Surface Waves at the Magnetopause: The Kelvin-Helmholtz Source

FARRUGIA, C. J.; GRATTON, F. T.; TORBERT, R.

Huntsville

Workshop; The 2008 Huntsville Workshop; 2008

COSPAR

Abstract. Oscillations of the magnetopause, particularly its flanks, may have several causes, chief among which are rapid changes in the solar wind dynamic pressure, solar wind flow discontinuities, and Kelvin-Helmholtz (KH) instability when the IMF has a strong northward component. We focus here on recent work in the last two sources. Data from various   spacecraft are shown and analyzed by applying compressible, linearized MHD theory for both a 1-scale and 2-scale magnetopause transition. Topics covered are  (i) the existence of special strips of KH activity on the subsonic frontside, which descend to lower latitudes and continue toward the supersonic flanks; (ii) the regulation of KH activity by the IMF orientation, resulting in a dawn--dusk asymmetry of KH activity and a shift to lower frequency waves with decreasing IMF clock angle; (iii) KH surface waves at the flankside magnetopause monitored from the magnetoseath during passage of a magnetic cloud; (iv) the billowy structure of the low latitude boundary layer resulting from KH activity;(v) ambiguities which may arise in applying the KH instability condition valid at tangential discontinuity to a realistic magnetopause structure; (vi) the KH-instabity at a magnetopause layer characterized by two scale lengths; and (vii) features of magnetopause/magnetosphere response to a joint tangential discontinuity/vortex sheet followed by an interval of northward IMF. This work is support by NASA grant NNX08AD11G, NASA Cluster grant to UNH and by Argentine CONICET, grant PIP 5291/05.