Book Description

In support of the Global Weather Central of the Air Weather Service, we have developed computer techniques to determine, in near real time, the equatorward boundary of the auroral oval using the data from the SSJ/3 sensors flown on board the DMSP satellites. The boundary is determined on both the morning and evening sides of the oval and in both northern and southern auroral zones. Three tests are used in the boundary determination, one on the evening side and two on the morning side of the auroral oval. On the evening side of the auroral zone, since low energy particles always are observed at the lowest latitude, the boundary is determined by testing the summed counts in the six channels of the SSJ/3 detector covering the energy range from 110 eV to 1000 eV. The boundary is chosen when the summed counts exceed 30 for 3 successive seconds. The data are always tested as a function of increasing magnetic latitude. On the morning side, high energy electrons are always observed first. Since the channels measuring high energy electrons may be contaminated by penetrating particles from the ring belts, two tests are required. The first test picks the boundary at the point where three successive ratios of 4-sec averages of channel 8 to channel 9 are less than 5. The second test chooses the boundary where the ratio of the summed counts in channels 1 through 4 of the SSJ/3 sensor to channels 5 through 8 exceeds 1.5 or is less than 0.5 for 3 successive seconds.