Abstract
In May 2024, a series of coronal mass ejections (CMEs) resulted in the
first ’severe’ (G4-level) geomagnetic storm watch in nearly 20 years.
This event evolved into a significant space weather event, including an
’extreme’ (G5) geomagnetic storm, moderate (S2) solar radiation storm,
and strong (R3) radio blackout. The widespread visibility of auroras at
unusually low latitudes attracted global media attention. Using extreme
value theory (EVT), this study estimates the return periods for the May
2024 storm based on several geomagnetic indices. The results indicate
that while the storm’s magnitude was a 1-in-12.5-year event, its
duration was a 1-in-41-year event. This discrepancy highlights the
storm’s unusual longevity compared to its intensity. Updated EVT
analyses incorporating recent data refine these return period estimates,
providing critical insights into the frequency of such extreme space
weather events.