Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm11c..06s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM11C-06
Other
2724 Magnetopause, Cusp, And Boundary Layers, 2740 Magnetospheric Configuration And Dynamics, 2752 Mhd Waves And Instabilities, 2764 Plasma Sheet, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
It is observationally known that the plasma sheet becomes much cooler and denser than usual under prolonged northward interplanetary magnetic field (IMF) conditions [e.g., Terasawa et al., 1997]. However, the mechanism responsible for the formation of CDPS is still far from understood. The Kelvin-Helmholtz (K-H) instability driven by the velocity shear at the magnetopause has been proposed as a possible mechanism of magnetosheath plasma entry through the LLBL [Fujimoto and Terasawa, 1994; Otto and Fairfield, 2000; Hasegawa et al., 2004]. Double lobe reconnection, i.e., reconnection of a magnetosheath flux tube with lobe field at the high-latitude magnetopause in both hemispheres, thereby becoming closed, is also an important candidate process for the dense, thick LLBL formation during northward IMF periods [e.g., Song and Russell, 1992]. On the basis of evolution of electron and ion phase space densities (PSDs) from the dayside to the nightside magnetosphere observed by Cluster II, GEOTAIL, and LANL-MPA spacecraft during a northward IMF interval on March 16, 2002, we examine the relative importance of the K-H instability and double lobe reconnection for formation of the CDPS. This event corresponds to one of the CDPS events at geosynchronous orbit during prolonged northward IMF periods [Thomsen et al., 2003]. The heated electron signature observed by Cluster II indicates that formation of closed flux tube(s) through lobe reconnection in both northern and southern hemispheres indeed took place during the event. Comparison of PSDs between the newly closed flux tube observed by Cluster II and the dusk-flank LLBL by GEOTAIL indicates that double lobe reconnection is responsible for formation of the outer-LLBL. On the other hand, GEOTAIL observed wavy structures in the dusk LLBL, and comparison with results from numerical simulation of the K-H instability [Matsumoto et al., 2004] suggests that the observed structure is consistent with the non-linear phase of K-H vortices. The evolution of PSDs in the LLBL suggests that the wavy structure is responsible for the selective plasma entry into the inner LLBL region. The newly-entered plasma from the magnetosheath coexists with hot plasma sheet ions in the LLBL region. Comparison between high-energy populations at GEOTAIL and LANL-MPA locations indicates that the effect of the magnetic drift is prominent for the high-energy population. Taking account of these results, the formation mechanisms of the CDPS under northward IMF condition will be discussed.
Elphic Richard C.
Fazakerley Andrew N.
Lavraud Benoit
Matsumoto Yosuke
Mukai Tadashi
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