Sounding rocket data base of E- and D-region ion composition Original Research Article

Detailed in situ ion composition measurements in the E- and D- region ionosphere are available only from eccentric orbiting satellites with very low perigees and from sounding rockets. The lower limit for existing satellite data is about 130 km. Below this altitude mostly sounding rockets have sampled the ion composition. These sounding rocket data sets have been analyzed in the literature individually in the past on a case-by-case basis. In order to provide the best empirical picture possible of the lower ionosphere molecular ion distributions all available published sounding rocket observations of O2+ and NO+ ion concentrations were scanned and digitized to provide an empirical data base of the lower ionosphere. There were 43 such flights selected, which were scattered in latitude and local time. There were few low latitude observations, most of the measurements were made from middle and high latitude launch sites. The distributions are characterized at all latitudes by large drops in the concentrations from day to night with the molecular ion O2+ having the greatest range of variation above ∼ 100 km and NO+ below 90 km. Features of the sounding rocket data distributions at low latitudes, middle latitudes and at high latitudes and its limitations are discussed and the measurements compared with the International Reference Ionosphere (IRI) to investigate the accuracy of the IRI ion composition model in the lower ionosphere. The IRI ion composition model is based predominantly on dayside midlatitude observations for equinoctial and summer conditions. Our results show that winter nighttime measurements need to be expanded in order to improve the model.