Signature of extended solar cycles as detected from Ca II K synoptic maps of Kodaikanal and Mount Wilson Observatory

But most of them are limited only to the space-based era covering only about two solar cycles. Long-term historical data sets are worth examining for the consistency of ESCs.

The Kodaikanal Solar Observatory (KSO) and the Mount Wilson Observatory (MWO) are two major sources of long-term Ca II K digitized spectroheliograms covering the temporal spans of 1907-2007 and 1915-1985 respectively. In this study, we detected supergranule boundaries, commonly known as networks, using the Carrington maps from both KSO and MWO data sets. Subsequently we excluded the plage areas to consider only the quiet Sun (QS) and detected small-scale bright features through intensity thresholding over the QS network.