ON THE PHYSICS OF STRONG MAGNETIC STORMS

1. ON THE PHYSICS OF STRONG MAGNETIC STORMS • Motivation: Experimental observations indicate that the basic physics controlling substorm dynamics under strong solar wind conditions (VBz> 5 mV/m) is significantly different than under weak and moderate conditions. Key indication of such behavior is the observed saturation of the polar cap potential. Current MHD codes while describing with relative accuracy substorm effects under moderate conditions fail to predict the growth of the polar cap potential under strong conditions. • Objectives: To incorporate in the LFM code nonlinear physics due to anomalous E-region heating that becomes critical under strong solar wind conditions. • Status: The theory of the anomalous E-region heating and the associated nonlinear modification of the ionospheric conductance has been completed. A nonlinear algorithm has been derived and incorporated in the LFM model. A number of test runs of the modified LFM code clearly indicate saturation of the polar cap potential consistent with the data. Work is continuing with emphasis on the consequences of the new effect on the overall behavior of the magnetosphere for strong storms.

2. SAMPLE RESULTS (a) (b) (c) Simulations of Jan. !0, 1997 storm. Comparison of LFM results with data for the polar cap potential with and without anomalous heating (a). Pedersen conductance without (b) and with (c) anomalous heating