A density‐temperature description of the outer electron radiation belt during geomagnetic storms

Abstract

[1] Bi-Maxwellian fits are made to energetic-electron flux measurements from seven satellites in geosynchronous orbit, yielding a number density (n) and temperature (T) description of the outer electron radiation belt. For 54.5 spacecraft years of measurements the median value of n is 3.7 Â 10 À4 cm À3 , and the median value of T is 148 keV. General statistical properties of n, T, and the 1.1-1.5 MeV flux F are investigated, including localtime and solar-cycle dependencies. Using superposed-epoch analysis where the zero epoch is convection onset, the evolution of the outer electron radiation belt through high-speed-stream-driven storms is investigated. The number-density decay during the calm before the storm, relativistic-electron dropouts and recoveries, and the heating of the outer electron radiation belt during storms are analyzed. Using four different ''triggers'' (sudden storm commencement (SSC), southward interplanetary magnetic field (IMF) portions of coronal mass ejection (CME) sheaths, southward-IMF portions of magnetic clouds, and minimum Dst) a selection of CME-driven storms are analyzed with superposed-epoch techniques. For CME-driven storms, only a very modest density decay prior to storm onset is found. In addition, the compression of the outer electron radiation belt at the time of SSC is analyzed, the number-density increase and temperature decrease during storm main phase are characterized, and the increase in density and temperature during storm recovery phase is determined. During the different phases of storms, changes in the flux are sometimes in response to changes in the temperature, sometimes to changes in the number density, and sometimes to changes in both. Differences are found between the density-temperature and flux descriptions, and it is concluded that more information is available using the density-temperature description.Citation: Denton, M. H., J. E. Borovsky, and T. E. Cayton (2010), A density-temperature description of the outer electron radiation belt during geomagnetic storms,

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

“…where y is a vector of observed counts, δt is the integration time, G is a vector of energy-geometric factors (response functions), j (E) is the omni-directional differential particle Following previous work, and consistent with observation (Cayton et al, 1989;Varotsou et al, 2008;Denton et al, 2010), a relativistic Maxwellian energy spectrum is assumed in the inversion procedure:…”

Density and temperature of energetic electrons in the Earth's magnetotail derived from high-latitude GPS observations during the declining phase of the solar cycle

“…Fast solar wind is known to be strongly correlated with higher fluxes and higher density in the outer electron radiation belt at geosynchronous ter plots of the electron density (N) (top panel), electron temperature (T) (middle panel) and panel) derived from measurements by GPS spacecraft at high-latitude and then mapped to the using the Tsyganenko T89 model as a function of LT and L. Substantial overlap of the 151574 rs in the region closest to Earth. orbit, particularly during HSS-events (Borovsky et al, 1998;Borovsky and Denton, 2009;Denton et al, 2010). Our analysis shows that the density of energetic electrons in the magnetotail follows this trend.…”

“…The mean value of density and temperature are very similar to those found in the outer electron radiation belt (cf. Denton et al, 2010). Since the majority of the GPS data are inferred to map to the region between L = 6 and L = 8, this gives us some measure of confidence that the fitting technique is robust.…”

“…In this study we apply a similar technique to that previously used in analysis of data from geosynchronous orbit. The technique, first implemented by Cayton et al (1989) and subsequently by Borovsky et al (1998), Borovsky and Denton (2009), Denton et al (2010), and Borovsky and Cayton (2011), has proved successful in helping understanding radiation belt dynamics, particularly during high-speed-solarwind-stream (HSS) events. The Combined X-ray and Dosimeter (CXD) (Distel et al, 1999) instruments now operating on 10 Global Positioning System (GPS) satellites, NS53 through NS62, of the GPS replenishment and follow-on series (identified by the designations, Block IIR and IIF) include two subsystems for monitoring energetic electrons: the Low Energy Particle (LEP) subsystem resolves 0.14 to >1.25 MeV electrons into 5 deposited-energy channels; the High-energy X-ray and Particle (HXP) subsystem resolves 1.3 to >5.8 MeV electrons into 6 deposited-energy channels.…”

Subcritical Growth of Electron Phase-space Holes in Planetary Radiation Belts

“…, as the energetic electron density, n h , only accounted for a small portion of the total electron density, n n n 0.1% 1% Spjeldvik 1977b;Denton et al 2010), and precipitated electrons only accounted for a fraction of the hot and cold electron density. Based on observations (Mozer et al 2013;Malaspina et al 2014), large electron holes, q T 1 e c f  , with potential energy of the order of the cold electron temperature, T e c , can form in the radiation belts.…”