A comprehensive survey of plasmasphere refilling at geosynchronous orbit

Abstract

Abstract. Plasmasphere refilling is one of th• most fundamental examples of ionosphere-magnetosphere coupling. Geosynchron0us low-energy ion measurements are particularly useful in addressing this issue. In this survey we collect almost 11 satellite years of data, from January 1990 to September 2000, from Los Alamos magnetospheric plasma analyzers on board five satellites. The data are sorted according to the level of magnetospheric activity, local time, season, and solar cycle phase for a comprehensive examination of the early-time refilling rate. These statistical results indicate that the early-time refilling rate increases with increasing geomagnetic activity. Additionally, the early-time refilling rate at low solar activity is about a factor of 1.5-2 higher than that at high solar activity. This may be related to the higher ionospheric neutral hydrogen density at solar minimum. Moreover, when the geomagnetic activity index is higher than 3, the early-time refilling rate is observed to be slightly higher during the seasonal equinox periods than •t solstice, but no seasonal variation is •found at low geomagnetic activity.

Simulation of field-aligned H<sup>+</sup> and He<sup>+</sup> dynamics during late-stage plasmasphere refilling

“…At the present time, both the data (Park, 1970;Sojka and Wrenn, 1985;Song et al, 1988;Singh and Horwitz, 1992;Lawrence et al, 1999;Su et al, 2001;Tu et al, 2003) and the models show that for a given flux tube, refilling begins with high-speed upflows from the two conjugate ionospheric sources, followed by a process in which the plasma is trapped or thermalized and, lastly, by a fluid-like evolution over a number of days. In general, early stage refilling (inflow and trapping; t<24 h) proceeds at a lower rate than late stage refilling (>24 h) (Lawrence et al, 1999).…”

The local-time variation of the quiet plasmasphere: geosynchronous observations and kinetic theory

“…With late-time refilling, no assumptions about the convection pattern were made, since only the local time was used to determine the rate. Thus, Su et al (2001) came to the same conclusions regarding the two stage nature of the refilling process.…”

“…The exact value of this choice is not critical, as all percentile levels exhibit similar local-time behavior. In fact, Su et al (2001), who chose the 70th percentile, showed that the choice of percentile level affects the numerical value of the density, but does not affect the trend of refilling. That is, they found similar late-time refilling rates regardless of the percentile chosen.…”

“…Both of the above studies, however, assumed that the flux tubes were exactly corotating with the spacecraft. As an improvement, Su et al (2001) reevaluated the early time results of Thomsen et al (1998) and Lawrence et al (1999) by utilizing a realistic convection electric field, which can modify the assumed refilling time by up to 2 h, as well as using a ten-year period (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000). With this more sophisticated model, the early-time refilling rate was slightly modified to 2.5-6.5 cm −3 day −1 .…”

“…There have been several recent studies of plasmaspheric refilling using observations of the LANL satellites at geosynchronous orbit (Thomsen et al, 1998;Lawrence et al, 1999;Su et al, 2001). This series of three papers characterizes the temporal variation of the plasma density at geosynchronous orbit that is indicative of the refilling process.…”