves can interact with radiation belt electrons via Doppler-shifted cyclotron resonance and cause the pitch angle scattering of the electrons and their loss into the atmosphere [e.g., Thorne and Kennel, 1971;Lyons and Thorne, 1972;Horne and Thorne, 1998;Summers et al, 1998;Friedel et al, 2002;Albert, 2003;Meredith et al, 2003;Summers and Thorne, 2003;Shprits et al, 2006;Thorne et al, 2006;Summers et al, 2007aSummers et al, , 2007bJordanova et al, 2008;Miyoshi et al, 2008;Shprits et al, 2008;Albert and Bortnik, 2009;Shprits et al, 2009]. The cyclotron resonance scattering is currently considered one of the leading loss mechanisms of radiation belt electrons [e.g., Onsager et al, 2002;Green et al, 2004;Bortnik et al, 2006;Onsager et al, 2007;Borovsky and Denton, 2009;Ebihara and Miyoshi, 2011;Turner et al, 2012], although its specific contribution to the radiation belt dynamics is not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Global characteristics of electromagnetic ion cyclotron waves: Occurrence rate and its storm dependence

et al. 2013

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[1] We statistically examine the occurrence rate of electromagnetic ion cyclotron (EMIC) waves observed by Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE). We use the 8 Hz magnetic field data set that covers the whole CCE mission period of nearly 4.5 years from August 1984 to January 1989, which is more than three times the period studied by Anderson et al. [1992] (~452 days). The large data volume allows us to evaluate the storm phase dependence of the spatial occurrence pattern of EMIC waves. The major results of this study are summarized as follows. (a) The occurrence rate is below 5% on the nightside at all L. On the dayside, the rate is <5% in the inner magnetosphere (L < 6), while it is higher than 5% in the outer magnetosphere (L ≥ 6), up to 25%. The highest rate appears in the afternoon sector. (b) The overall occurrence rate is higher for H-band events than He-band events, except for the opposite feature seen in the inner magnetosphere on the early afternoon-to-post midnightside (L < 6, 14 h < MLT < 22 h). (c) H-band events occur frequently in the outer magnetosphere (L ≥ 7) in the afternoon sector, regardless of geomagnetic activity. Under quiet conditions, H-band events also occur in the outer magnetosphere on the morningside (4 h ≤ MLT < 8 h). (d) He-band events frequently occur in the inner magnetosphere (L < 7) on the prenoon to duskside (10 h ≤ MLT < 19 h) under disturbed conditions (Dst ≤ À50 nT). (e) The storm time He-band waves are generated more frequently during the main phase than the recovery phase, with the main-phase wave excitation seen toward the afternoonside outer magnetosphere (L > 7). The results indicate two independent major processes that cause EMIC wave excitation in the Earth's magnetosphere: one externally triggers H-band waves on the dayside, and the other internally excites He-band waves on the dusk-to-afternoonside. We suggest that the former is due to solar wind compression which leads to perpendicular adiabatic ion heating and in turn an increase in temperature anisotropy, and that the latter is caused by injections of new, highly energetic ion population from the plasma sheet, with its velocity distributions becoming pancake-like on the dusk-to-afternoonside. The frequent occurrence seen on the afternoonside, at a wide L range, and during the main/development phase, strongly suggests the significant role of the sunward surge of the plasmasphere and plasma plumes in the injection-associated (i.e., storm time) EMIC wave generation.Citation: Keika, K., K. Takahashi, A. Y. Ukhorskiy, and Y. Miyoshi (2013), Global characteristics of electromagnetic ion cyclotron waves: Occurrence rate and its storm dependence,

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“…Two acceleration mechanisms have been proposed: radial diffusion by the geomagnetic pulsations in the ultralow frequency (ULF) range with periods of a few minutes, and cyclotron resonance with whistler mode waves in very low frequency (VLF) range (see reviews by Shprits et al [2008] and Ebihara and Miyoshi [2011]). …”

Section: Introductionmentioning

confidence: 99%

High‐speed solar wind with southward interplanetary magnetic field causes relativistic electron flux enhancement of the outer radiation belt via enhanced condition of whistler waves

Miyoshi

Kataoka

Kasahara

et al. 2013

Geophysical Research Letters

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136

163

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Relativistic electron flux in the outer radiation belt tends to increase during the high‐speed solar wind stream (HSS) events. However, HSS events do not always cause large flux enhancement. To determine the HSS events that cause such enhancement and the mechanisms that are responsible for accelerating the electrons, we analyzed long‐term plasma data sets, for periods longer than one solar cycle. We demonstrate that during HSS events with the southward interplanetary magnetic field (IMF)‐dominant HSS (SBz‐HSS), relativistic electrons are accelerated by whistler mode waves; however, during HSS events with the northward IMF‐dominant HSS, this acceleration mechanism is not effective. The differences in the responses of the outer radiation belt flux variations are caused by the differences in the whistler mode wave–electron interactions associated with a series of substorms. During SBz‐HSS events, hot electron injections occur and the thermal plasma density decreases due to the shrinkage of the plasmapause, causing large flux enhancement of relativistic electrons through whistler mode wave excitation. These results explain why large flux enhancement of relativistic electrons tends to occur during SBz‐HSS events.

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Dynamic Inner Magnetosphere: A Tutorial and Recent Advances

Cited by 33 publications

References 530 publications

What effect do substorms have on the content of the radiation belts?

What effect do substorms have on the content of the radiation belts?

Global characteristics of electromagnetic ion cyclotron waves: Occurrence rate and its storm dependence

High‐speed solar wind with southward interplanetary magnetic field causes relativistic electron flux enhancement of the outer radiation belt via enhanced condition of whistler waves

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