Annales Geophysicae www.ann-geophys.net 0992-7689 1432-0576 25 9 2007 10.5194/angeo-25-2069-2007 http://www.ann-geophys.net/25/2069/2007/ http://www.ann-geophys.net/25/2069/2007/angeo-25-2069-2007.html http://www.ann-geophys.net/25/2069/2007/angeo-25-2069-2007.pdf 2069 2086 2007-10-02 Origin of temperature anisotropies in the cold plasma sheet: Geotail observations around the Kelvin-Helmholtz vortices M. N. Nishino nishino@stp.isas.jaxa.jp M. Fujimoto G. Ueno T. Mukai Y. Saito School of Science, The University of Tokyo, Tokyo 113-0033, Japan ISAS/JAXA, Kanagawa 229-8510, Japan Institute of Statistical Mathematics, Tokyo 106-8569, Japan JAXA, Tokyo 100-8260, Japan To further our understanding of the solar wind entry across the magnetopause under northward IMF, we perform a case study of a duskside Kelvin-Helmholtz (KH) vortex event on 24 March 1995. We have found that the protons consist of two separate (cold and hot) components in the magnetosphere-like region inside the KH vortical structure. The cold proton component occasionally consisted of counter-streaming beams near the current layer in the KH vortical structure. Low-energy bidirectional electron beams or flat-topped electron distribution functions in the direction along the local magnetic field were apparent on the magnetosphere side of the current layer. We discuss that the bidirectionality of the electrons and the cold proton component implies magnetic reconnection inside the KH vortical structure. In addition, we suggest selective heating of electrons inside the vortical structure via wave-particle interactions. 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