COMPARISON OF IONOSPHERIC ELECTRICAL CONDUCTANCES INFERRED FROM COINCIDENT RADAR AND SPACECRAFT MEASUREMENTS AND PHOTOIONIZATION MODELS

Height-integrated electrical conductivities (conductances) inferred fr om coincident Sondrestrom incoherent scatter radar and DMSP-F7 observa tions in the high-latitude ionosphere during solar minimum are compare d with results from photoionization models. We use radar and spacecraf t measurements in combination with atmospheric and ionospheric models to distinguish between the contributions of the two main sources of io nization of the thermosphere, namely, solar UV/EUV radiation and auror al electron precipitation. The model of ROBINSON et al. (1987, J. geop hys. Res. 89, 3951) of Pedersen and Hall conductances resulting from e lectron precipitation appears to be in accordance with radar measureme nts. Published models of the conductances resulting from photoionizati on that use the solar zenith angle and the solar 10.7-cm radio flux as scaling parameters are, however, in discrepancy with radar observatio ns. At solar zenith angles of less than 90', the solar radiation compo nents of the Pedersen and Hall conductances are systematically overest imated by most of these models. Geophysical conditions that have some bearing on the state of the high-latitude thermosphere (e.g. geomagnet ic and substorm activity and a seasonal variation of the neutral gas d istribution) seem to influence the conductivity distribution but are t o our knowledge not yet sufficiently well modelled.