Coronal Dynamic Activities in the Declining Phase of a Solar Cycle

TL;DR

This study investigates solar dynamic activities during the declining phase of a solar cycle, revealing increased coronal hole activities and mass ejections, indicating extended magnetic flux motions beyond the sunspot minimum.

Contribution

It provides new insights into the timing and nature of solar dynamic activities, emphasizing their prominence in the declining phase of the solar cycle.

Findings

Coronal hole areas show a second maximum in the declining phase.

Coronal hole splitting and merging events are more frequent in the declining phase.

Coronal mass ejections are over-populated during the declining phase.

Abstract

It has been known that some solar activity indicators show a double-peak feature in their evolution through a solar cycle, which is not conspicuous in sunspot number. In this letter, we investigate the high solar dynamic activity in the declining phase of the sunspot cycle by examining the evolution of polar and low latitude coronal hole areas and the statistics of splitting and merging events of coronal holes and coronal mass ejections detected by SOHO/LASCO C3 in solar cycle 23. Although the total coronal hole area is at its maximum near the sunspot minimum, in which polar coronal holes prevail, it shows a comparable second maximum in the declining phase of the cycle, in which low latitude coronal holes are dominant. The events of coronal hole splitting or merging, which are attributed to surface motions of magnetic fluxes, are also mostly populated in the declining phase of the cycle. The far-reaching C3 coronal mass ejections are also over-populated in the declining phase of the cycle. From these results we suggest that solar dynamic activities due to the horizontal motions of magnetic fluxes extend far in the declining phase of the sunspot cycle.