Temporal relations between magnetic bright points and the solar sunspot cycle

Abstract

The Sun shows a global magnetic field cycle traditionally best visible in the photosphere as a changing sunspot cycle featuring roughly an 11 year period. In addition we know that our host star also harbours small-scale magnetic fields often seen as strong concentrations of magnetic flux reaching kG field strengths. These features are situated in inter-granular lanes where they show up bright as so-called magnetic bright points (MBPs). In this short paper we wish to analyse a homogenous nearly 10 year long synoptic Hinode image data set recorded from November 2006 up to February 2016 in the G-band to inspect the relationship between the number of MBPs at the solar disc centre and the relative sunspot number. Our findings suggest that indeed the number of MBPs at the solar disc centre is correlated to the relative sunspot number, but with the particular feature of showing two different temporal shifts between the decreasing phase of cycle 23 including the minimum and the increasing phase of cycle 24 including the maximum. While the former is shifted by about 22 months the later is only shifted by less than 12 months. Moreover, we introduce and discuss an analytical model to predict the number of MBPs at the solar disc centre purely depending on the evolution of the relative sunspot number as well as the temporal change of the relative sunspot number and two background parameters describing a possibly acting surface dynamo as well as the strength of the magnetic field diffusion. Finally, we are able to confirm the plausibility of the temporal shifts by a simplistic random walk model. The main conclusion to be drawn from this work is that the injection of magnetic flux, coming from active regions as represented by sunspots, happens on faster time scales than the removal of small-scale magnetic flux elements later on.

arXiv comment12 pages, 12 figures, 3 tables, proceeding/paper of the 10-years anniversary Hinode conference hosted in Nagoya/Japan

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