Open magnetic flux and magnetic flux closure during sawtooth events

We use IMAGE-FUV observations of the polar aurora and measurements of the ionospheric convection from the SuperDARN radar network to study several sawtooth events previously reported in the literature. We estimate the amount of open magnetic flux in the Earth magnetosphere during a significant part of these sawtooth intervals as well as the magnetic flux opening and closure rates, that is, the dayside and nightside reconnection rates. We find that during the sawtooth intervals the magnetosphere is highly loaded with open flux as a result of the strongly southward IMF carried by the solar wind during these intervals. The magnetosphere tries to relax to a less loaded configuration through a sequence of substorm expansions. However, these substorms do not necessarily evolve to their end before reintensification of nightside reconnection occurs in response to continued loading of the magnetosphere on the dayside. Citation: Hubert, B., S. E. Milan, A. Grocott, S. W. H. Cowley, and J. C. Gerard (2008), Open magnetic flux and magnetic flux closure during sawtooth events, Geophys. Res. Lett., 35, L23301, doi:10.1029/2008GL036374.