An overview of magnetopause oscillations driven by velocity gradient flows

GRATTON, F. T.; GNAVI, G.; FARRUGIA, C. J.; BILBAO, L.

Maresias, San Pablo, Brasil

Congreso; X Brazilian Meeting on Plasma Physics; 2009

Sociedade Brasileria de Fisica

Surface oscillations of the magnetopause (MP) have several causes, chief among which are rapid changes in the solar wind dynamic pressure, solar wind flow discontinuities, and Kelvin-Helmholtz (KH) instabilities when the interplanetary magnetic field (IMF) has a strong northward component. We review our recent work on the last two sources. Data from various spacecraft are discussed and interpreted on the basis of linear and non-linear MHD theory, and simulations that model the MP transition. Topics considered are (i) existence of special strips of KH activity on the subsonic frontside; (ii) regulation of KH activity by the IMF orientation, resulting in a shift to lower frequency waves with decreasing clock-angle; (iii) influence of resistivity on the instability: competition between tearing and KH modes; (iv) characteristic features of the KH activity at the pristine magnetopause; (vi) problems that may arise applying the KH stability criterion valid at tangential discontinuity to realistic magnetopause configurations; (vii) features of the magnetopause/magnetosphere response caused by a joint current layer and vortex sheet followed by an interval of northward IMF; (viii) development of secondary non-linear KH instability and formation of counter-rotating vortices. Acknowledgements: FTG, LB and GG are supported by CONICET grant PIP 5291, and UBACYT grant X90. CJF is supported by NASA grants NNX08AD11G, NNG05GG25G, and Cluster grant to UNH.