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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   R E d − 1 , while the average expansion rate was ∼ 0.4   R E d − 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. [ABSTRACT FROM AUTHOR]

The investigation of heavy ions dynamics and properties in the Earth's magnetosphere is still an important field of research as they play an important role in several space weather aspects. We present a statistical survey of the average ion mass in the dayside magnetosphere made comparing plasma mass density with electron number density measurements and focusing on both spatial and geomagnetic activity dependence. Field line resonance frequency observations across the European quasi-Meridional Magnetometer Array, are used to infer the equatorial plasma mass density in the range of magnetic L-shells 1.6–6.2. The electron number density is derived from local electric field measurements made on Van Allen Probes using the Neural-network-based Upper-hybrid Resonance Determination algorithm. The analysis is conducted separately for the plasmasphere and the plasmatrough during favorable periods for which both the plasma parameters are observed simultaneously. We found that throughout the plasmasphere the average ion mass is ≃1 amu for a wide range of geomagnetic activity conditions, suggesting that the plasma mainly consist of hydrogen ions, without regard to the level of geomagnetic activity. Conversely, the plasmatrough is characterized by a variable composition, highlighting a heavy ion mass loading that increases with increasing levels of geomagnetic disturbance. During the most disturbed conditions, the average radial structure shows a broad maximum around 3–4 Earth radii, probably correlated with the accumulation of oxygen ions near the plasmapause. Those ions are mostly observed in the post-dawn and pre-dusk longitudinal sectors. [ABSTRACT FROM AUTHOR]

This paper presents how the magnetosphere–plasmasphere–ionosphere system was affected as a whole during the geomagnetic storm peaking on 27 May 2017. The interplanetary conditions, the magnetospheric response in terms of the magnetopause motion, and the ionospheric current flow pattern were investigated using data, respectively, from the WIND spacecraft, from GOES15, GOES13, THEMIS E, THEMIS D and THEMIS A satellites and from the INTERMAGNET magnetometer array. The main objective of the work is to investigate the plasmaspheric dynamics under disturbed conditions and its possible relation to the ionospheric one; to reach this goal, the equatorial plasma mass densities derived from geomagnetic field line resonance observations at the European quasi-Meridional Magnetometer Array (EMMA) and total electron content values obtained through three GPS receivers close to EMMA were jointly considered. Despite the complexity of physical mechanisms behind them, we found a similarity between the ionospheric and plasmaspheric characteristic recovery times. Specifically, the ionospheric characteristic time turned out to be ~ 1.5 days, ~ 2 days and ~ 3.1 days, respectively, at L ~ 3, L ~ 4 and L ~ 5, while the plasmaspheric one, for similar L values, ranged from ~ 1 day to more than 4 days. [ABSTRACT FROM AUTHOR]