Spot cycle reconstruction: an empirical tool^⋆

Application to the sunspot cycle

¹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
e-mail: asantos@astro.up.pt
² Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
³ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
⁴ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Received: 7 November 2014
Accepted: 4 June 2015

Abstract

Context. The increasing interest in understanding stellar magnetic activity cycles is a strong motivation for the development of parameterized starspot models which can be constrained observationally.

Aims. In this work we develop an empirical tool for the stochastic reconstruction of sunspot cycles, using the average solar properties as a reference.

Methods. The synthetic sunspot cycle is compared with the sunspot data extracted from the National Geophysical Data Center, in particular using the Kolmogorov-Smirnov test. This tool yields synthetic spot group records, including date, area, latitude, longitude, rotation rate of the solar surface at the group’s latitude, and an identification number.

Results. Comparison of the stochastic reconstructions with the daily sunspot records confirms that our empirical model is able to successfully reproduce the main properties of the solar sunspot cycle. As a by-product of this work, we show that the Gnevyshev-Waldmeier rule, which describes the spots’ area-lifetime relation, is not adequate for small groups and we propose an effective correction to that relation which leads to a closer agreement between the synthetic sunspot cycle and the observations.