An Empirical Model for the Dayside Magnetospheric Plasma Mass Density Derived From EMMA Magnetometer Network Observations

A local time dependent empirical model of the equatorial plasma mass density in the inner magnetosphere is derived from field line resonance (FLR) observations at the European quasi-Meridional Magnetometer Array (EMMA). Models of the plasmasphere, plasmatrough, and plasmapause are derived separately and then combined. The whole model is limited to the local time (LT) sector 06:00-18:00 and to the range of equatorial distances 2.3 R-E < r(eq) < 8 R-E. It is also dependent on the geomagnetic activity but only in determining the plasmapause position. It well describes the recovery phase following a plasmasphere erosion but is not intended to reproduce highly dynamical phases. The plasmasphere model is limited to the range 2.3 R-E < r(eq) < 4.5 R-E and predicts a mass density increase in the daytime sector (10-18 LT) which becomes more evident with increasing L (up to a factor of similar to 2). A comparison with previous models of plasmaspheric electron density suggests that the diurnal variation is mainly contributed by the heavy ions. The plasmatrough model is limited to the range 3.8 R-E < r(eq) < 8 R-E and predicts a diurnal variation even more pronounced. Comparison with electron density models suggests that the average ion mass density can increase from similar to 2.0 to similar to 4-5 amu during daytime hours. An automated algorithm to search for plasmapause signatures in the radial mass density profiles derived from experimental observations is also presented. It could represent a useful space weather tool when included in a real-time monitoring system of the plasmasphere.