“…Above 130 km the ratio of the ion-neutral collision frequency to the ion gyrofrequency is too low for the technique to be reliable. PFRR also hosts an array of scanning Doppler interferometers (SDI) measuring both 630.0 nm (F-region) and 557.7 nm (E-region) neutral winds, and studies combining SDI winds and PFISR ion temperatures have been extremely valuable for studies of Joule heating [Anderson et al, 2013;Kiene et al, 2019]. For ion-neutral coupling studies at lower altitudes, PFRR supports a Rayleigh lidar that provides neutral temperature measurements in the stratosphere and mesosphere, a Na-resonance lidar that provides temperatures and winds in the 80-105 km region, and a VHF meteor radar that provides winds in the E-region.…”