The Growth and Decay of Individual Sunspots and Pores

TL;DR

This study analyzes the growth and decay rates of sunspots and pores using SDO/HMI data from 2010 to 2025, revealing non-monotonic dependencies on area and differences based on polarity.

Contribution

It provides detailed quantitative relationships for sunspot and pore evolution, including area-dependent growth and decay rates, and polarity-based differences, based on extensive observational data.

Findings

Growth and decay rates depend non-monotonically on sunspot area.

Small sunspots grow and decay faster with increasing area.

Pores show linear growth and decay rates related to their area.

Abstract

An analysis of the photometric growth and decay rates of sunspots and pores was carried out. According to the \textit{Solar Dynamics Observatory/Helioseismic and Magnetic Imager} (SDO/HMI) data for the period 05.2010-03-2025, $\approx 3.5\cdot 10^{\rm 5}$ sunspots and pores were detected and their evolution tracked. The growth and decay rates of sunspots depend non-monotonically on the area. For small-area sunspots $S \lesssim 50$ $\mu$sh, a rapid increase in velocity is observed with increasing the area for the growth stage $dS^{\rm gr}_{\rm sp}\approx 0.2 \cdot S^{\rm 1.35}$ and for the decay stage $dS^{\rm dc}_{\rm sp}\approx 0.28 \cdot S^{\rm 1.26} $ $\mu$sh/day. For sunspots $S\gtrsim 50$ $\mu$sh, the growth rate depends weakly on the area: $dS^{\rm gr}_{\rm sp}\approx 11.9 \cdot S^{\rm 0.32}$ $\mu$sh/day. For the decay stage of sunspots with an area of $S\approx 50\,-\,150$ $\mu$sh, the decay rate also depends weakly on the area and can be approximated as $dS^{\rm dc}_{\rm sp}\approx 11 \cdot S^{\rm 0.15} $. For sunspot areas $S\gtrsim 150$ $\mu$sh, the decay rate accelerates with increasing area: $dS^{\rm dc}_{\rm sp}\approx 0.14 \cdot S^{\rm 0.96} $ $\mu$sh/day. For solar pores, the growth and decay rates of solar pores are linearly related to the area. The growth and decay rates for the spots of the leading and trailing polarities are determined. In the range of spot areas $S\approx 100\,-\,200$ $\mu$sh, the growth and decay rates of sunspots of trailing polarity are higher than those of sunspots of leading polarity.