SOLARNET Conference: The Many Scales of the Magnetic Sun

Differential rotation is a key aspect of the solar dynamo model and is well-established in the Sun's interior and photosphere. However, our understanding of the chromosphere and upper atmosphere's differential rotation is limited and has yielded contradictory results in previous studies. To address this, we utilized a century-long dataset of Ca II K images (1907-2007) from the Kodaikanal Solar Observatory (KoSO) to investigate the chromosphere's rotation profile during different solar cycles. By employing the image correlation analysis on sets of consecutive day images, we found that the chromosphere rotates 1.52% faster than the photosphere but with less differential rotation compared to the photosphere values. To validate our method and results, we applied the same technique to MDI white light data and other Ca II K data sources (Meudon and PSPT/Rome) and obtained consistent results. Moreover, we examined the solar cycle dependence of differential rotation parameters and investigated the north-south asymmetry of the solar rotation profile.