Systematic Regularity of Solar Coronal Rotation During the Time Interval 1939-2019

TL;DR

This study analyzes 80 years of solar coronal rotation data, revealing a decreasing trend in rotation period, significant periodicities linked to solar cycles, and a complex phase relationship with magnetic activity.

Contribution

It provides a comprehensive analysis of long-term coronal rotation regularities and their connection to solar activity cycles using an extensive dataset.

Findings

Global coronal rotation period is about 27.5 days.

Coronal rotation accelerates over time.

Significant periods include 3.25, 6.13, 9.53, and 11.13 years.

Abstract

Temporal variation of the solar coronal rotation appears to be very complex and its relevances to the eleven-year solar activity cycle are still unclear. Using the modified coronal index for the time interval from 1939 January 1 to 2019 May 31, the systematic regularities of the 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 the periodic scales shorter than 64 days; (2) the coronal rotation period exhibit an obviously decreasing trend during the considered time interval, implying the solar corona accelerates its global rotation rate in the long run; (3) there exist significant periods of 3.25, 6.13, 9.53, and 11.13 years in the period length of the coronal rotation, providing an evidence that the coronal rotation should be connected with the quasi-biennial oscillation, the eleven-year solar cycle, and the 22-year Hale cycle (or the magnetic activity reversal); and (4) the phase relationship between the coronal rotation period and the 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 the phase, and the small mismatch in this band brings out the phase to drift. The possible mechanism for the above analysis results is discussed.