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Table 1

Parameters and activity levels describing MOD and SEV level activity for shortwave fadeout (SWF), auroral absorption (AA), polar cap absorption (PCA), and post-storm maximum usable frequency depression (PSD) based on ICAO regulations (ICAO, 2019).

Sub-effect Parameter MOD SEV
SWF Solar X-ray flux (0.1–0.8 nm wavelength) (Wm−2) 1 × 10−4 (X1) 1 × 10−3 (X10)
AA Kp index 8 9
PCA Absorption at 30 MHz (dB) 2 5
PSD MUF* 30% 50%

Compared to a 30-day running median of the critical frequency of the foF2.

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