Roles of double lobe reconnection and Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet: A statistical study

Details Roles of double lobe reconnection and Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet: A statistical study Roles of double lobe reconnection and Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet: A statistical study

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm52a..03h&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM52A-03

Physics

[2724] Magnetospheric Physics / Magnetopause And Boundary Layers, [2764] Magnetospheric Physics / Plasma Sheet, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions

Scientific paper

It is well known that the plasma sheet becomes cold and dense under prolonged northward IMF conditions [e.g., Terasawa et al., 1997]. Two major candidates, (1) high latitude reconnections in both hemispheres which capture magnetosheath plasmas on the newly closed field lines (double lobe reconnection) [e.g., Song and Russell, 1992] and (2) effective diffusive transport of magnetosheath plasma induced by the Kelvin-Helmholtz instability at the flank magnetopause [e.g., Hasegawa et al., 2004], have been discussed to account for the formation of the cold dense plasma sheet. The relative importance of the double lobe reconnection and the Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet is so far an open question. We quantitatively examined the properties of the cold dense plasma sheet by fitting the observed ion and electron velocity distributions to a single/two-component Maxwellian. We statistically show that the cold dense plasma sheet in the dusk magnetosphere is characterized by ions consisting of separate cold and hot component and electrons consisting of a single cold component. Although the absence of a hot electron component in the cold dense plasma sheet can be explained naturally if we blame the formation of the cold dense plasma sheet on the double lobe reconnection scenario, it is hard to be explained by diffusion induced by the Kelvin-Helmholtz instability at the magnetopause. We also show that a sharp boundary exists between the cold dense plasma sheet and the hot tenuous plasma sheet. The observed velocity distributions of ions and electrons in the cold dense plasma sheet bordered by the hot tenuous plasma sheet indicate the supply of the hot ion component by diffusion and gradient/curvature B drift. The cold dense plasma sheet observed just inside the Kelvin-Helmholtz unstable magnetopause further suggests that the double lobe reconnection and the Kelvin-Helmholtz instability can occur simultaneously.

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