Solar Cycle 25 Dynamics from Observational and Statistical Parameters: Characterization of the Maximum Phase and Rotational Behaviour

TL;DR

This paper analyzes Solar Cycle 25's maximum activity phase using multiple observational parameters, identifying August 2024 to January 2025 as the peak period with heightened eruptive activity and magnetic field reversal.

Contribution

It introduces a percentile-based classification of F10.7 flux to precisely define the cycle's maximum activity interval and combines observational data with solar rotation analysis.

Findings

Maximum activity period: August 2024 to January 2025.

Over 190 M-class and 19 X-class flares occurred during this period.

Solar rotation periods vary between approximately 21.77 to 22.78 days.

Abstract

We present a comprehensive analysis of Solar Cycle 25 aimed at precisely constraining the interval of its activity maximum using multiple observational parameters: sunspot number (SSN), Wolf number, the 10.7 cm solar radio flux (F10.7), the occurrence rate and speed of coronal mass ejections (CMEs), the statistics of X-ray flares, and the reversal of the global magnetic field. A percentile-based classification of the adjusted F10.7 flux (EPH scale) is introduced, which allows us to identify the maximum-activity interval as August 2024 to January 2025. This period coincides with the reversal of the solar polar fields and is characterized by enhanced eruptive activity, including more than 190 M-class and 19 X-class flares (including an X6.3 flare on 10 December 2024) and multiple CMEs with speeds exceeding 2000 km/s. In the second part of the study we investigate solar rotation during this cycle using an independent observing campaign conducted in April 2025 in San Jose, Costa Rica, with privately owned telescopes in white light and in the H alpha line. Photometric techniques and active-region tracking yield mean synodic angular velocities of 12.8 +/- 2.8 deg/day in the northern hemisphere and 13.38 +/- 0.54 deg/day in the southern hemisphere, corresponding to sidereal periods of 22.78 and 21.77 days, respectively. Complementary SWPC-NOAA sunspot-region data provide synodic periods between 21.19 and 25.74 days, consistent with classical differential-rotation measurements. Linear velocities derived from SDO images span from about 872 km/h to more than 7400 km/h, depending on latitude and date.