1Solar-Terrestrial Environment Laboratory Nagoya University Honohara 3-13, Toyokawa, Aichi 442-8507 Japan, Toyokswa, Japan
2Space Physics Research Laboratory The University of Michigan , Ann
Arbor, MI 48109, United States
3IGPP, UCLA, Los Angeles, CA 90095, United States
4Los Alamos National Laboratoy Los Alamos, NM 87545, United States
As a precursor of the solar maximum of the solar cycle 23, extreme solar wind conditions have occurred frequently. During such an example on May 4, 1998, the WIND spacecraft observed a period of extremely strong southward IMP (-30 nT). The magnetopause moved inside the geosynchronous orbit, exposing LANL geosynchronous, satellites and POLAR to the magnetosheath and even solar wind plasmas. This rare event provides us with an opportunity to study the magnetopause erosion caused by southward IMF. In a simple model, the erosion may be linearly proportional to a southward IMF. A careful analysis of a data set of magnetopause crossings indicates a possible nonlinear dependence of the erosion on IMF Bz. However, because of the scarcity of the data points under this extreme condition in the data set, the statistical significance of the trend is low. We perform a case study using several magnetopause models and in situ observations from LANL satellites and POLAR during the May 4, 1998 event to examine the dependence of the magnetopause erosion on southward IMF.