Speaker
Description
Due to geomagnetic dipole tilt, the solar zenith angles and the resultant ionospheric conductivities at the same geomagnetic (GM) latitude and local time are highest in the tilt direction, which are the North American sector in the northern hemisphere and the Australian-New Zealand sector in the southern hemisphere. As a result, the geomagnetic disturbances at observatories in the tilt direction should be higher than those at others during the same level of ionospheric and magnetospheric activity. This unevenness affects the AE and Kp stations used to calculate the geomagnetic Kp and AE indices. We consider this effect for very high values of AU > 1200 nT and Kp ≥ 9-. Past statistics shows that occurrence frequencies of the very high AU> 1200 nT and Kp≥9- depend on UT, depending on the geographic latitudes of postnoon stations. Since G-scale is defined by Kp, the result indicates that some G4 geomagnetic storms occurring at 09-15 UT may be as severe as G5 storms, and that the May 2024 space weather event is the most severe one occurring at 09-15 UT since 1978.
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