Long-term variations of the coronal rotation and solar activity

Abstract

Recently, Chandra and Vats have obtained the yearly period length of the solar coronal rotation cycle by analysing the daily adjusted solar radio flux at the 10.7-cm wavelength for the years 1947-2009. In this paper, we use the time series (series I) of the yearly period length to investigate the long-term variation of the rotation of radio emission corona, and we find a weak decreasing trend in the time series. We use the empirical mode decomposition to decompose both the yearly mean value (series II) of the solar radio flux at the 10.7-cm wavelength and series I into different periodical components. There is a secular trend for each of the two series, and we find a negative correlation in the two trends. The decomposed 11-yr-cycle components of the two series show different and complicated periods and there is a phase relation between them. We investigate the cycle-related variation of the coronal rotation length, and we find that there is no Schwable cycle of statistical significance for the long-term variation of the rotation cycle length. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.