  We have developed a model predicting whether or not the magnetopause crosses
geosynchronous orbit at given location for given solar wind pressure Psw, Bz
component of interplanetary magnetic field (IMF) and geomagnetic conditions
characterized by 1-min SYM-H index. The model is based on more than 300
geosynchronous magnetopause crossings (GMCs) and about 6000 minutes when
geosynchronous satellites of GOES and LANL series are located in the
magnetosheath (so-called MSh intervals) in 1994 to 2001. Minimizing of the Psw
required for GMCs and MSh intervals at various locations, Bz and SYM-H allows
describing both an effect of magnetopause dawn-dusk asymmetry and saturation of
Bz influence for very large southward IMF. The asymmetry is strong for large
negative Bz and almost disappears when Bz is positive. We found that the larger
amplitude of negative SYM-H the lower solar wind pressure is required for GMCs.
We attribute this effect to a depletion of the dayside magnetic field by a
storm-time intensification of the cross-tail current. It is also found that the
magnitude of threshold for Bz saturation increases with SYM-H index such that
for small negative and positive SYM-H the effect of saturation diminishes. This
supports an idea that enhanced thermal pressure of the magnetospheric plasma
and ring current particles during magnetic storms results in the saturation of
magnetic effect of the IMF Bz at the dayside magnetopause. A noticeable
advantage of the model prediction capabilities in comparison with other
magnetopause models makes the model useful for space weather predictions.
Supplement : a program-code of the GMC-model
