Simulations of Alfvén waves in the geomagnetic tail and their auroral signatures

Observations show that Ultra-Low Frequency (ULF) Alfven waves in the magnetotail have distinctive properties depending upon their location. In particular, those in the plasma sheet boundary layer (PSBL) have a larger amplitude and favor earthward propagation compared to those in the tail lobe which have the polarization of standing waves. The PSBL waves are also associated with electron acceleration and optical auroral emissions that exhibit equatorward motion. In this paper we present simulations of MHD wave coupling in the magnetotail to support an explanation for how Alfven waves with these properties may be established. The simulations also suggest the waves should have periods from 5 min to >20 min, and produce auroral emissions in the ionosphere having a latitudinal range of 40-130 km and equatorward speed of order 1 kms(-1). Field aligned currents are typically a few mu Am-2.