Differential coronal rotation and solar activity

Satish Chandra1* and Hari Om Vats2†
1Department of Physics, PPN College, Kanpur 208 001, India
2Physical Research Laboratory, Ahmedabad 380 009, India

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We investigated the latitudinal variation in the coronal rotation by using observations taken with Nobeyama Radioheliograph (NoRH) at 17 GHz. The time series bins are formed on different latitude regions of the solar full disc (SFD) radio image, which extend up to ±60˚ in both the hemispheres. The sidereal rotation rate as a function of latitude for each year during 1999-2005 are obtained. The analysis reveals that the equatorial rotation rate of the corona is comparable to the photosphere and the chromosphere. However, at higher latitudes, the corona rotates less differently than the photosphere and the chromosphere. The differential rotation obtained at the height of these emissions is quite variable throughout the period of study. The equatorial rotation period and latitude dependent differential rate seem to vary almost systematically with sunspot numbers. This indicates its dependence on the phases of the solar activity cycle.

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Keywords : Sun: corona – Sun: radio radiation – Sun: rotation