Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence

We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15 km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, assumed to be caused by transient electric fields associated with velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin-Helmholtz instability will grow for the two presented cases.