Clarifying Physical Properties of Magnetic Fields in Sunspots

TL;DR

This study investigates the magnetic field properties of sunspots, revealing consistent radial magnetic components, slight growth in mean magnetic field with sunspot size, and a nonlinear relation between total magnetic flux and sunspot area.

Contribution

It provides new quantitative parametrizations of magnetic flux relations and clarifies the magnetic flux contribution of sunspots to the solar magnetic field.

Findings

Radial magnetic-field component at sunspot boundary is about 550 Mx/cm², independent of sunspot size.

Mean magnetic field in sunspots increases slightly with size, reaching 900-2000 Mx/cm².

Sunspot magnetic flux contributes less than 20% to the total solar magnetic flux.

Abstract

We demonstrate that the radial magnetic-field component at the outer boundary of the sunspot penumbra is about 550 Mx cm$^{-2}$ independent of the sunspot area and the maximum magnetic field in the umbra. The mean magnetic-field intensity in sunspots grows slightly as the sunspot area increases up to 500 -- 1000 millionth of visual hemisphere (m.v.h.) and may reach about 900 -- 2000 Mx cm$^{-2}$. The total magnetic flux weakly depends on the maximum field strength in a sunspot and is determined by the spottedness, i.e. the sunspot number and the total sunspot area; however, the relation between the total flux and the sunspot area is substantially nonlinear. We suggest an explicit parametrization for this relation. The contribution of the magnetic flux associated with sunspots to the total magnetic flux is small, not achieving more than 20% even at the maximum of the solar activity.