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) in order of $\pm$20\%, 5-20\% in F-region plasma drift, and 20-30\% in F-region neutral winds.

Solar eclipses cause profound effects on ionosphere-thermosphere dynamics due to the abatement of solar Extreme Ultra Violet (EUV) irradiance. The reduced EUV flux cause relative reduction of ionospheric plasma density and temperature, and well as it reduces thermospheric temperature, and alters neutral winds. Numerical simulations are used to understand and characterize the ionosphere-thermosphere response to solar eclipses and to compare the model results with observations. The models have traditionally implemented simplified solar eclipses, assuming spherically symmetric models with the maximum eclipse (obscuration) set to ~15%. We present a realistic model of solar eclipses, using Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA) images of the solar corona. This model computes the eclipse occultation factors as a function of geolocation and time for a chosen SDO AIA wavelength. The model includes an interface to retrieve raw high-resolution SDO AIA, the model includes horizon computation for a smooth and accurate transition at the terminators. The model is 100% pythonic, featuring parallel execution. We present observations and numerical simulations of the ionosphere-thermosphere system bolstering the importance of the accurate EUV eclipse description. We present use 21 August 2017, and 10 June 2021 solar eclipses as examples to show the effects of realistic EUV flux and transient gradients within the penumbra, and compare it with simulations using symmetric penumbra. We integrated the EUV penumbra in the Global Ionosphere Thermosphere Model (GITM), and show that the difference between EUV and symmetric eclipse amounts to as much as plus-minus 1 TECu.

In this study, field-aligned currents (FACs) obtained from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) dataset have been used to specify high-latitude electric potential in the Global Ionosphere Thermosphere Model (GITM). The advantages and challenges of the FAC-driven simulation are investigated based on a series of numerical experiments and data-model comparisons for the 2013 St Patrick’s Day geomagnetic storm. It is found that the cross-track ion drift measured by the Defense Meteorological Satellite Program (DMSP) satellites can be well reproduced in the FAC-driven simulation when the electron precipitation pattern obtained from Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique is used in GITM. It is also found that properly including the neutral wind dynamo is very important when using FACs to derive the high-latitude electric field. Without the neutral wind dynamo, the cross-polar-cap potential and hemispheric integrated Joule heating could be underestimated by more than 20%. Moreover, the FAC-driven simulation is able to well reproduce the ionospheric response to the geomagnetic storm in the American sector. However, the FAC-driven simulation yields relatively larger data-model discrepancies compared to the AMIE-driven GITM simulation. This may result from inaccurate Joule heating estimations in the FAC-driven simulation caused by the inconsistency between the FAC and electron precipitation patterns. This study indicates that the FAC-driven technique could be a useful tool for studying the coupled ionosphere and thermosphere system provided that the FACs and electron precipitation patterns can be accurately specified.