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Description
The geomagnetic storm of 10 − 12 May 2024 was the first extreme storm of the solar cycle 25 and the largest storm in more than 20 years. During this super-intense geomagnetic disturbance, the auroral oval expanded to sub-auroral regions with lower geomagnetic latitudes than those of the observatories standardly used to calculate the indices AU, AL, and AE. The relationship between the main Space Weather processes of the respective period (solar storms, CMEs and high-speed solar wind) and Space Weather effects/impacts is briefly recalled in this contribution. Our study proposes an auroral-oval activity quantification in terms of an adjusted AEa index during this particularly intense magnetic storm, taking into account the fact that the auroral oval is not a stationary feature. We also compared the standard AE index and our adjusted index with the modified AEm index of other authors who proposed a correction to the AE index through an empirical model based on solar wind parameters. The AEa index might underestimate the auroral activity due to the saturation of the Kp index, which we used to determine the position of the auroral oval boundary. Another auroral activity index SME showed a similar profile during the disturbed period as AEa but reached higher values. Further research will have to focus on dealing with the undesirable consequences of Kp index saturation on our method. Boundaries of the auroral oval can also be described using an open-ended index such as Hp30 or Hp60, which should hopefully help to improve our method.
