Publication Date:
2019
Description:
Abstract
We analyze three substorms that occur on 1) 9 March 2008 05:14 UT, 2) 26 February 2008 04:05 UT, and 3) 26 Feb 2008 04:55 UT. Using ACE solar wind velocity, IMF Bz values, we calculate the rectified (southward Bz) solar wind voltage propagated to the magnetosphere. The solar wind conditions for the two events were vastly different, 300 kV for 9 March 2008 substorm, compared to 50 kV for 26 February 2008. The voltage is input to a nonlinear physics based model of the magnetosphere called WINDMI. The output is the westward auroral electrojet current which is proportional to the auroral electrojet (AL) index from WDC Kyoto and the SuperMAG auroral electrojet index (SML). Substorm onset times are obtained from the superMAG substorm database, Pu et al. [2010], Lui [2011] and synchronized to THEMIS satellite data. The timing of onset, model parameters and intermediate state space variables are analyzed. The model onsets occurred about 5 to 10 mins earlier than the reported onsets. Onsets occurred when the geotail current in the WINDMI model reached a critical threshold of 6.2 MA for the 9 March 2008 event, while, in contrast, a critical threshold of 2.1 MA was obtained for the two 26 February 2008 events. The model estimates 1.99 PJ of total energy transfer during the 9 March 2008 event, with 0.95 PJ deposited in the ionosphere. The smaller events on 26 February 2008 resulted in a total energy transfer of 0.37 PJ according to the model, with 0.095 PJ deposited in the ionosphere.
Print ISSN:
2169-9380
Electronic ISSN:
2169-9402
Topics:
Geosciences
,
Physics
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