Measurement of Kodaikanal white-light images - IV. Axial tilt angles of sunspot groups

The Kodaikanal sunspot data set, covering the interval 1906-1987, is used i n conjunction with the similar Mount Wilson sunspot data set, covering the interval 1917-1985, to examine characteristics of sunspot group axial tilt angles. Good agreement is demonstrated between various results derived from the two independent data sets. In particular, the tendency for sunspot gro ups near the average tilt angle to be larger than those far from the averag e tilt angle is confirmed. Similarly the faster residual rotation rate for groups near the average tilt angle is also confirmed. Other confirmations a re made for the relationships between latitude drift of sunspot groups and tilt angle, polarity separations, and axial expansion. Evidence is presente d that tilt angles averaged over these long time intervals differ between t he north and south hemispheres by about 1.4 deg. It is suggested that resid ual tilt angles show a slight systematic variation with phase in the activi ty cycle.