Abstract:
Differential rotation is one of the basic characteristics of the Sun, and it plays an important role in generating the
magnetic fields and its activities. We investigated rotation rate using chromospheric features such as plages,
enhanced network (EN), active network (AN), and quiet network (QN) separately (for the first time). The digitized
Ca-K images from Kodaikanal Observatory for 1907–1996 are used to study rotation over 0°–80° latitudes at an
interval of 10°. We find that plages and all types of networks exhibit the differential rotation of the chromosphere.
Furthermore, the rotation rate shows a decreasing pattern as one move from the equator to the higher polar latitudes
for all the features used in the study. At the equator the rotation rate (rotation period) is obtained to be ∼13.98°
day−1 (25.74 days), ∼13.91° day−1 (25.88 days), ∼13.99° day−1 (25.74 days), and ∼14.11° day−1 (25.51 days)
for plage, EN, AN, and QN areas, respectively. By analyzing how the area of chromospheric features varies over
time, we can effectively map the Sun’s rotation rate at all latitudes, including the polar regions. Interestingly, both
plages and small-scale networks exhibit a similar differential rotation rate. This suggests these features likely
rooted at the same layer below the visible surface of the Sun. Therefore, the long-term Ca-K data is very useful for
studying the solar rotation rate at all latitudes including the polar regions.
