Why the ionosphere has an eclipse hangover?

What is it about?

This is an effort to understand why the Earth's ionosphere—a charged layer of the atmosphere crucial for radio and GPS signals—takes so long to recover its strength after a solar eclipse, long after the sun has reappeared. To do this, we used a powerful radar and a network of GPS receivers to take a detailed look at the atmosphere over the Arctic during a solar eclipse. This allowed us to see how the eclipse affected different layers of the ionosphere, from bottom to top, simultaneously. We found that while the lower part of the ionosphere recovers quickly, the upper part stays depleted for hours. This is because the eclipse creates a pressure imbalance, causing charged particles to drain downwards from the top, and it also cools and thins out the neutral gas, which is needed to create new particles. It's a double whammy that slows everything down. The solar eclipse at high latitudes caused the ionosphere to take hours to recover. This was because the lower ionosphere recovered quickly, but the upper layer took longer. This ongoing loss of material at the top of the atmosphere, caused by differences in pressure and diffusion, led to a slow recovery of the total electron content (TEC), which is important for GPS signals. What's more, a drop in the amount of neutral density in the air, which was measured by GRACE-FO satellite, probably made things even worse by reducing the amount of material available for ionisation. Key Points: * Ionospheric impacts of high latitude solar eclipse on 10 June 2021 are studied by incoherent scatter radars and GNSS measurements. * Altitude-dependent responses are found in electron density but not in electron temperature. * A delayed and persistent depletion in the topside ionospheric density causes prolonged recovery of total electron content after eclipse.

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Photo by Austin Schmid on Unsplash

Photo by Austin Schmid on Unsplash

Why is it important?

This work is unique because it provides a rare, simultaneous, and high-resolution view of both the neutral atmosphere and the ionised plasma during a high-latitude eclipse, connecting the dots between them. Many studies have already documented the total electron content (TEC) drop. But this research uniquely pinpoints the altitude-dependent mechanics causing the prolonged recovery. It specifically identifies the ongoing depletion of the topside ionosphere and its link to plasma diffusion and a simultaneous reduction in neutral density. This multi-instrument approach using EISCAT radars, GNSS, and GRACE-FO data offers a more complete physical explanation than previous studies. This is important because more and more of our society depends on accurate GPS technology, and it is crucial that we understand these disruptive events.

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