Temporal and latitudinal variations of Ca-K plage and network area: An implication to meridional flows

TL;DR

This study analyzes long-term variations in Ca-K plage and network areas across latitudes, revealing phase shifts and anti-correlations with sunspot activity, suggesting complex meridional flow patterns in the solar convection zone.

Contribution

It provides new insights into the latitudinal and temporal behavior of solar chromospheric features and proposes the existence of multi-cell meridional flows based on phase difference analysis.

Findings

Activity begins at ~45° latitude and shifts towards equator at ~9.4 m/sec.

No phase difference at 55°, 65°, 75° latitudes indicates simultaneous changes.

Polar activity is anti-correlated with sunspot number.

Abstract

The Ca-K spectroheliograms obtained at the Kodaikanal observatory (KO) are used to generate a uniform time series using the equal contrast technique (ECT) to study the long and short-term variation in the solar chromosphere. The percentage of plage, Enhanced network (EN), Active network (AN), and Quiet network (QN) area at various latitudes is compared with the activity at 35$^{\circ}$ latitude and also with the sunspot number for the period of 1907 -- 1984. The values of phase differences indicate that the activity begins at $\sim$45$^{\circ}$ latitude and shift progressively to the lower latitude at a speed of $\sim$~9.4~m~sec$^{-1}$ . The shift speed slows down gradually and reaches $\sim$~3~m~sec$^{-1}$ at $\sim$5$^{\circ}$ latitude. No phase difference between the variations of Ca-K activity at 55$^{\circ}$, 65$^{\circ}$, and 75$^{\circ}$ latitude belts implies that changes in the activity are happening simultaneously. The analysis shows that the activity at polar latitude belts is anti-correlated with the sunspot number. This study indicates that a multi-cell meridional flow pattern could exist in the solar convection zone. One type of cell could transport the magnetic elements from mid-latitude to low-latitude belts through meridional flows, and the other one could be operating in the polar region.