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

The authors report on a survey of correlations between DSCS III satellite s unlit surface charging data and tabulated values of selected geomagnetic ac tivity indices. This study is driven by the motivation to find a set of ind ices that have the potential to be used as proxies for determining the pres ence (nowcasting) and likely onset (forecasting) of surface charging. DSCS III data were compared with the Dst, ap, and the Polar Cap indices for a st udy period covering day 229, 1995 through day 115, 1999. Results show that: 1) significant correlations (R-2 > 0.97) between average frame charging le vel and all three geomagnetic activity indices exist, and 2) the probabilit y of charging events increases monotonically with increasing levels of geom agnetic activity until extreme levels are approached. It is postulated that during these extreme geomagnetic events, an anomalous source of neutralizi ng ions may be present at geosynchronous orbit either due to direct input f rom the solar wind or to ion outflow from the ionosphere.