Sheared flows and small-scale Alfven wave generation in the auroral acceleration region

Coincident particle and optical measurements from the Reimei spacecraft suggest that sheared flows through an inverted-V arc may be unstable to the emission of Alfven waves. The particle measurements reveal time dispersed field-aligned electron bursts typical of low energy electrons accelerated by inertial Alfven waves (IAWs). These Alfven wave accelerated electrons are embedded within multi-keV inverted-V electron structures. The optical measurements at the footprint of the inverted-V structures reveal counter propagating and folded/vortical discrete auroral forms moving with speeds of similar to 14-18 km/s. We show that the flow shear inferred from this motion exceeds that required for instability to the emission of Alfven waves on scales of the order of an electron inertial length. The emission of these waves provides a likely means for driving the low energy dispersed electron bursts we observe. Citation: Asamura, K., et al. (2009), Sheared flows and small-scale Alfven wave generation in the auroral acceleration region, Geophys. Res. Lett., 36, L05105, doi:10.1029/2008GL036803.