Solar wind control of plasma number density in the near-Earth plasma sheet: Correlation analysis of WIND-ACE/GEOTAIL observations

Details Solar wind control of plasma number density in the near-Earth plasma sheet: Correlation analysis of WIND-ACE/GEOTAIL observations Solar wind control of plasma number density in the near-Earth plasma sheet: Correlation analysis of WIND-ACE/GEOTAIL observations

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm31a0305n&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SM31A-0305

Other

2744 Magnetotail, 2748 Magnetotail Boundary Layers, 2760 Plasma Convection (2463), 2764 Plasma Sheet, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Terrestrial plasma sheet is a storage of plasma which feeds ring current, hence storage property of plasma sheet is important for space weather modeling. Plasma sheet number density Nps is controlled by solar wind. The dependence is known as Nps=N0exp(α bz)Nsw^{γ }, where bz is IMFBz and Nsw is solar wind number density. There is also a time lag between IMFBz and Nps. In this paper we investigated XY distribution of α , γ , and time lag based on WIND, ACE, and GEOTAIL observations. α and γ are small in the near-Earth region and large in the midtail flank region. α and γ have weak dawn-dusk asymmetry. On the other hand, time lag has strong dawn-dusk asymmetry. A peak of time lag occurs in the dusk flank region (X=-15Re) and its value is 9 hour. To understand dawn-dusk asymmetry of the time lag, we estimated diffusion time scale and advection time scale based on diffusion-advection equation and plasma flow observations made by GEOTAIL. Diffusion coefficient was calculated under Markov assumption. We found diffusion time scale is 15 hour and advection time scale is 2 hour around the peak of time lag. Both time scales have weak dawn-dusk asymmetry, hence they alone cannot explain the asymmetry of time lag. On the other hand, global convection pattern has dawn-dusk asymmetry. Particularly plasma flow velocity Vx reverses its direction and flow speed is decreased in the dusk flank region. We suggest that the peak of time lag is due to turbulent diffusion around the flow reversal region.

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