Analysis of Plasmaspheric Plumes: CLUSTER and IMAGE Observations and Numerical Simulations F. Darrouzet, J. De Keyser, P.M. Decreau, V. Pierrard, D.L. Gallagher, B.R. Sandel, J.F. Lemaire, J. Cabrera, I. Dandouras, A. Masson, P. Canu, J. Trotignon, J. Rauch, and M. Andre Plasmaspheric plumes have been routinely observed by two recent magnetospheric missions: CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere crossed at perigee. The total electron density profiles are derived from the plasma frequency (determined from the resonance sounder and wave analyzer WHISPER) and from the spacecraft potential (measured by the electric field instrument EFW). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 Re every 10 minutes. EUV images acquired at apogee show a lot of plasmaspheric plumes, and sequences of such 2-D images show the evolution and motion of these structures. The formation of these plumes has been predicted on the basis of a theoretical model based on the interchange instability mechanism. We present several plume events, e.g., during the April-June 2001 and April 2002 time periods. We compare CLUSTER in-situ observations with global images of the plasmasphere obtained from IMAGE, and with numerical simulations. In particular, we track the plasmaspheric plumes and compare their moving path determined by different methods: (i) bulk velocity measured by the ion spectrometer CIS, (ii) plume boundary velocity calculated from time delays of this boundary observed by WHISPER on the four spacecraft, (iii) drift velocity derived from the electron drift instrument EDI and (iv) global velocity determined from successive EUV images. _______________ Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004