Plasmasphere Refilling after the 1 June 2013 Geomagnetic Storm

Plasma content and distribution are key parameters in the dynamics of the inner magnetosphere. The plasmasphere contributes, for the most part, to the plasma mass density, and its properties are very dependent on the history of the magnetosphere and geomagnetic activity. In this work, we investigated plasmasphere dynamics and plasmasphere–ionosphere coupling, focusing on the refilling process that followed the geomagnetic storm that occurred on 1 June 2013. The equatorial plasma mass density used to evaluate the refilling rates was remotely sensed by observation of the field line resonance (FLR) frequencies of the geomagnetic field, driven by ultra-low-frequency magnetic waves. The FLR frequencies were retrieved by performing an analysis of signals detected by several station pairs of the European quasi-Meridional Magnetometer Array. We estimated the rate at which the refilling process occurred, concentrating on both the diurnal and the day-to-day refilling rates. The estimated contraction rate during the main phase of the storm was higher than ∼3.5 REd−1, while the average expansion rate was ∼0.4 REd−1. We investigated the radial dependence of the refilling rates, using a novel approach based on fit plasma mass density profiles, and we related their variation to the plasmasphere boundary layer and the zero-energy Alfvén boundary. We found evidence supporting the idea that flux tubes mapping in the region between these two boundaries experience an enhanced refilling process.