Characteristics of storm sudden commencement at geostationary orbit

Eighty‐one storm sudden commencements (ssc) observed on board GOES satellites at geostationary orbit are used to examine the local time variation of ssc amplitude. It is found that ssc amplitudes at synchronous altitude have a strong local time dependence in contrast to previous observations in the magnetosphere. Amplitude ratios (satellite amplitude/ground amplitude) are larger than unity in most cases observed in the daytime during 0600–1500 LT. The ssc amplitude tends to become very small near midnight as compared with that on the ground. Even a decrease in total force sometimes occurs in the midnight region. This means that magnetic compression does not always occur in the magnetic equator near synchronous orbit. The implication of these ssc characteristics are discussed in relation to ssc‐associated phenomena.