Electron density and plasmapause characteristics at 6.6 R_E: A statistical study of the GEOS 2 relaxation sounder data

Abstract

On board the geostationary GEOS 2, a relaxation sounding (RS) experiment using a pulsed active wave technique has been operated in the frequency range 0.3–77 kHz. In situ measurements of the equatorial magnetospheric electron density at L ≃ 6, obtained in the range from 0.1 to ∼100 cm−3 through on line data processing, are presented. The results from 4 months of routine operations (November 20, 1978–March 28, 1979) are statistically studied. Many features of the density distributions at 6.6 RE displayed from GEOS 2 RS data corroborate the morphological characteristics evidenced in past experimental data sets of magnetospheric density, like those from ground‐based whistler observation and from embarked particle experiments. In providing an improved accuracy—especially for the cold plasma density—and unique coverage in space and time, the GEOS 2 RS data set brings some extension of results. The average properties of different magnetospheric regions that can be sampled at 6.6 RE with respect to LT are focused: the dayside plasma trough, with a few cm−3 typically, the plasmaspheric bulge (a few tens of cm−3) and the associated plasmapause crossings (variations in cm−3 per minute), and the geosynchronous nightside where the density fluctuates in the lower range available (0.1–1 cm−3). The important contribution of cold plasma to the dayside magnetospheric density is reported. There are striking variabilities of the density distributions found from day to day, especially as far as the plasmaspheric bulge morphology is concerned. Relationships between geomagnetic activity and both the LT position and the LT width of the bulge are found. They confirm the role played by timing effects on the large scale convection patterns, which experimental and model studies performed earlier on the plasmapause dynamics have focused on.

Medium energy pitch angle distribution during substorm injected electron clouds

“…, well within the observed range of densities at geosynchronous orbit [Higel and Wu, 1984]. Even if the gap between the two whistler mode bands at 0.5W ce has a width up to 0.2W ce [Koons and Roeder, 1990] this estimate of the magnetic energy per particle will only be off by 4%.…”

Refilling process in the plasmasphere: a 3-D statistical characterization based on Cluster density observations

“…A bulge of high densities (n e ∼ 50 cm −3 ) shows up in the dusk sector (15:00-21:00 MLT range). This is the region where, according to a classical interpretation, the co-rotation electric field and the convection electric field are equal and opposite (Carpenter, 1967;Chappell et al, 1970;Higel and Lei, 1984). Note also the local increase of the plasmapause-like boundary at 21:00 MLT (patch in grey colour up to L = 6).…”

The story of plumes: the development of a new conceptual framework for understanding magnetosphere and ionosphere coupling

“…Regions of high-density plasma were also observed beyond the plasmapause in the earliest high-inclination low-Earth orbit (e.g., Taylor et al, 1970Taylor et al, , 1971 and equatorial elliptical and geosynchronous orbit satellite missions (e.g., Chappell, 1974;Higel and Lei, 1984;McComas et al, 1993). These were called plasmaspheric "tails" (Chappell, 1975;Maynard and Chen, 1975) or detached plasma or blobs (e.g., Chappell et al, 1970).…”