UV Limb Scan and X-Ray Occultation Soundings of Thermospheric Density

The Naval Research Laboratory flew the Unconventional Stellar Aspect (USA) and High Resolution Airglow and Aurora Spectrograph (HIRAAS) experiments aboard the Advanced Research and Global Observation Satellite (ARGOS) during 1999--2002. USA was a collimated proportional counter X-ray telescope with a large collecting area and microsecond time resolution for 1--10 keV astronomical observations. Additionally, by acquiring occultation spectra of celestial objects USA measured total atmospheric density in the Earth's mesopause and lower thermosphere regions (80--130~km). HIRAAS was a suite of three middle-, far- and extreme-ultraviolet spectrographs for performing limb scan measurements of the Earth's thermosphere and ionosphere (100--750~km). HIRAAS and USA operated simultaneously and were mounted on the same side of the ARGOS spacecraft, enabling novel UV and X-ray studies of the Earth's atmosphere. We present atmospheric density retrievals using simultaneous X-ray and UV measurements from 2000 and compare the results with climatological thermosphere models. The consistency, complementarity, and accuracy of the datasets are discussed, along with relevant space weather considerations, such as the effects of solar X-ray flares upon lower thermosphere structure.