MHD experiments to isolate different influences on seasonal variation in MI coupling

It has been known for quite some time that there exists significant seasonal variation in activity within the coupled magnetosphere - ionosphere system. Crooker and Siscoe have proposed a mechacism whcih it explains the variation due to the role of the Earth's dipole tilt in regulating the effecency of energy transfer at the magnetopause. Recently, Newell et al. have proposed an alternative explanation which places the emphasis on the ionospheric conductivity in regulating the rate at which energy from the magnetosphere can be dissipated in the ionosphere. The Lyon-Fedder-Mobarry global MHD magnetosphere model can include and separate both of these effects in control experiments so it provides a useful tool for studying these issues. Some care must be taken in the transformation of Parker spiral magnetic field into GSM coordinates within the simulation domain so we have chosen to conduct simulations with the dipole tilt held fixed at three key times, winter solstice, spring equinox, and summer solstice. In the first set of experiments the full MI electrodynamic coupling interface is enabled which allows for the ionospheric conductivity to be modified to include both the solar EUV effects as well as the enhancements due to auroral precipitation. A second set of runs was conducted with the only the EUV conductivity model enabled thus allowing for a removal of auroral precipitation enchancement effects in the study of the response of the system. We will compare and contrast the polar cap potential, field algined currents, horiztonal currents, and joule heating to quantify the relaltive role of each effect on the coupled MI system.