Temporal and Latitudinal Variations in Ca-K Plage and Network Area: An Implication for Meridional Flows

Abstract

The Ca-K spectroheliograms obtained at the Kodaikanal observatory are used to generate a uniform time series using the equal-contrast technique for studying the long- and short-term variations in the solar chromosphere. The percentages of plage, enhanced network, and active and quiet network areas at various latitudes is compared with the activity at 35° latitude and also with the sunspot number for the period of 1907–1984. The values of the phase differences indicate that the activity begins at ∼45° latitude and shifts progressively to a lower latitude at a speed of ∼9.4 m s−1 . The shift speed slows down gradually and reaches ∼3 m s−1 at ∼5° latitude. No phase difference between the variations of Ca-K activity at 55°, 65°, and 75° latitude belts implies that changes in the activity are happening simultaneously. The analysis shows that the activity at polar latitude belts is anticorrelated with the sunspot number. This study indicates that a multicell meridional flow pattern could exist in the latitude direction. One type of cell could transport the magnetic elements from mid- to low-latitude belts through meridional flows, and the other cell type could be operating in the polar region.

Equator to Pole Solar Chromospheric Differential Rotation Using Ca-K Features Derived from Kodaikanal Data

“…The contrast of the images in the time series was made uniform by applying the ECT methodology (Singh et al 2021). The Ca-K features, such as plages, EN, AN, and QN regions, were segregated based on intensity and area threshold values in the different latitude belts with an interval of 10°up to 90° (Priyal et al 2023). In panel (a) of Figure 1, we present an example of the analyzed Ca-K image taken on 1936 April 11.…”