Typical and Atypical Magnetospheric Response to Sudden Solar Wind Dynamic Pressure Changes

Friday, 19 December 2014
C. Robert Clauer1, Elena Semenovna Belenkaya2, Igor I Alexeev2, Vladimir V Kalegaev3, Daniel T Welling4 and Xia Cai5, (1)National Institute of Aerospace, Hampton, VA, United States, (2)Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, Moscow, Russia, (3)Moscow State University, Moscow, Russia, (4)University of Michigan, Ann Arbor, MI, United States, (5)Virginia Tech, Hampton, VA, United States
A sudden increase in solar wind dynamic pressure will cause a compression of the magnetosphere that is observed as a sudden jump in the low latitude surface geomagnetic field. We show here that this reaction may depend on conditions in the IMF and in the magnetosphere/ionosphere system. The typical response of the low-latitude northward magnetic field is a simultaneous global increase, generally call a SI (sudden impulse) or SSC (storm sudden commencement) if a geomagnetic storm follows. We have found several atypical cases, however, for which the largest positive disturbances are observed on the night side and little or no field increase is registered near local noon. For some of these cases the solar wind pressure change is simultaneous with a northward turning of the IMF from near zero Bz . Another case is shown where the pressure change follows a period of increasing negative IMF Bz. We propose that the magnetic response for the atypical cases can be accounted for by a transition current system where the ionospheric closure of the current system depends upon the auroral conductivity established by previous activity.