ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-30-927-2012 On the relaxation of magnetospheric convection when <I>B</I><sub>z</sub> turns northward Kelley M. C. 1 School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA 04 06 2012 30 6 927 928 Copyright: © 2012 M. C. Kelley 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/30/927/2012/angeo-30-927-2012.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/30/927/2012/angeo-30-927-2012.pdf

The solar wind inputs considerable energy into the upper atmosphere, particularly when the interplanetary magnetic field (IMF) is southward. According to Poynting's theorem (Kelley, 2009), this energy becomes stored as magnetic fields and then is dissipated by Joule heat and by energizing the plasmasheet plasma. If the IMF turns suddenly northward, very little energy is transferred into the system while Joule dissipation continues. In this process, the polar cap potential (PCP) decreases. Experimentally, it was shown many years ago that the energy stored in the magnetosphere begins to decay with a time constant of two hours. Here we use Poynting's theorem to calculate this time constant and find a result that is consistent with the data.

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