Chinese sunspot drawings and their digitization − (IV) differential rotation profile determined from hand-drawing records

It is necessary to better understand the dynamic process of solar differential rotation. Here the hand-drawing sunspot group records from 1958 to 2015 of Yunnan Observatories (YNAO) are used to study the solar rotation profile. Firstly, the rotation profile in each solar cycle 19-23 is calculated. Secondly, the rotation parameters (equatorial rotation velocity A and differential gradient B) of YNAO are compared with the well-known earlier results. Finally, the rotation parameters in the northern and southern hemispheres during each solar cycle 19-23 are summarized. The main conclusions we reached are as follows: (1) The average difference of the equatorial rotation velocity and differential gradient, between YNAO sunspot and other sunspot datasets, are 0.09 and 0.4, respectively. (2) The magnitudes of the gradient B in the northern hemisphere are larger than that in the southern hemisphere at even-number cycles, and it will approximately reverse at odd-number cycles.