The relationship between DSCS III sunlit surface charging and geomagnetic activity indices

The authors report on a survey of correlations between DSCS III satellite sunlit surface charging data and tabulated values of selected geomagnetic activity indices. This study is driven by the motivation to find a set of indices that have the potential to be used as proxies for determining the presence (nowcasting) and likely onset (forecasting) of surface charging. DSCS III data were compared with the Dst, ap, and the Polar Cap indices for a study period covering day 229, 1995 through day 115, 1999. Results show that: (1) significant correlations (R²>0.97) between average frame charging level and all three geomagnetic activity indices exist, and (2) the probability of charging events increases monotonically with increasing levels of geomagnetic activity until extreme levels are approached. It is postulated that during these extreme geomagnetic events, an anomalous source of neutralizing ions may be present at geosynchronous orbit either due to direct input from the solar wind or to ion outflow from the ionosphere