Remote Sensing of Equatorial Mass Density via Virtual Ground-Based Magnetometers in the SWMF Global Magnetospheric Model

Abstract:

The resonant frequencies of standing Alfven waves (field line resonances, or FLRs) depend on the equatorial mass density distribution. We can identify field line resonances using cross-phase spectra and power spectral densities, and the equatorial mass density distribution can be extracted from the frequency assuming an axisymmetric and power law distribution along dipolar field lines. Here we report the use of arrays of virtual ground-based magnetometers in two simulations ran in the SWMF global magnetospheric model to remotely sense equatorial mass density. First we confirm that SWMF reproduces a multi-harmonic distribution of FLRs in the dayside magnetospheric cavity, and then we determine the time-dependent resonant frequency from an analysis of the short-time power spectral density and cross-phase spectra of the magnetic vector fields from meridianal chains of virtual ground-based magnetometers. We show that this technique can accurately measure the spatiotemporal evolution of mass density within the simulations by comparing the FLR inferred densities with the in situ data. This is the first such attempt at using virtual ground-based magnetometers in a self-consistent, three-dimensional, coupled global magnetospheric and ionospheric model to remote sense the equatorial mass density.