Ionospheric and Thermospheric Contributions in TIMED/GUVI O 135.6 nm Radiances

Abstract

AbstractWe developed an empirically determined, data‐driven method to extract the ionospheric and thermospheric contributions in the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (GUVI) 135.6 nm radiances on dayside to improve the O/N2 product. The technique assumes a reference dayside ratio of 130.4 and 135.6 nm radiances versus solar zenith angle (SZA) established from geomagnetically quiet observations and a fixed night side 130.4–135.6 nm radiance ratio of 1.2. The method effectively separates the ionospheric and thermospheric contributions in the observed 135.6 nm radiance. This not only improves the estimation of the thermospheric O/N2 ratio, (an important space weather parameter), by removing the ionospheric contribution in the GUVI 135.6 nm radiance data, but also provides the ionospheric signature in the 135.6 nm radiance. Comparison between GUVI ionospheric 135.6 nm radiances due to O+ and electron radiative recombination with coincident GPS TEC data shows a similar morphology of equatorial arcs, such as the arc latitude separation and nonmigrating tidal signature, confirming that the method is reliable. When there are no equatorial arcs, the ionospheric contribution is low, also consistent with low TEC data. This method can be applied to DMSP/SSUSI and other far ultraviolet data with simultaneous disk 130.4 and 135.6 nm measurements.