Dark dots on the photosphere and counting of the sunspots index

TL;DR

This study analyzes small dark regions on the Sun's photosphere observed via satellite, investigating their properties, magnetic characteristics, and potential impact on sunspot counting, revealing many are non-magnetic and may affect sunspot indices.

Contribution

It provides a detailed analysis of dark points on the Sun, their magnetic properties, and implications for sunspot index calculations, using high-resolution satellite data from 2010-2020.

Findings

Most dark points under 5 mhm have weak magnetic fields (<30 G).

Dark points are often non-magnetic and can be mistaken for pores.

The presence of these structures influences sunspot index assessments.

Abstract

On modern satellite observations of the Sun in the continuum with high spatial resolution, as well as on high-quality ground observations, a large number of small dark areas can be observed. These regions have no penumbra, have a contrast of up to 20% and are similar to solar pores. The characteristic area of such structures is $0.3\div5\ \mu$hm or $0.5\div5$ Mm. The number of such points in one image can be several hundred. The nature of such formations remains unclear. We have performed the selection of dark regions with a contrast of at least 3% of the level of the quiet Sun on the SDO/HMI observational data in the continuum for 2010-2020. We have studied the properties of "dark points, including the change with the cycle of activity, area distribution and contrast. We also compared such structures with the intensity of the magnetic field. We found that the number of dark dots with an area of less than 5 mhm, in which the magnetic field is not significant and is less than |B|<30 G, is from 60 to 80% of the total number of structures of this size. This means that these objects are not associated with magnetic activity. The existence of such structures can significantly affect the calculations of the sunspot index, since they can be mistaken as pores.