A density-temperature description of the outer electronradiation belt during geomagnetic storms

摘要

[1] Bi-Maxwellian fits are made to energetic-electron flux measurements from sevensatellites in geosynchronous orbit, yielding a number density (n) and temperature (T)description of the outer electron radiation belt. For 54.5 spacecraft years of measurementsthe median value of n is 3.7 x 10~(-4)cm~(-3), and the median value of T is 148 keV. Generalstatistical properties of n, T, and the 1.1-1.5 MeV flux F are investigated, including local-time and solar-cycle dependencies. Using superposed-epoch analysis where the zeroepoch is convection onset, the evolution of the outer electron radiation belt throughhigh-speed-stream-driven storms is investigated. The number-density decay during thecalm before the storm, relativistic-electron dropouts and recoveries, and the heating of theouter 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 magneticclouds, and minimum Dst) a selection of CME-driven storms are analyzed withsuperposed-epoch techniques. For CME-driven storms, only a very modest density decayprior to storm onset is found. In addition, the compression of the outer electron radiationbelt at the time of SSC is analyzed, the number-density increase and temperature decreaseduring storm main phase are characterized, and the increase in density and temperatureduring storm recovery phase is determined. During the different phases of storms, changesin the flux are sometimes in response to changes in the temperature, sometimes tochanges in the number density, and sometimes to changes in both. Differences are foundbetween the density-temperature and flux descriptions, and it is concluded that moreinformation is available using the density-temperature description.