MHD flow visualization of magnetopause boundary region vortices observed during high-speed streams

Abstract

We present statistics for a total of 304 vortices found near the ecliptic plane on the magnetopause flanks, using simulated magnetohydrodynamics (MHD) data driven by real solar wind conditions. The study concentrates on 9 hours, from 29 March, 2000 UT to 30 March, 0500 UT, during the onset of a high-speed stream that existed from 29 March to 5 April 2002. Magnetopause crossings seen by the Geotail spacecraft for the 9-hour time interval were also analyzed and compared with the MHD simulation to validate our results. Vortices were classified by solar wind input provided by the Wind satellite located 60-80 RE upstream from Earth. Two hundred seventy-three of the vortices were generated under northward Interplanetary Magnetic Field (IMF), and 31 were generated under southward IMF. The vortices generated under northward IMF were more prevalent on the dawnside than on the duskside and were substantially less ordered on the dawnside than on the duskside. Most of the vortices were large in scale, up to 10 RE, and with a rotation axis closely aligned with the Z SM direction. They rotated preferentially clockwise on the dawnside, and counterclockwise on the duskside. Those generated under southward IMF were less ordered, fewer in number, and also smaller in diameter. Significant vortex activity occurred on the nightside region of the magnetosphere for these southward cases in contrast to the northward IMF cases on which most of the activity was on the magnetopause flanks. The IMF is primarily northward for our time interval, and the development of these vortices with their rotation preference depending on their local time position suggest that a Kelvin-Helmholtz (KH) instability is likely present.