Study of D region ionosphere using incoherent scatter radar measurements

Within the recently started "HPC-approach to Ionospheric Situational Awareness (HISSA)" project, we will re-analyze a comprehensive set of existing European incoherent scatter radar (EISCAT) measurements from Tromso VHF radar carried out since 1990. Our special focus is to extract, for the first time, the spectral information of these experiments for the benefit of better understanding the potential long-term changes in the polar D-region ionosphere. Backscattered spectral parameters are estimated by fitting a theoretical autocorrelation function (ACF) to the observed data by using a Markov chain Monte Carlo (MCMC) inversion approach. The methodology and some preliminary results of the neutral temperature, electron density, and plasma drift velocity at D region altitudes will be presented. The temperature estimates from EISCAT VHF measurements are compared with the simultaneous LIDAR temperature measurements from Tromso. The challenges of D-region temperature estimates from incoherent scatter radar spectral parameters, which is a function of ion-to-neutral collision frequency and ion mass will be discussed in detail.