Dropouts of the outer electron radiation belt in response to solar wind stream interfaces: global positioning system observations

Morley, S.; Friedel, R. H. W.; Spanswick, E.; Reeves, G. D.; Steinberg, J. T.; Koller, J.; Cayton, T. E.; Noveroske, E.

doi:10.1098/rspa.2010.0078

Cited by 96 publications

(169 citation statements)

References 55 publications

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“…Such a boundary can account for the magnetopause shadowing as well as the drift splitting, and the amount of electron loss into the solar wind can be explicitly quantified. This paper primarily focuses on quantifying the relative contribution of magnetopause shadowing in the electron flux dropouts during 67 HSS events (from Morley et al, 2010a) by simulating the magnetopause shadowing effect in the 1-D radial diffusion model. Section 2 describes the GPS data that will be used to obtain the total electron loss during HSS dropout events.…”

Section: Y Yu Et Al: Quantifying the Effect Of Magnetopause Shadowingmentioning

confidence: 99%

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Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

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Abstract. Energetic radiation belt electron fluxes can undergo sudden dropouts in response to different solar wind drivers. Many physical processes contribute to the electron flux dropout, but their respective roles in the net electron depletion remain a fundamental puzzle. Some previous studies have qualitatively examined the importance of magnetopause shadowing in the sudden dropouts either from observations or from simulations. While it is difficult to directly measure the electron flux loss into the solar wind, radial diffusion codes with a fixed boundary location (commonly utilized in the literature) are not able to explicitly account for magnetopause shadowing. The exact percentage of its contribution has therefore not yet been resolved. To overcome these limitations and to determine the exact contribution in percentage, we carry out radial diffusion simulations with the magnetopause shadowing effect explicitly accounted for during a superposed solar wind stream interface passage, and quantify the relative contribution of the magnetopause shadowing coupled with outward radial diffusion by comparing with GPS-observed total flux dropout. Results indicate that during high-speed solar wind stream events, which are typically preceded by enhanced dynamic pressure and hence a compressed magnetosphere, magnetopause shadowing coupled with the outward radial diffusion can explain about 60-99 % of the main-phase radiation belt electron depletion near the geosynchronous orbit. While the outer region (L * > 5) can nearly be explained by the above coupled mechanism, additional loss mechanisms are needed to fully explain the energetic electron loss for the inner region (L * ≤ 5). While this conclusion confirms earlier studies, our quantification study demonstrates its relative importance with respect to other mechanisms at different locations.

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Section: Y Yu Et Al: Quantifying the Effect Of Magnetopause Shadowingmentioning

confidence: 99%

“…In this study, we use the superposed epoch results of interplanetary and geomagnetic parameters from 67 HSS events spanning from year 2005 to 2008 studied by Morley et al (2010a) (Fig. 1).…”

Section: Datamentioning

confidence: 99%

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

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“…Based on some of the earliest observations of outer belt electrons, Dessler and Karplus [1961] presented a theory that explained dropouts as simply an adiabatic effect during the main phase of geomagnetic storms: essentially, as the magnetic field strength in the inner magnetosphere dropped during storm main phase, electron drift shells expanded in physical space to conserve the third adiabatic invariant, Φ or L* [Roederer, 1970], and as the particles moved away from the Earth to regions of lower field strength, they lost energy due to conservation of the first and second adiabatic invariants, μ and K. Since there are exponentially fewer particles at higher energy, this adiabatic motion would be observed as a distinct drop in particle flux. However, it has now been shown that dropouts can also occur independent of geomagnetic storms [e.g., Morley et al, 2010] and that the adiabatic effects alone cannot explain the magnitude of loss observed during dropouts [e.g., Kim and Chan, 1997;Li et al, 1997]. The clearest evidence that outer belt dropouts are driven by true losses from the system (i.e., not just adiabatic effects) have resulted from studies of events, revealing that distributions of electron phase space density (PSD) in adiabatic invariant coordinates, which remove most of the ambiguity due to purely adiabatic effects, also undergo outer belt dropouts [e.g., Turner et al, 2013].…”

Section: Introductionmentioning

confidence: 99%

On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event

et al. 2014

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On 30 September 2012, a flux "dropout" occurred throughout Earth's outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA's Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent of the dropout. THEMIS and the Van Allen Probes observed telltale signatures of loss due to magnetopause shadowing and subsequent outward radial transport, including similar loss of energetic ring current ions. However, Van Allen Probes observations suggest that another loss process played a role for multi-MeV electrons at lower L shells (L* <~4).

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“…Morley et al [2010] have conducted a superposed epoch analysis to the electron count dropouts associated with 67 CIRs from 2005 to 2008. They found that the dropouts are related to the increased dynamic pressure during these 67 events associated with solar wind stream interfaces.…”

Section: 1002/2015ja021003mentioning

confidence: 99%

Relativistic electron flux dropouts in the outer radiation belt associated with corotating interaction regions

et al. 2015

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Understanding how the relativistic electron fluxes drop out in the outer radiation belt under different conditions is of great importance. To investigate which mechanisms may affect the dropouts under different solar wind conditions, 1.5–6.0 MeV electron flux dropout events associated with 223 corotating interaction regions (CIRs) from 1994 to 2003 are studied using the observations of Solar, Anomalous, Magnetospheric Particle Explorer satellite. According to the superposed epoch analysis, it is found that high solar wind dynamic pressure with the peak median value of about 7 nPa is corresponding to the dropout of the median of the radiation belt content (RBC) index to 20% of the level before stream interface arrival, whereas low dynamic pressure with the peak median value of about 3 nPa is related to the dropout of the median of RBC index to 40% of the level before stream interface arrival. Furthermore, the influences of Russell‐McPherron effect with respect to interplanetary magnetic field orientation on dropouts are considered. It is pointed out that under positive Russell‐McPherron effect (+RM effect) condition, the median of RBC index can drop to 23% of the level before stream interface arrival, while for negative Russell‐McPherron effect (−RM effect) events, the median of RBC index only drops to 37% of the level before stream interface arrival. From the evolution of phase space density profiles, the effect of +RM on dropouts can be through nonadiabatic loss.

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Dropouts of the outer electron radiation belt in response to solar wind stream interfaces: global positioning system observations

Cited by 96 publications

References 55 publications

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event

Relativistic electron flux dropouts in the outer radiation belt associated with corotating interaction regions

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