Study of Solar Coronal Rotation using Nobeyama Radio Heliograph (NoRH) at 17 GHz

The solar activity cycle is closely linked to the solar rotation, making rotation one of the Sun’s most fundamental properties. The Sun does not rotate uniformly; its rotation rate varies with both altitude and latitude. However, the available information on solar rotation remains insufficient for fully predicting solar activity and, consequently, space weather. Solar rotation can be studied using several approaches, including tracer tracking on the solar surface, spectral analysis and flux modulation. In this study, solar rotation is determined through flux modulation, while Lomb–Scargle periodogram (LSP) is employed to identify periodicities in the data. In the flux modulation method, radio features crossing the solar disc are monitored, and statistical analysis of daily radioheliograph images (spanning 1992–2020) provides rotation periods as a function of latitude. Periodic components within these time series are extracted using statistical techniques such as LSP. The analysis is conducted on latitude bins, each representing equally spaced regions, seperated by 5°, across the solar full-disc (SFD) images from the Nobeyama Radioheliograph (NoRH) at 17 GHz, covering latitudes from 45°S to 45°N. A least-squares polynomial fit is applied to the rotational profiles of the northern and southern hemispheres. The resulting differential coefficients are found to vary with the sunspot cycle. The findings reveal both rigid and differential rotation across different epochs, specifically from the declining phase of SC 22 through the conclusion of SC 24.