Magnetopause instabilities during passage of the rear of the January 1997 magnetic cloud

C. J. Farrugia, F. T. Gratton, J. E. Contin, R. B. Torbert, G. Zastenker, M. Nozdrachev, A. Federov, J. M. Quinn, K. W. Ogilvie, H. K. Biernat, N. V. Erkaev, and R. P. Lepping

Institute for the Study of Earth, Oceans, and Space, Space Science Center, University of New Hampshire, Durham, NH USA


Two interplanetary features are likely to influence the magnetosphere most during passage of the trailing edge of the January 1997 magnetic cloud (0030-0500 UT, January 11, 1997): (1) the strongly northward-pointing magnetic fields; and (b) the large and rapid changes in the dynamic pressure. The former provide ideal conditions for exciting the Kelvin-Helmholtz (KH) instability at the dayside magnetopause; the latter set upon undulations on the magnetopause and also influence KH growth rates. We elaborate a simplified theory of KH wave generation, including also the re-inforcement of the KH instability by sunward accelerated motions of the magnetopause. We conclude that intense KH wave generation existed at the magnetopause for about 3 hours. The highly compressed magnetosphere allowed the Interball/tail spacecraft to be near the magnetopause a few RE tailward of the dawn-dusk meridian and near the GSM equator. Comparing theoretical predictions with Interball/tail measurements, we find the presence of KH surface waves lasting for a long time. Other wave types are also observed by Interball/tail. and we propose generating mechanisms for these.

in The Solar Wind - Magnetosphere System 3, edited by J. K. Biernat, C. J. Farrugia, and D. F. Vogl, p. 199, Verlag der Österreichischen Akademie der Wissenschaften, Austria, 2000