According to current understanding Sudden Commencements (SC) in magnetometer records are caused by a sudden compression of the magnetosphere by shocks (dynamic pressure steps) in the solar wind. So far SCs have mainly be studied with the help of magnetometer arrays, only very few systematic studies with satellite borne magnetometers have been published. We present a systematic study of 30 SCs observed by CHAMP on the night side (between 18 and 06 MLT) at low mid- latitudes (between -45° and +45° MLat) between July 2000 and December 2006. CHAMP is a polar orbiting satellite (87.25° inclin.) cruising at altitudes between 360 and 430 km. The SCs are recorded with the onboard fluxgate magnetometer and identified after subtracting the main magnetic field. For comparison, ground-based magnetometer records with 1-s time resolution from stations close to the satellite track have been used. During night-time, effects of ionospheric currents on the magnetic field are believed to be negligible, thus the SC magnetic signature represents only the effect of magnetospheric compression. The shape of the magnetic field step should therefore look very similar at satellite altitudes and on the ground. We demonstrate this with three (out of our 30 analysed) events observed at different geographical locations. Moreover, the magnitude of the magnetic field step is clearly related to the step size in the solar wind dynamic pressure.

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Schlegel, K.; Lühr, H.; Rother, M.; Yumoto, K. (2008): Night-time Sudden Commencements observed with CHAMP and Ground-based Magnetometers. 12th International Symposium on Equatorial Aeronomy (ISEA12) (Heraklion, Crete, Greece 2008).