Abstract. Typical electron velocity distribution functions observed at 1 AU from the Sun by the 3DP instrument onboard Wind are used as boundary conditions to determine the electron velocity distribution function at 4 solar radii in the corona.The velocity distribution functions (VDFs) at low altitude are obtained by solving the Fokker-Planck equation, using two different sets of boundary conditions. The first set typically corresponds to a VDF observed in. a low-speed solar wind flow (i.e., characterized by "core" and "halo" electrons); the second one corresponds to highspeed solar wind (i.e., characterized by "core," "halo,", and "strahl" populations).We use the observed electron VDFs as test particles, which are submitted to external forces and Coulomb collisions with a background plasma. Closer to the Sun, the relative density of the core electrons is found to increase compared to the density of the halo population. Nevertheless, we find that in order to match the observed distributions at i AU, suprathermal tails have to be present in the VDF of the test electron at low altitudes in the corona.
The mechanism of plasmapause formation based on interchange instability and a Kp‐dependent magnetospheric electric field model, enables us to determine the position of the plasmapause as a function of Kp and local time. We illustrate here how this physical mechanism is able to account for the formation of shoulders like those observed by EUV on IMAGE. A wide variety of other structures observed by IMAGE like tails (also called plumes), and notches are also obtained with this mechanism for the formation of a “knee” in the high altitude cross‐L distribution of the cold plasma density distribution.
Abstract. Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles have been derived from the electron plasma frequency identified by the WHISPER sounder supplemented, in-between soundings, by relative variations of the spacecraft potential measured by the electric field instrument EFW; ion velocity is also measured onboard these satellites. The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 R E every 10 min; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations of three plume events and compare CLUSTER in-situ data with global images of the plasmasphere obtained by IMAGE. In particular, we study the geometry and the orientation of plasmaspheric plumes by using four-point analysis methods. We compare several aspects of plume motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary as observed by the wave experiment WHISPER on the four spacecraft, (ii) drift velocity measured by the electron drift instrument EDI onboard CLUSTER and (iii) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate Correspondence to: F. Darrouzet (fabien.darrouzet@oma.be) around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.
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