Semi-Empirical, First-Principles, and Hybrid Modeling of the Thermosphere to Enhance Data Assimilation

Abstract

Abstract : During this task, we established a method for extracting the most significant basis functions from a physics-based model of thethermosphere and ionosphere. A new model was then constructed by replacing the spherical harmonic functions used in an existing semi-empirical thermosphere model with these basis functions. The resulting hybrid model, published in the Space Weather Journal,demonstrated the ability to represent sparse thermospheric data in a more accurate and efficient way. In addition, we chose Jacchia 1970 asour underlying semi-empirical model so that the new hybrid model functions as a direct replacement for the High Accuracy Satellite Drag Model used by AFSPC and the JSpOC. We also worked to improve the hybrid model by investigating the limitations of and possible improvements to the underlying assumptions imposed by the chosen models. In particular, we realized that there was a large and potentially significant component missing from all general circulation models, that being the appropriate treatment of helium in the upper thermosphere. To rectify this situation, we undertook the project of adding helium to the solution of a first-principles community model of the thermosphere and ionosphere. In doing this, we discovered that this could only be done self-consistently by solving for helium as a major species, as opposed to as a minor species. The product of this work was the first physics-based model to accurately simulate the seasonal and latitudinal behavior of the helium distribution. This work was published in the Journal of Geophysical Research.