ABSTRACT
In this paper, we report evidence of a very strong and statistically significant relationship between hemispheric asymmetry in the solar coronal rotation rate and solar activity. Our approach is based on the cross-correlation of the hemispheric asymmetry index (AI) in the rotation rate with annual solar activity indicators. To obtain the hemispheric asymmetry in the solar rotation rate, we use solar full disc (SFD) images at 30.4-, 19.5- and 28.4-nm wavelengths for the 24th solar cycle, that is, for the period from 2008 to 2018, as recorded by the Solar Terrestrial Relations Observatory (STEREO) space mission. Our analysis shows that the hemispheric asymmetry in rotation rate is high during the solar maxima from 2011 to 2014. However, hemispheric asymmetry decreases gradually on both sides (i.e. from 2008 to 2011 and from 2014 to 2018). The results show that the AI leads sunspot numbers by ∼ 1.56 yr. This is a clear indication that hemispheric asymmetry triggers the formation of sunspots in conjunction with the differential rotation of the Sun.
Time Dependence of the Solar Rotation Rate
