Abstract. Lower hybrid wave cavities detected by the Freja satellite are analyzed. On the basis of simple statistical arguments by use of signals from two density probes, it is possible to obtain rather general results concerning the individual shapes of these cavities. In particular, it is demonstrated that a cylindrically symmetric Gaussian density depletion seems to give a very good fit for a vast majority of cases. The validity of this model is shown to give a great simplification in the interpretation of the data. As a result, a number of well-defined characteristics are obtained which have to be accommodated within an ultimate theory describing the observed wave phenomena.

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Abstract. Data from the Astrid-2 satellite taken between April and July 1999 show several examples of dense ion clouds in the 0.1-2 keV energy range inside the inner magnetosphere, both in the northern and southern hemispheres. These inner magnetospheric ion clouds are found predominantly in the early morning sector, suggesting that they could have originated from substorm-related ion injections on the night side. However, their location and density show no correlation with Kp, and their energy-latitude dispersion is not easily reproduced by a simple particle drift model. Therefore, these ion clouds are not necessarily caused by substormrelated ion injections. Alternative explanations for the ion clouds are the direct solar wind injections and up-welling ions from the other hemisphere. These explanations do not, however, account for all of the observations.