Using the Solar Optical Observing Network ( SOON ) sunspot-group data for the period 1985 – 2010 , the variations in the annual mean equatorial-rotation rates of the sunspot groups are determined and compared with the known variations in the solar equatorial-rotation rates determined from the following data : i ) the plasma rotation rates at 0.94R _ { \odot } , 0.95R _ { \odot } , …,1.0R _ { \odot } measured by Global Oscillation Network Group ( GONG ) during the period 1995 – 2010 , ii ) the data on the soft X-ray corona determined from Yohkoh /SXT full disk images for the years 1992 – 2001 , iii ) the data on small bright coronal structures ( SBCS ) which were traced in Solar and Heliospheric Observatory ( SOHO ) /EIT images during the period 1998 – 2006 , and iv ) the Mount Wilson Doppler-velocity measurements during the period 1986 – 2007 .
A large portion ( up to \approx 30 ^ { \circ } latitude ) of the mean differential-rotation profile of the sunspot groups lies between those of the internal differential-rotation rates at 0.94 R _ { \odot } and 0.98 R _ { \odot } .
The variation in the yearly mean equatorial-rotation rate of the sunspot groups seems to be lagging that of the equatorial-rotation rate determined from the GONG measurements by one to two years .
The amplitude of the latter is very small .
The solar-cycle variation in the equatorial-rotation rate of the solar corona closely matches that determined from the sunspot-group data .
The variation in the equatorial-rotation rate determined from the Mount Wilson Doppler-velocity data closely resembles the corresponding variation in the equatorial-rotation rate determined from the sunspot-group data that included the values of the abnormal angular motions ( > | 3 ^ { \circ } | day ^ { -1 } ) of the sunspot groups .
Implications of these results are pointed out .