Signature of differential rotation in solar disk-integrated chromospheric line emission

Abstract

UARS SOLSTICE data have been subjected to Fourier and wavelet analyses in order to search for the signature of the solar rotation law in the disk-integrated irradiance of UV lines. Lyman-α, Mg II, and Ca II data show a different behaviour. In the SOLSTICE data there are significant temporal variations of the rotation rate of the UV tracers over 5—6 years. Often several distinct rotation periods appear almost simultaneously. Beside the basic period around 27 days there are signals at 32—35 days corresponding to the rotation rate at very high latitudes. For more than 5 years during another period of the solar cycle the rotational behaviour is quite different; there is an indication of differential rotation of active regions in these Ca II ground-based data. The data contain a wealth of information about the solar differential rotation, but it proves difficult to disentangle the effects of the different emitting sources.