Systematic regularity of solar coronal rotation during the time interval 1939–2019

Abstract

ABSTRACT The temporal variation of solar coronal rotation appears to be very complex and its relevance to the 11-year solar activity cycle is still unclear. Using the modified coronal index for the time interval from 1939 January 1–2019 May 31, the systematic regularities of solar coronal rotation are investigated. Our main findings are as follows. (1) From a global point of view, the synodic coronal rotation period with a value of 27.5 days is the only significant period at periodic scales shorter than 64 days. (2) The coronal rotation period exhibits an obvious decreasing trend during the time interval considered, implying that the solar corona accelerates its global rotation rate in the long run. (3) Significant periods of 3.25, 6.13, 9.53 and 11.13 years exist in coronal rotation, providing evidence that coronal rotation should be connected with the quasi-biennial oscillation, the 11-year solar cycle and the 22-year Hale cycle (or magnetic activity reversal). (4) The phase relationship between the coronal rotation period and solar magnetic activity is not only time-dependent but also frequency-dependent. For a small range around the 11-year cycle band, there is a systematic trend in phase and a small mismatch in this band causes the phase to drift. The possible mechanism for the above analysis results is discussed.