New Approaches for Quantifying and Understanding Thermosphere Temperature Variability from Far Ultraviolet Dayglow

Abstract

The nonlinear and dynamic response of Earth’s thermosphere, and the embedded ionosphere, to highly variable forcing from the Sun and from the lower atmosphere is not completely understood. Current numerical models can represent climatological behaviors of the response to some extent, but their representation of weather-like variability of the thermosphere and ionosphere is far from adequate. This is in part due to limited observations of thermosphere states such as wind, temperature, and composition. Temperature is in particular a key prognostic variable of the upper atmospheric state that governs energetics, dynamics and chemistry of the ionosphere and thermosphere. Space-based nadir-viewing observations of the N2 Lyman-Birge-Hopfield (LBH) bands in the far ultraviolet (FUV) dayglow are an unique source of thermospheric temperature information because (1) they can determine temperature on Earth’s disk, providing significantly greater spatiotemporal coverage than current space-based limb-viewing and ground-based observations, and because (2) they are sensitive to temperatures at altitudes between ∼120−250 km that are otherwise difficult to access by other observational techniques.

Motivated by the National Aeronautics and Space Administration (NASA) Global-scale Observations of the Limb and Disk (GOLD) mission, this thesis explores new capabilities for probing temperature in the thermosphere with disk observations of Earth’s FUV dayglow. These new capabilities facilitate the interpretation and validation of thermospheric temperature derived from disk observations, and addresses current observational and modeling limitations by increasing the impact of the observations on the model’s ability to capture thermosphere temperature variability. Included in the new capabilities is FUV radiance data assimilation. Monitoring of Earth’s FUV dayglow from geostationary platforms, such as GOLD, signifies an opportunity to apply satellite radiance data assimilation, which has had a marked impact on the Numerical Weather Prediction (NWP) of the troposphere in the meteorological community, to the thermosphere.

The first part of the thesis begins with a thorough analysis of the thermosphere temperature information content in the LBH bands. This analysis produces two new estimation techniques to maximize the extraction of thermosphere temperature information from disk observations of LBH emissions. The first technique focuses on utilizing temperature information coming only from the observation while the second technique also incorporates prior information of the vertical temperature structure. These techniques are applied to GOLD radiance disk data and their capabilities are compared to current capabilities. The second part of the thesis is concerned with the development of the FUV satellite radiance data assimilation capability and the demonstration of this capability using GOLD data and whole atmosphere NWP tools. From one perspective, this is an extension of the capabilities developed in the first part of the thesis. From another perspective, this represents a paradigm shift in how observations from both Heliophysics observing systems and Earth observing systems are used in synthesis toward a comprehensive numerical prediction of the whole atmosphere that better represents the dynamic response of Earth’s thermosphere to the lower atmosphere forcing.