Availability of far ultraviolet observations of Earth’s dayglow by the NASA Global-scale Observations of the Limb and Disk (GOLD) mission presents an unparalleled opportunity for upper atmosphere data assimilation. Assimilation of the observed dayglow emissions can be formulated in a similar fashion to lower atmosphere radiance data assimilation approaches using the sensitivity of the Lyman-Birge-Hopfield (LBH) band emission to thermospheric temperature. To demonstrate such an approach, we present a proof-of-concept implementation of an ensemble square-root filter measurement update step using ensemble simulation of the thermosphere and LBH emission by the NOAA’s Whole Atmosphere Model (WAM) and NCAR’s Global Airglow model. With help of a new assimilation approach, the utility of GOLD observations can be extended to reveal the global, time-dependent, altitude-resolved thermospheric structure, offering the key to addressing a number of outstanding questions such as origins of traveling atmospheric disturbances.

Earth’s thermosphere is driven by a combination of meteorological, magnetospheric, and solar forcing that exhibits significant variation from day-to-day. The relative importance of these drivers and their combined affects in determining daily thermospheric variability on global and local scales is an important science question particularly under solar minimum conditions. Far-ultraviolet, satellite-based airglow observations are a valuable tool to probe the thermosphere and can provide the spatial coverage and temporal resolution required to improve our understanding of thermospheric day-to-day variability in response to driver variability. This paper presents first results from principal component analysis and ensemble sensitivity analysis to quantify the major modes of dayglow variability in both OI 135.6 nm emissions and N2 Lyman-Birge-Hopfield emissions and the sensitivity of these modes to geomagnetic and lower atmosphere drivers. The ensemble simulations are performed with NOAA’s Whole Atmosphere Model that extends from Earth’s surface to the exobase and NCAR’s Global Airglow Model for a recent period with low-to-moderate levels of geomagnetic activity and low solar activity. The ensemble simulations are compared to thermospheric observations over the same period by the NASA Global-scale Observations of the Limb and Disk (GOLD) mission.