Differential rotation of sunspot groups in the period from 1874 through 1976 and changes of the rotation velocity within the solar cycle

Balthasar, H.; Vazquez, M.; Woehl, H.
Bibliographical reference

Astronomy and Astrophysics (ISSN 0004-6361), vol. 155, no. 1, Jan. 1986, p. 87-98. Research supported by the Consejo Superior de Investigaciones Cientificas.

Advertised on:
1
1986
Number of authors
3
IAC number of authors
2
Citations
227
Refereed citations
212
Description
An effort is made to determine the differential rotation of the sun on the basis of the complete sample (1874-1976) of the Greenwich Photoheliographic Results. In order to improve the representation of differential rotation, a modified fit formula whose constant lies at 15 deg latitude (where sunspots nearly always occur) is introduced. Rotation is noted to strongly depend on sunspot type, with C-groups exhibiting high velocities and H- and J-spots the lowest ones. The new fit formula indicates that the highest velocity is found around the minima; at the beginning of an activity maximum, there is a secondary velocity maximum. The lowest velocities lie between the activity maximum and minimum. The braking of recurrent sunspots is confirmed.