A study of the development of global solar activity in the 23rd solar cycle based on radio observations with the Nobeyama radio heliograph

I. Latitude distribution of the active and dark regions

¹ Pulkovo Astronomical Observatory, 196140 Saint Petersburg, Russia
² Tuorla Observatory, 21500 Piikkiö, Finland
³ Nobeyama Radio Observatory, Minamisaku, Nagano 384-13, Japan

Corresponding author: A. Riehokainen, alrieho@astro.utu.fi

Received: 11 October 2001
Accepted: 15 April 2002

Abstract

Daily radio maps of the Sun at the wavelength of 1.76 cm were used to analyze the parameters of solar activity at all heliographic latitudes for the period 1992–2001. As a criterion of the level of solar activity, we analyzed the area/number of regions with an excess of brightness above a certain fixed level as well as regions with brightness below a certain level. The distribution of such “bright” and “dark” regions with heliographic latitude as function of time was found. Special attention was paid to the high latitude polar regions where the ways of analyzing solar activity are rather limited and have no generally accepted methods. The results are compared with some other indices of high latitude solar activity, such as polar faculae and magnetic field measurements. They appear to be in general agreement with the radio observations. The advantage of using radio observations is a more homogeneous database and a stable method of analysis.