Understanding Magnetotail Drivers of Auroral Acceleration Using Polar/FAST Conjunction Data and Simulation Modeling

The formation of parallel electric fields in the auroral zone and subsequent particle acceleration is thought to be due ultimately to processes that occur in the magnetotail. A study is made to examine the magnetotail drivers of auroral processes using data from the Polar and Fast Auroral SnapshoT (FAST) satellites when the two are near magnetic conjunction in the auroral zone. Large scale kinetic simulations are used along with the satellite data to examine the physics of parallel electric fields as caused by magnetotail input at high altitudes. The results indicate that field-aligned currents, high-energy particle beams, and electromagnetic Alfven wave energy that flows earthward from the magnetotail all drive auroral processes. These different drivers operate at different times and latitude locations depending on magnetic activity level. The different drivers tend to result in different types of parallel electric fields in the auroral zone, which then cause different types of electron and ion parallel particle acceleration. The details of magnetosphere-ionosphere coupling that occurs in the auroral zone in terms of cause and effect will be discussed.