Extraction of solar and thermospheric information from the ionospheric electron density profile

This exploratory study of ionospheric electron density N-e profile assimila tion concerns the extraction of information on exospheric temperature T-ex, atmospheric composition [O] and [N-2], meridional thermospheric winds, and solar EUV flux. These parameters are used as input variables to an ionosph eric model and adjusted, one, two, or three at a time, to bring the model N -e profile into best agreement with an experimental N-e profile. The import ant ambiguity/uniqueness issue in the multiple-variable fit, which has yet to be addressed in the literature, is discussed. We found the following: (1 ) In a single-variable fit, any variable tested may be adjusted successfull y to improve the data-model fit, but the validity of the derived variable g enerally depends on the validity of the values chosen for the fixed paramet ers. (2) The best fit model profile from a single-variable fit sometimes sh ows clear differences from the measured profile, indicating that multiple-v ariable fitting is warranted. The multiple-variable fit often greatly reduc es the model-data profile differences and improves the error bars on the de rived parameters. (3) Multiple-variable fits often show large variable corr elations, indicating that variable determination is often not unique. (4) T he meridional wind often shows weak correlation with other variables, sugge sting that the meridional wind and any other parameter can be reliably extr acted, provided that the other atmospheric variables are known. (5) [N-2] o ften shows strong correlation with other parameters (except with the wind). The EUV flux and [O] also show large correlation. (6) The T-ex-[O] and T-e x-EUV pairs show medium to high correlation. (7) The three-variable fits ne arly always show large ambiguities in the derived parameters.