Measurement of Kodaikanal white-light images - V. Tilt-angle and size variations of sunspot groups

We examine here the variations of tilt angle and polarity separation (as de fined in this paper) of multi-spot sunspot groups from the Kodaikanal and M ount Wilson data sets covering many decades. We confirm the tilt-angle chan ge vs tilt-angle result found earlier from the Mount Wilson data alone. Sun spot groups tend on average to rotate their axes toward the average tilt an gle. We point out that if we separate groups into those with tilt angles gr eater than and less than the average value, they show tilt-angle variations that vary systematically with the growth or decay rates of the groups. Thi s result emphasizes again the finding that growing (presumably younger) sun spot groups rotate their magnetic axes more rapidly than do decaying (presu mably older) groups. The tilt-angle variation as a function of tilt angle d iffers for those groups whose leading spots have greater area than their fo llowing spots and vice versa. Tilt-angle changes and polarity separation ch anges show a clear relationship, which has the correct direction and magnit ude predicted by the Coriolis force, and this strongly suggests that the Co riolis force is largely responsible for the axial tilts observed in sunspot groups. The distribution of polarity separations shows a double peak. Thes e peaks are perhaps related to super- and meso-granulation dimensions. Grou ps with polarity separations less than 43 Mm expand on average, while those groups with separations more than this value contract on average. We prese nt evidence that the rotation of the magnetic axes of sunspot groups is abo ut a location closer to the following than to the leading sunspots.