Refilling and Composition at Geostationary Orbit

Abstract:

Here we examine the apparent long-term refilling (change in density at a particular position over days) of electron density and mass density. At solar maximum, the changes in these quantities following a period of large geomagnetic activity can be very different. For instance, for events during 2001 we used both the ion density measured by the Los Alamos National Lab (LANL) Magnetospheric Plasma Analyzer (MPA) instrument and mass density inferred from Alfven wave frequencies measured by the Geostationary Operational Environmental Satellites (GOES) to show that the mass density varied comparatively little while the electron density dropped down to a low value and recovered slowly. During this event, the composition changed dramatically, from a high concentration of O+ very soon after large geomagnetic activity to a very low concentration of O+ after a long quiet period. This result suggests that at solar maximum O+ is quickly distributed to the region outside the plasmasphere sometimes called the warm plasma cloak while H+ refills this region much more slowly. Here we use a large database of mass density measurements based on Alfven waves observed by GOES to examine statistically the behavior of the mass density during periods of quiet following large geomagnetic activity and to see how this behavior varies over the solar cycle. We will compare with previous results for refilling of electron density.