Speaker
Description
X-ray and EUV solar flare emission cause increases in the Earth's dayside ionospheric electron density. While the response of the lower ionosphere to X-rays is well studied, the delay between EUV flare emission and the response of the ionospheric F-region had not been investigated. Here we calculated the delays between incident He II 304 Å emission and the TEC response for 10 powerful solar flares, all of which exhibit delays under 1 minute. We assessed these delays in relation to multiple solar and geophysical factors, and found a strong negative correlation between delay and He II flux change and a moderate negative correlation with rate of increase in He II flux. Additionally, flare magnitude and the X-ray-to-He II flux ratio at peak He II emission showed strong negative correlations with delay. We also identified longer delays for flares occurring closer to the summer solstice. These results may have applications in upper-ionospheric recombination rate calculations, atmospheric modelling, and other solar-terrestrial studies. We highlight the importance of incident EUV and X-ray flux parameters on the response time of the ionospheric electron content, and these findings may also have implications for mitigating disruptions in communication and navigation systems.
