Modelling the interaction of poloidal Pc5 waves with the high-latitude ionosphere (Invited)

Abstract:

A 2D multi-fluid wave model is used to interpret EISCAT observations of poloidal Pc5 waves as they interact with the ionosphere. The wave model describes the full interaction of waves with a dynamic ionosphere that is prescribed using the IRI2007 model. Neutral species are incorporated using the MSIS86 model. The event of interest is described by Lester, Davis, and Yeoman [Annalles Geophysicae, vol 18, p.257-261 (2000)], which shows variations of plasma density, electron and ion temperature, and meridional and azimuthal flows in the ionosphere due to Pc5 ULF waves. The observations suggest the wave has a compressional component indicative of a moderate to high azimuthal wavenumber. In order to reproduce the observations, two populations of precipitating electrons with different energies and time variations are introduced into the model. Constant high-energy precipitation is introduced to enhance the ionospheric conductivity to levels observed, while a pulsating low-energy population is introduced to explain the modulations in ionospheric plasma density and electron temperature that are observed. To obtain agreement with the observations, it was also necessary to adjust the phase shift between the Alfven wave and precipitating electrons. With these assumptions, the temporal evolution of the electron and ion temperatures, as well as the azimuthal flow velocity obtained in the simulation are similar to the observations. The simulation also reproduces the observed timing between electron density and electron temperature peaks. Without adjustments to the ionospheric model, it is found that the rate of decay of electron density spikes after the precipitation pulse is over is insufficient to return the electron density to its initial value. The major role in the decay of electron density ehancements is found to be recombination, with the contribution from the convective term in the continuity equation playing only a minor role. It is found that by increasing the N2 density sufficiently in the ionosphere, the recombination rate can be enhanced to a point where the electron density decays in agreement with the observations. The conclusion from our wave modelling is that in conjunction with ground observations such models can shed light on Pc5 wave generation and precipitation processes in the magnetosphere.