Toward predicting the position of the magnetopause within geosynchronous orbit

Although the average magnetopause is similar to 10 RE from the Earth, the m agnetopause moves inside the geosynchronous orbit during extreme solar wind conditions. Under these circumstances some geosynchronous satellites sudde nly enter the magnetosheath and are exposed to the plasma and fields of the magnetosheath. In this study we evaluate the predictive capabilities of ma gnetopause location models in forecasting geosynchronous magnetopause cross ings. We predict periods during which geosynchronous satellites enter the m agnetosheath using the Petrinec and Russell [1996] and Shue et al. [1998] m agnetopause location models driven by data from Interplanetary Monitor Plat form (IMP) 8. These predictions are then verified with in situ observations from Geosynchronous Operational Environment Satellite (GOES) 5, 6, and 7. We estimate the false alarm rate, probability of detection, and probability of false prediction for the two models. The estimation shows that false al arm rate for a forecast with a 20-min separation cadence is similar to 62% (80%) for the Shue et al. [1998] model (the Petrinec and Russell [1996] mod el). The probability of detection is very high for both prediction models. These results suggest that both models work well in predicting magnetosheat h periods for geosynchronous satellites. Predictions from the models provid e a prerequisite condition for geosynchronous magnetopause crossings. Furth er examination of unsuccessful events indicates that preconditioning by the interplanetary magnetic field B-z needs to be included in the forecasting procedure for a better forecast. This finding provides us with a guide to i mproving future magnetopause location models.