SIMULATIONS of MAGNETOPAUSE FLUCTUATIONS

ABSTRACT:

The magnetopause often exhibits large scale surface wave
activity both in observational data and in global simulation
results.  Many of these waves are observed to be directly
driven by solar wind disturbances.  Here we report on
waves seen in global MHD simulations of the Earth's
magnetosphere which are not directly driven.  These
oscillations first become apparent a few Re away from the
subsolar point and grow as they move tailward at less than
the magnetosheath flow speed.  The waves exhibit vortices
in the plasma flow.  At the terminator the vortices can be
a few Re in diameter.  In the examples shown, the period of
these fluctuations is approximately 5 min.  A possible
explanation for this behavior is the Kelvin-Helmholtz
instability.  We will discuss this and other possible
interpretations.  The simulation results are directly
compared with Geotail observations.