Ion-Neutral Coupling in Earth’s Thermosphere, Estimated from Concurrent Radar and Optical Observations above Alaska

Abstract

During March–April 2011 a campaign of coordinated observations was undertaken between the Poker Flat Advanced Modular Incoherent Scatter Radar and the Poker Flat Scanning Doppler Imager. These instruments provide horizontally resolved maps of plasma and neutral parameters in Earth’s thermosphere. We report on data collected during the campaign, and use these data to investigate two key aspects of ion–neutral coupling, namely Joule heating and the ion–neutral collision frequency. Volumetric Joule heating rates were often well correlated with measured ion temperature enhancements. The contribution of the neutral wind dynamo to the observed heating rates was positive when the absolute horizontal magnetic field perturbation (|ΔH|) was less than approximately 40 nT, and negative above that level. The total momentum–transfer ion–neutral collision frequency was estimated to be 1.02−0.152+0.179s−1 at an altitude of 260 km, which, for a neutral composition of 75% atomic oxygen, yielded an estimate of the O⁺–O collision frequency of 0.766−0.114+0.134s−1.