Extreme Value Analysis of Solar Green‐Line Corona During the Time Interval 1939–2025

Predicting the probability of extreme solar events is critical to understanding how to mitigate risks associated with space weather disasters, as their occurrence can pose a threat to life and infrastructure on Earth or in near‐Earth orbit. In the present study, extreme value theory is applied to the daily modified coronal index (MCI) for the period 1 January 1939–30 April 2025 to assess the characteristics of the extreme solar activity events over a long time scale and the likelihood of their occurrence in the future. The shape parameters of the generalized extreme value distribution estimated using the block maxima approach and those of the generalized Pareto distribution estimated using the peaks‐over‐threshold approach are both negative within the 95% confidence interval, indicating that the extreme values of the daily MCI have an upper limit. The return level obtained from the peaks‐over‐threshold approach suggests that the 100‐year return level (200‐year and 500‐year return level) is below (close to or above) the observed maximum value of the daily MCI (9.165), implying that it is shown to be a 1‐in‐200 year event. These results indicate that solar green‐line corona has reached its upper limit during the past eight solar cycles and the likelihood of observing values significantly higher than this maximum value in the near future is low. These findings provide clues for avoiding or mitigating the problems that extreme solar activity may pose to human society.