Mapping PI2 Pulsations from the Ground to the Plasma Sheet: Results from UCLA and Lyon-Fedder-Mobarry Global MHD Simulations

Abstract:

The relationship between the onset of Pi2 pulsations in mid-latitude ground magnetometers and substorm onset has been used extensively over the years to determine when and where substorm onset takes place. In order to understand how Pi2 pulsations are generated in the magnetotail and how they propagate into the ionosphere, we have modeled a substorm on August 25, 2013 using both the UCLA and the Lyon-Fedder-Mobarry (LFM) 3D global magnetohydrodynamic (MHD) models. By mapping from virtual ground stations into the plasma sheet we are able to determine what the specific magnetospheric drivers in the simulation are for Pi2 period fluctuations observed at different locations in the ionosphere.

The results from both simulations show that Pi2 period pulsations develop in the plasma sheet in the magnetic field, velocity, and pressure, concurrently with the arrival of fast earthward flows and their associated dipolarization fronts. When we map in the UCLA model from the ionosphere to locations in the plasma sheet where the flow channels are present, perturbations are not evident in the ionosphere, but there are Pi2 period perturbations at the inner edge of the MHD region of the simulation (~3 RE) in the magnetic field components, thermal pressure and density. The LFM ionosphere is much more dynamic than the UCLA ionosphere for this event. Field lines from locations in the ionosphere where PI2 are observed that map to flow channels in the plasma sheet show Pi2 period perturbations in the parallel currents in the ionosphere which match very well with the velocity and magnetic field perturbations in the plasma sheet.