Recurring coronal holes and their rotation rates during the solar cycles 22–24

Abstract

Coronal holes (CHs) play a significant role in making the Earth geo-magnetically active during the declining and minimum phases of the solar cycle. In this study, we analysed the evolutionary characteristics of the Recurring CHs from the year 1992 to 2016. The extended minimum of Solar Cycle 23 shows unusual characteristics in the number of persistent coronal holes in the mid- and low-latitude regions of the Sun. Carrington rotation maps of He 10830 Å and EUV 195 Å observations are used to identify the Coronal holes. The latitude distribution of the RCHs shows that most of them are appeared between $\pm 20^{\circ }$ latitudes. In this period, more number of recurring coronal holes appeared in and around $100^{\circ }$ and $200^{\circ }$ Carrington longitudes. The large sized coronal holes lived for shorter period and they appeared close to the equator. From the area distribution over the latitude considered, it shows that more number of recurring coronal holes with area $<10^{21}~\mbox{cm}^{2}$ appeared in the southern latitude close to the equator. The rotation rates calculated from the RCHs appeared between $\pm 60^{\circ }$ latitude shows rigid body characteristics. The derived rotational profiles of the coronal holes show that they have anchored to a depth well below the tachocline of the interior, and compares well with the helioseismology results.