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Keywords:

  • methods: data analysis;
  • Sun: activity;
  • Sun: corona;
  • Sun: rotation

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.