An analysis of the solar differential rotation from the Kanzelhoehe sunspot drawings

We present here the results of the behaviour of the solar differential rotation during solar cycles no. 20 and no. 22, derived from Kanzelhohe sunspot drawings (Kanzel- hohe Observatory for Solar and Environmental Research, University of Graz, Austria). The positions of sunspot groups were determined using a special software Sungrabber. Sunspot groups were identified with the help of the Greenwich Photoheliographic Results (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering solar cycles no. 20 and no. 22, respectively. In order to calculate the sidereal angular rotation rate ! and subsequently solar rotation parameters A and B we used two procedures: a) daily motion of sunspot groups and b) linear least-square fit from the function CMD(t) for each tracer, where CMD denotes the Central Meridian Distance. The sample was limited to ±58 ◦ in CMD in order to avoid solar limb effects. We mainly investigated velocity patterns depending on the solar cycle phase and latitude.