Variability of the solar coronal rotation

Abstract

Helioseismology measurements have begun to provide a picture of Suns angular velocity as a function of both depth and latitude. The rate of improvement of our knowledge has been fast and is likely to be more so for the near future. This has the potential of providing a nearly complete picture of the solar rotation throughout solar interior. The rotation of the solar photosphere is usually measured by tracking tracers e.g., sunspots, faculae, low-level magnetic features, Little is known about the solar coronal rotation etc. We recently attempted a fractal analysis of radio emission from the solar corona and found that the time series of radio emission at several frequencies can be easily be used for determining the rotation of the solar corona. The study reveals several interesting features about the rotation of the solar corona. The solar corona rotates faster than the photosphere. It is not possible to investigate latitudinal variations of the solar coronal rotation by this method, however, it is certainly possible to investigate temporal changes of this rotation. It is found that the coronal rotation period varies during different phases of the solar cycle. Here, the results of an auto correlation analysis for the solar cycles 21 and 22 will be presented and compared with those obtained by other methods.