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

II. Dynamics of the differential rotation of the Sun

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: 15 November 2001
Accepted: 15 April 2002

Abstract

An analysis of solar rotation as a function of heliographic latitude and time is made using daily radio maps of the Sun at the wavelength of 1.76 cm. Variations of the velocity as a function of the latitude during the period 1992–2001 have been studied. The mean synodical rotation rate of the intensity features is best fit by where θ is the latitude. We have found alternating bands of faster and slower rotation. They travel from higher latitudes towards the equator during the current solar cycle.
Radio observations with high accuracy and reliability thus confirm the reality of torsional oscillations in the higher levels of the solar atmosphere.