Periodicities in the coronal rotation and sunspot numbers

Abstract

This study is an attempt to investigate the long-term variations in coronal rotation by analysing the time-series of the solar radio emission data at 2.8 GHz frequency for the period 1947-2009. Here, daily adjusted radio flux (known as Penticton flux) data are used. The autocorrelation analysis shows that the rotation period varies between 19.0-29.5 sidereal days (mean sidereal rotation period is 24.3 d). This variation in the coronal rotation period shows evidence of two components in the variation: (1) 22-yr component which may be related to the solar magnetic field reversal cycle or Hale's cycle; and (2) a component which is irregular in nature, but dominates over the other components. The cross-correlation analysis between the annual average sunspot number and the coronal rotation period also shows evidence of its correlation with 22-yr Hale's cycle. The 22-yr component is found to be almost in phase with the corresponding periodicities in the variation of the sunspot number. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.