Radial differential rotation of solar corona using radio emissions

Abstract

ABSTRACT The present work is an effort to investigate possible radial variations in the solar coronal rotation by analysing the solar radio emission data at 15 different frequencies (275–1755 MHz) for the period starting from 1994 July to 1999 May. We used a time series of disc-integrated radio flux recorded daily at these frequencies through radio telescopes situated at the Astronomical Observatory of the Jagellonian University in Cracow. The different frequency radiation originates from different heights in the solar corona. Existing models indicate its origin at the height range from nearly ∼12 000 km (for emission at 275 MHz), below up to ∼2400 km (for emission at 1755 MHz). There are some data gaps in the time series used for the study, so we used statistical analysis using the Lomb–Scargle periodogram (LSP). This method has successfully estimated the periodicity present in time series even with such data gaps. The rotation period estimated through LSP shows variation in the rotation period, which is compared with the earlier reported estimate using auto correlation technique. This study indicates some similarity as well as a contradiction with studies reported earlier. The radial and temporal variation in the solar rotation period are presented and discussed for the whole period analysed.