Statistical relationships between cosmic radio noise absorption and ionospheric electrical conductances in the auroral zone

[1] Statistical models expressing the Hall and Pedersen conductances and their ratio as functions of cosmic noise absorption (CNA) are derived for five intervals of magnetic local time (MLT). The models are based on simultaneous measurements of electron densities from the European Incoherent Scatter UHF radar at Tromsø (69.6 N, 19.2 E) and absorption from the imaging riometer at Kilpisjärvi (69.1 N, 20.8 E). The Hall conductance and the conductance ratio are found to be rather strongly related to CNA, whereas the Pedersen conductance is less so. The Hall conductance-CNA relationship is strongly dependent on MLT. These results are interpreted as being the consequence of the particular sensitivity of CNA to the typical energy of electron precipitation, the latter changing as a function of MLT as the electrons drift around the Earth. The models are compared to a previous study which did not use simultaneous measurements or take into account the MLT dependence. There is a significant difference between that study and the results presented here.