Traveling convection vortices induced by solar wind tangential discontinuities
19 December 2002
Two typical magnetic impulse events (MIEs) accompanied by traveling convection vortices (TCVs) are investigated. The analysis of their conjugate equivalent convection patterns is performed using magnetic field data obtained from high-latitude ground magnetometer networks in the northern and southern hemispheres. The 3-D analysis of solar wind structures is also performed using the solar wind data obtained from multiple ISTP satellites. In the first event observed at ~1310 UT on May 22, 1996, a westward moving TCV appeared in the noon-to-dawn sector in the northern and southern hemisphere simultaneously. The solar wind source of this TCV is found to be a tangential discontinuity (TD) exhibiting a rapid northward turning of the interplanetary magnetic field (IMF) and abrupt dynamic pressure changes. In the second event observed at ~1610 UT on May 27, 1998, an eastward moving TCV appeared in the noon sector in the northern and southern hemisphere with a timing delay of 2-3 min in the southern hemisphere. The solar wind source of this TCV is found again to be a TD exhibiting a rapid IMF By negative turning and an abrupt enhancement of dynamic pressure. It is found that the TDs driving these events have the motional electric fields pointing toward the TDs and the normal vectors with large cone angles from the sunward direction. These TDs satisfy the conditions for hot flow anomaly (HFA) formation at the bow shock, and the sweep motion of the intersection of the TD and the bow shock is found to be consistent with the observed TCV motion in each event. Magnetopause deformations due to HFAs can explain all the observed morphological features and the triggering process of these MIEs. It is suggested, however, that bursty merging and/or pressure pulses would reinforce the processes produced by HFAs, since the TDs are usually accompanied by both abrupt IMF changes and pressure enhancements. Consequently it seems reasonable to conclude that the integrated processes of HFA, bursty merging, and pressure pulse produce the evolution of MIEs and TCVs.