Modeling Solar Eclipses at Extreme Ultra Violet Wavelengths and the Effects of Nonuniform Eclipse Shadow on the Ionosphere-Thermosphere system

Abstract

The impacts of solar eclipses on the ionosphere-thermosphere system particularly the composition, density, and transport are studied using numerical simulation and subsequent model-data comparison. We introduce a model of a solar eclipse mask (shadow) at Extreme Ultra Violet (EUV) wavelengths that computes the corresponding shadowing as a function of space, time, and wavelength of the input solar image. The current model includes interfaces for Solar Dynamics Observatory (SDO) and Geostationary Operational Environmental Satellites (GOES) EUV telescopes providing solar images at nine different wavelengths. We show the significance of the EUV eclipse shadow spatial variability and that it varies significantly with wavelength owing to the highly variable solar coronal emissions. We demonstrate geometrical differences between the EUV eclipse shadow compared to a geometrically symmetric simplification revealing changes in occultation vary $\pm$20\%. The EUV eclipse mask is validated with in-situ solar flux measurements by the PROBA2/LYRA instrument suite showing the model captures the morphology and amplitudes of transient variability while the modeled gradients are slower. The effects of spatially EUV eclipse masks are investigated with Global Ionosphere Thermosphere Model (GITM) for the 21 August 2017 eclipse. The results reveal that the modeled EUV eclipse mask, in comparison with the geometrically symmetric approximation, causes changes in the Total Electron Content (TEC)