Plasmaspheric Loss Estimates

A significant amount of material can be removed from the plasmasphere during periods of enhanced geomagnetic activity. Magnetospheric convection acts to strip away the outer layers of the plasmasphere, and flux tubes in the inner plasmasphere may be significantly depleted as well. Using global images of the He⁺ distribution in the inner magnetosphere, we calculate the amount of He⁺ removed from a volume extending from 1.5 to 5.5 {R_E} during a set of five moderate disturbance periods. For each of the events, approximately 1 to 3 x 10³⁰ He⁺ ions were removed, which constituted between 20 and 42 % of the initial He⁺ distribution, in a period of 15 hours or less. The loss percentage is correlated with the number of hours of strongly southward IMF (B_z < -5 nT). Between 25 and 40 % of the He⁺ loss appears to occur from within the newly established plasmapause boundary. The total mass removed for each of the events is estimated to be in the range of 50 to 100 metric tons with variations on the order of tens of metric tons depending on the assumed value of the He⁺ to H⁺ density ratio.