# Signature of Extended Solar Cycles as Detected from Ca II K Synoptic Maps of Kodaikanal and Mount Wilson Observatory

## TL;DR

This study analyzes long-term Ca II K spectroheliograms from Kodaikanal and Mount Wilson to detect signatures of Extended Solar Cycles through quiet sun features, revealing overlapping cycles and equator-ward branch dynamics.

## Contribution

It introduces a method to identify Extended Solar Cycles using historical Ca II K data, focusing on quiet sun network bright elements, which enhances understanding of solar cycle overlap.

## Key findings

- Detected overlapping extended cycles in historical data.
- Identified equator-ward branch progression taking about 15 years.
- Demonstrated the presence of cycle signatures in quiet sun features.

## Abstract

In the recent years there has been a resurgence of the study of Extended Solar Cycles (ESCs) through observational proxies mainly in Extreme Ultraviolet. But most of them are limited only to space-based era covering only about two solar cycles. Long-term historical data-sets are worth in examining the consistency of ESCs. Kodaikanal Solar Observatory (KSO) and Mount Wilson Observatory (MWO) are the two major sources of long-term Ca II K digitised spectroheliograms covering the temporal spans 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 datasets. Subsequently we excluded the plage areas to consider only quiet sun (QS) and detected small scale bright features through intensity thresholding over the QS network. Latitudinal density of those features, which we named as `Network Bright Elements' (NBEs), could clearly depict the existence of overlapping cycles with equator-ward branches starting at latitude $\approx 55^{\circ}$ and taking about $15\pm1$ years to reach the equator. We performed superposed epoch analysis to depict the similarity of those extended cycles. Knowledge of such equator-ward band interaction, for several cycles, may provide critical constraints on solar dynamo models.