Ionospheric data assimilation: Comparison of extracted parameters using full density profiles and key parameters

This paper explores the relative accuracy of deriving solar EUV flux, exospheric temperature Tex, and meridional winds using complete altitude profiles of ionosphere electron density as compared to just using key parameters such as Nmax, hmax and ionospheric electron content. Incoherent scatter radar observations at Millstone Hill and Shigaraki and an ionospheric model are used in this study. We can make the following points: (1) With either the profile or key parameter data, the EUV flux can be inferred with little ambiguity, given that background variables such as the meridional wind are known. (2) The southward wind and Tex can be simultaneously derived from either type of data. The results, in particular the [O]/[N2] results, are similar for the two types of data. The accuracy of the wind result relies much on the accuracy of hmax as well as the geomagnetic dip angle. (3) A few key ionospheric parameters are not always sufficient to give a unique definition of ionospheric conditions. Additional parameters or even a full profile data are sometimes needed. In general, however, the key parameter pair hmaxNmax seems to be a suitable assimilation data source, at least for retrieving the local features of the Tex and meridional wind variation.