  The present study is an attempt to investigate the long term variations in
coronal rotation by analyzing 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 to 29.5 sidereal days (mean
sidereal rotation period is 24.3 days). This variation in the coronal rotation
period shows evidence of two components in the variation; (1) 22-years
component which may be related to the solar magnetic field reversal cycle or
Hale's cycle, and (3) a component which is irregular in nature, but dominates
over the other components. The crosscorrelation analysis between the annual
average sunspots number and the coronal rotation period also shows evidence of
its correlation with the 22-years Hale's cycle. The 22-years component is found
to be almost in phase with the corresponding periodicities in the variation of
the sunspots number.
