Time Distributions of Large and Small Sunspot Groups Over Four Solar Cycles

TL;DR

This study analyzes the time variation of small and large sunspot groups over four solar cycles, revealing differences in their peak timings and correlations with solar activity indicators, which enhances understanding of solar activity and its impact on Earth.

Contribution

It provides a detailed comparison of the temporal behavior of small and large sunspot groups across multiple solar cycles, highlighting their different relationships with solar activity measures.

Findings

Large sunspot groups peak mid-cycle (phase 0.45-0.5).

Small sunspot groups peak earlier (phase 0.29-0.35).

Large sunspot groups correlate better with solar radio flux and CME speed.

Abstract

Here we analyze solar activity by focusing on time variations of the number of sunspot groups (SGs) as a function of their modified Zurich class. We analyzed data for solar cycles 2023 by using Rome (cycles 2021) and Learmonth Solar Observatory (cycles 2223) SG numbers. All SGs recorded during these time intervals were separated into two groups. The first group includes small SGs (A, B, C, H, and J classes by Zurich classification) and the second group consists of large SGs (D, E, F, and G classes). We then calculated small and large SG numbers from their daily mean numbers as observed on the solar disk during a given month. We report that the time variations of small and large SG numbers are asymmetric except for the solar cycle 22. In general large SG numbers appear to reach their maximum in the middle of the solar cycle (phase 0.450.5), while the international sunspot numbers and the small SG numbers generally peak much earlier (solar cycle phase 0.290.35). Moreover, the 10.7 cm solar radio flux, the facular area, and the maximum CME speed show better agreement with the large SG numbers than they do with the small SG numbers. Our results suggest that the large SG numbers are more likely to shed light on solar activity and its geophysical implications. Our findings may also influence our understanding of long term variations of the total solar irradiance, which is thought to be an important factor in the Sun - Earth climate relationship.