Increases in the solar ultraviolet flux (&lgr;<1250¿) over the past five years of rising solar activity have been larger than anticipated. This increase in UV flux dramatically affects the production of ionization of the various constituents in the thermosphere. In this paper we use measurements of the solar UV flux by the Atmosphere Explorer satellites to determine ionization frequencies for the major thermospheric species for various dates exhibiting notably different levels of solar activity. For the convenience of users of such data, a reduced set of cross section and flux data is presented for the wavelength range below 1027 ¿, comprising 37 wavelength intervals.