Plasmaspheric electron content

Abstract

Despite substantial work on the problem of the plasmaspheric electron content and of relevant fluxes of cold plasma, there are only few direct experimental determinations, which do not replace but supplement each other.
1. Ionospheric sounding (ground-based and satellite-bornie ionosondes, radar measurements like coherent and incoherent scatter)
2. Whistler measurements
3. Satellite - and rocket - borne instruments (in situ measurements)
4. Satellite Radio Beacon Experiments (RBE) 
Here special emphasis is given to the latter. Application aspects are disregarded here. It is shown, that the total electron content N_T as derived from differential group delay measurements gives a good measure of the slant electron content (up to the altitude of the satellite) for all latitudes, in all cases, when no too strong scintillation occur. Especially in high-latitude regions N_T becomes more and more important, especially as supplementary information for incoherent scatter and so called "heating" experiments. It could be further shown that in midlatitudes the new quantity N_P= N_T-N_F is a good measure of the (residual) electron content between about 2 000 Km and 36 000 Km altitude. Due to this definition and to earlier definitions of the plasmasphere the question arises whether we should further use the terms plasmaspheric, protonospheric or exospheric electron content for N_P or whether we should change it into Residual Electron Content (REC). It is very likely that N_P is the only remote sensing measurement that allows a continuous monitoring of electron fluxes between L = 1 and L = 2. Some of the most important findings deduced from this new quantity N_P are presented. They show, that N_P is a very useful geophysical quantity, that could be relatively easy and inexpensive continuously monitored from many ground stations, provided satellites with Radio Beacon Experiments are available. We are close to the end of the experimental phase of the radio beacon experiments. Fairly soon decisions have to be made by the "application side" as well as by scientist in basic research whether and which, operational radio beacon experiments should be planned.