Statistical analysis of the sunspot area and magnetic flux variations in 1996–2005 extracted from the Solar Feature Catalogue

Abstract

This research presents some statistical properties of sunspots and their magnetic fields extracted in from May 1996 to May 2005 from the SOHO/MDI full disk whitelight images and magnetograms for the searchable Solar Feature Catalogue (SFC) using the automated pattern recognition techniques. A comparison of the total sunspot areas on a given day from the SFC with the daily sunspot areas available from US AF SOON data for 2000–2004 reveal a very good correlation of the datasets with the correlation coefficient of ∼93%. The total sunspot areas in the Northern and Southern hemispheres measured from a single solar image and their cumulative areas during the whole cycle are shown to have a strong North-South asymmetry with the Northern hemisphere prevailing around and after the maximum while the Southern one Schatten taking over towards the coming solar minimum. The similar N-S asymmetry is observed in a total and resulting, or excess, magnetic fluxes. The former is found to follow closely the N-S asymmetry in the sunspot areas while the latter shows a very significant flux separation in the opposite hemispheres. The excess flux is negative in the Southern hemisphere and positive in the Northern one during a long period from 1997 until 2004. During the solar minimum in 1996, the signs of total excess fluxes in the hemispheres are changed to the opposite and a similar change appears in 2003–2004 towards the approaching solar minimum. Since the magnetic field in sunspots is those of the leading polarity, so the excess magnetic flux evolution is believed to show a change of the magnetic field leading polarity during the solar cycle minima, while the asymmetry of the total magnetic flux, possibly, reflects the asymmetry of a poloidal magnetic field, as it is predicted by the oscillatory dynamo models.