Effect of a Flare Late Phase on the Earth’s Ionosphere

One variant of coronal loop reconnection following the impulsive phase of a flare results in warm coronal emissions (such as Fe XV 28.4 nm and Fe XVI 33.5 nm) exhibiting a second, large emission peak that can lag the primary flare by hours. This secondary peak is known as an extreme-ultraviolet late phase (ELP).

The effect of the late phase on Earth's ionosphere was discovered only in 2024. The associated press release ranked in the top 0.1% of all research outputs tracked by Altmetric, reflecting exceptional interest beyond the academic community.

Below, you can read how our research evolved: from an initial case study to a large-scale statistical analysis.

Time-wavelength map of background-subtracted solar irradiance across EUV emission lines, with the GOES 0.1-0.8 nm X-ray flux overplotted. The hot lines peak with the X-ray flux; Fe XV 28.4 nm and Fe XVI 33.5 nm brighten again well afterwards.
Figure 1. Relative irradiance in 31 spectral lines measured by SDO/EVE during the X2.9 flare on 3 November 2011. The vertical dashed line indicates the time of maximum X-ray flux (main phase), while the vertical dotted line indicates the time of maximum Fe XVI 33.5 nm flux (late phase).
Two panels. Left: relative TEC against a smooth quiet-time reference curve. Right: the difference between them, with one peak during the main phase and a second, smaller one during the late phase.
Figure 2. Left panel: relative TEC values (black) and the subtracted trend (red) obtained at GPS station during the main phase of the X2.9 flare on 3 November 2011. Right panel: corresponding ΔTEC variations during the main and late phases of the flare.

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