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We determined the differential rotation (DR) parameters $A$ and $B$(corresponding to the equatorial rotation velocity and the gradient of thesolar DR) by tracing sunspot groups in sunspot drawings of the Kanzelh\"oheObservatory for Solar and Environmental Research (KSO; 1964-2008, for solarcycles (SC) 20-23) and KSO white-light images (2009-2016, for SC 24). We useddifferent statistical methods and approaches to analyse cycle relatedvariations, solar cycle phase-related variations and long-term variations ofthe DR. $A$ and $B$ show statistically significant periodic variability. Thechanges in $A$ related to solar cycle phase are in accordance with previouslyreported theoretical and experimental results (higher $A$ during solar minimum,lower $A$ during the maximum of activity), while changes in $B$ differ from thetheoretical predictions as we observe more negative values of $B$, that is, amore pronounced DR during activity maximum. The main result of this paper forthe long-term variations in $A$ is the detection of a phase shift between theactivity flip (in the 1970s) and the equatorial rotation velocity flip (in theearly 1990s). During this time period both $A$ and activity show a seculardecreasing trend, indicating their correlation. Therefore, the theoreticalmodel fails in the phase-shift time period that occurs after the modernGleissberg maximum, while in the time period thereafter (after the 1990s),theoretical and experimental results are consistent. The long-term variationsin $B$ in general yield an anticorrelation of $B$ and activity, as a rise of$B$ is observed during the entire time period (1964-2016) we analysed, duringwhich activity decreased. We study for the first time the variation in solar DRand activity based on 53 years of KSO data. Our results agree well with theresults related to the solar cycle phase from corona observations.

Variation in solar differential rotation and activity in the period 1964-2016 determined by the Kanzelh\"ohe data set