Temperatures and collision frequency in the polar <i>E</i> region measured with the incoherent scatter technique

Incoherent scatter measurements with a range resolution of 3.0 km have been performed at the facility at Chatanika, Alaska, between 90‐ and 120‐km altitude. From the shape of the measured autocorrelation function, values for the ion‐neutral collision frequency, the electron temperature, and the ion temperature have been deduced. During quiet conditions the obtained quantities do not significantly deviate from the Cira model, whereas during particle precipitation events the temperatures are increased. The measurements also show that, contrary to common assumptions, during disturbed conditions the electron to ion temperature ratio is significantly greater than unity between 100 and 110 km. Below about 95 km the results indicate that coherent reflections from D region electron density gradients or possibly ground clutter become important. This leads to correction factors for electron density measurements at those heights.