Paper#: 16
Poster #:
Session Name: Workshop 4A: Tail Instabilities
Room: 200ABC
Day: Tuesday
Time: 2:40-3:00 p.m.
Abstract Title: Non-Linear Consequences of the Lower Hybrid Drift Instability
PresentSurname: Lapenta, G.
All Authors: G. Lapenta, J.U. Brackbill
Abstract : The LHDI has often been studied for its relevance to the Earth's magnetosphere. It has been proposed as a microinstability able to increase the turbulence of a plasma and in turn cause anomalous resistivity. Unfortunately, the saturation level is insufficient to be of practical importance [1]. Yet, recent new theoretical developments suggest that the LHDI can still be very important but for different reasons. Based on a simulation study we have reached the conclusion that the LHDI affects the evolution of thin current sheets in two ways. First, based on a suggestion by Kuznetsova et al. [2], we find that the LHDI affects the global evolution of the Earth's magnetotail by creating velocity shears [3] that induce a Kelvin-Helmholtz instability (KHI). In thin current sheets, as expected in pre-onset magnetotail configurations, the stability is completely modified with important possible consequences to substorm onset. Second, the process of current sheet thinning is altered profoundly by the LHDI. We find that once the current sheet becomes thin enough (in consequence of flux transfer from the dayside of the magnetosphere) the LHDI causes an additional thinning of the current sheet not previously predicted either by MHD or hybrid simulations. This additional thinning is mostly an electron effect causing the final current sheet to have a two layer structure with a thinner electron current embedded in the wider ion current. [1] J.U. Brackbill, et. al., {\it Phys. Fluids, 27}, 2682 (1984). [2] M.M. Kuznetsova, et. al., {\it EOS, 78}, 625 (1997). [3] G. Lapenta, J.U.. Brackbill, {\it Phys. Plasmas}, submitted (2001).