Abstract
Context. The relationship between bipolar magnetic regions (BMRs) and their sunspots is an important property of the solar magnetic field, but it is not well constrained. One consequence is that it is a challenge for surface flux transport models (SFTMs) based on sunspot observations to determine the details of BMR emergence, which they require as input, from such data. Aims. We aimed to establish the relationship between the amount of magnetic flux in newly emerged BMRs and the area of the enclosed sunspots, and examine the results of its application to an established SFTM. Methods. Earlier attempts to constrain BMR magnetic flux were hindered by the fact that there is no extensive and reliable record of the magnetic and physical properties of newly emerged BMRs currently available. We made use of the empirical model of the relationship between the disc-integrated facular and network magnetic flux and the total surface coverage by sunspots reported in a recent study. The structure of the model is such that it enabled us to establish, from these disc-integrated quantities, an empirical relationship between the magnetic flux and sunspot area of individual newly emerged BMRs, circumventing the lack of any proper BMR database. Results. Applying the constraint on BMR magnetic flux derived here to an established SFTM retained its key features, in particular its ability to replicate various independent datasets and the correlation between the model output polar field at the end of each cycle and the observed strength of the following cycle. The SFTM output indicates that facular and network magnetic flux rises with increasing sunspot magnetic flux at a slowing rate such that it appears to gradually saturate. This is analogous to what earlier studies comparing disc-integrated quantities sensitive to the amount of faculae and network present to sunspot indices had reported. The activity dependence of the ratio of facular and network flux to sunspot flux is consistent with the findings of recent studies: although the Sun is faculae-dominated (such that its brightness is mostly positively correlated with activity), it is only marginally so as facular and network brightening and sunspot darkening appear to be closely balanced.
Highlights
The global solar dynamo produces the cyclic emergence of bipolar magnetic regions (BMRs) on the solar surface which underlies the 11-year activity cycle (Charbonneau 2020)
How the larger BMRs relate to the sunspots they enclose and how ephemeral regions (ERs) emergence relates to the number of sunspots present are of interest as they connect directly to how solar magnetism and activity relate to sunspot prevalence, with implications for the study of a wide range of solar phenomena
YSK argued that it is unlikely that the amount of facular and network magnetic flux associated with a sunspot-bearing BMR conforms to a linear relationship with the area of the enclosed sunspots
Summary
The global solar dynamo produces the cyclic emergence of bipolar magnetic regions (BMRs) on the solar surface which underlies the 11-year activity cycle (Charbonneau 2020). We derive an empirical relationship between the amount of magnetic flux in each newly emerged bipolar magnetic region or BMR, ΦBMR, and the area of the enclosed sunspots, ABMR,S For this purpose we employ the empirical model of the relationship between the disc-integrated facular and network magnetic flux, ΣΦFN, and the total surface coverage by sunspots, ΣAS, recently reported by YSK (Yeo et al 2020). YSK argued that it is unlikely that the amount of facular and network magnetic flux associated with a sunspot-bearing BMR conforms to a linear relationship with the area of the enclosed sunspots They introduced the fit parameter h1, such that the variation in ΣΦFN is given by (ΣAS)h1 ⊗ H instead. Less than 10% of the data points in the daily ΣΦFN composite by Yeo et al (2014b) lie in this period
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