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Modeling the EUV eclipse penumbra and the impacts of the transient EUV gradients on the Ionosphere-Thermosphere

Presentation #125.41 in the session General Topics: Solar — Poster Session.

Published onOct 20, 2022
Modeling the EUV eclipse penumbra and the impacts of the transient EUV gradients on the Ionosphere-Thermosphere

Solar eclipses are periodic opportunities to study how the ionosphere - thermosphere (I-T) system responds to abated EUV flux. The predictive nature of the eclipses makes them a natural laboratory experiment to validate I-T models through model-data comparison when eclipses traverse regions with dense and high fidelity measurements. The total solar eclipse in August 2017 bolstered the need to consider the sun as a spatially non-uniform source of EUV flux, whereby its solar active regions were projected to the Earth’s atmosphere causing modulations in the plasma production function. The impacts of the solar active regions were observed and discussed in the 1950s-1960s with their impacts observed in the ionosonde observation of the ionospheric E-region.

We will present a model of solar eclipse penumbra, which takes high-resolution images of the solar corona from SDO-AIA and GOES-SUVI instruments, and computes spatially non-uniform eclipse penumbra revealing a pin-hole projection of the solar active regions which cause transient EUV flux gradients in the order of 5-10% per minute. These transient gradients directly overlay the regions of perturbed plasma density measured by Total Electron Content (TEC). We integrate the EUV penumbra into the Global Ionosphere Thermosphere Model (GITM) to evaluate the impacts of the EUV penumbra compared to the use of a simplified spherically symmetric eclipse occultation mask. The model reveals the difference between the simplified penumbra and the EUV penumbra accounts for significant changes in plasma drift, neutral winds, F-region density and height (NmF2 and HmF2), and the TEC. For instance, during the 2017 eclipse, the TEC was under- and over-estimated by 1 TEC unit depending on the geographic position of the observer. Lastly, we will discuss how these EUV transients affect ionospheric electrodynamics, that is conductances, plasma drift, and neutral wind, which then impact the whole magnetosphere-ionosphere coupling.

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