Monte Carlo computations of F-region incoherent radar spectra at high latitudes and the use of a simple method for non-Maxwellian spectral calculations

Monte Carlo simulations of ion velocity distributions in the high-latitude F region have been performed in order to improve the calculation of incoherent radar spectra in the auroral ionosphere. The results confirm that when the ion temperature becomes large due to frictional heating in the presence of collisions with the neutral background constituent, F region spectra evolve from a normal double hump, to a triple hump, to a spectrum with a single maximum. An empirical approach is developed to overcome the inadequacy of the Maxwellian assumption for the case of radar aspect angles of between 30 and 70 deg.