GLOBAL IONOSPHERE POLAR WIND SYSTEM DURING CHANGING MAGNETIC ACTIVITY

A time-dependent, three-dimensional, multi-ion model of the global ion osphere-polar wind system was used to study the system's response to a n idealized geomagnetic storm for different seasonal and solar cycle c onditions. The model covered the altitude range from 90 to 9000 km for latitudes greater than 50 degrees magnetic in the northern hemisphere . The geomagnetic storm contained a 1-hour growth phase, a 1-hour main phase, and a 4-hour decay phase. Four storm simulations were conducte d, corresponding to winter and summer solstices at both solar maximum and minimum. The simulations indicated the following: (1) O+ upflows t ypically occur in the cusp and auroral zone at all local times, and do wnflows occur in the polar cap. However, during increasing magnetic ac tivity, O+ upflows can occur in the polar cap, (2) The O+ upflows are typically the strongest where both T-e and T-i are elevated, which gen erally occurs in the cusp at the location of the dayside convection th roat, (3) The upward H+ and O+ velocities increase with T-e, which res ults in both seasonal and day-night asymmetries in the ion velocities, (4) During ''increasing'' magnetic activity, O+ is the dominant ion a t all altitudes throughout the polar region, (5) For solar minimum win ter, there is an H+ ''blowout'' throughout the polar region shortly af ter the storm commences (negative storm effect), and then the H+ densi ty slowly recovers. The O+ behavior is opposite to this. There is an i ncrease in the O+ density above 1000 km during the storm's peak (posit ive storm effect), and then it decreases as the storm subsides, and (6 ) For solar maximum summer, the O+ and H+ temporal morphologies are in phase; but the ion density variations at high altitudes are opposite to those at low altitudes. During the storm's peak, the H+ and O+ dens ities increase at high altitudes (positive storm effect) and decrease at low altitudes (negative storm effect).