The Breathing Plasmasphere: Erosion and Refilling

Global observations of He⁺ ions from the Imager for Magnetopause to Aurora Global Exploration mission Extreme Ultraviolet Imager are used to examine the dynamics of plasmasphere content using integrated mass through times of erosion and refilling for 1.5≤L≤5.5. Perhaps the most basic and important attributes of the plasmasphere are its mass and spatial distribution. However, our understanding is often constrained by the method of measurement. Storm time loss of plasmasphere content is a kind of exhalation where plasma is lost. Refilling or inhalation into the body of the plasmasphere occurs during the following calm. Using a follow the mass approach, storm time plasmasphere loss for 1.5≤L<5.5 is found to range from 32% to 62% during three events. Plasma lost inside the average eroded plasmapause boundary ranges from 22% to 42% and outside from 35% to 72%. Following the start of refilling, the innermost L shells show the lowest observed refilling rates. Mass refilling rates at higher L shells rise to a maximum observed ∼6 Mt/day near L = 4.5 that is less at higher L shells (Mt/d = 1,000 kg/day). More variability and higher refilling rates are found during lower solar activity. The mass content of the plasmasphere between L = 1.5 and 3.0 was also followed for 54 days when it exhibited eight "breathes." Using this analogy, only the first inhale/exhale is "deep." The remaining carry forward the consequences of past and continued activity that prevents full recovery. There appears to be a month long declining trend in the mass of the inner plasmasphere during the last two thirds of this time.