Ionospheric Response for the Sept. 24-25, 1998 Magnetic Cloud Event

Heavy ionospheric ions play a crucial part in the overall space weather environment, particularly in the generation of high energy particle populations during disturbed periods. Multi-fluid global simulations are used to quantify the ionospheric outflows during the Sept 24-25, 1998 magnetic cloud event. The model results show that jumps in dynamic pressure associated with structures within the magnetic cloud lead to a temporary broadening of the cusp/cleft region and enhancements in the ionospheric outflows both in latitude and local time in association with dayside brightenings seen in Polar UVI observations. However, the inferred power in UVI is several times greater than that in the model outflows. After about 15 mins the cusp/cleft region in the model decreases to the nominal size of about 1-2 hrs in local time and a few degrees in latitude in conjunction with an overall decline in UVI intensity, and the energy fluxes are comparable. During the period of B(y) dominated IMF, the cleft ion fountain is seen in the model to reach 50-70 R(E) into the tail. For southward IMF period, the cleft ion fountain is restricted to less than about 20 R(E) into the tail, but convection around the flanks still leads to significant ionospheric mass loading in the deep tail.