Geomagnetic storms and sudden ionospheric disturbances (SID)

Besides flares and proton outbursts, the cavity is also affected by geomagnetic storms and sudden ionospheric disturbances (SID). SIDs are rapid changes in the ionization of the D-region caused primarily by a solar X-ray flash, manifesting themselves practically immediately on the day side; geomagnetic storms are associated with disturbances of the magnetosphere and ionosphere during increased solar and particle activity Satori 2016.

Both groups of phenomena change the state of the upper boundary of the cavity, and thus the SR parameters — especially the frequencies of the modes and the damping. In time, SIDs coincide with the course of the corresponding flare, whereas geomagnetic storms can act longer and over a broader range of geographic latitudes.

These disturbances should therefore be identified during the analysis of SR records using independent space-weather indices, so that they are not mistaken for changes in the lightning activity itself.