Variations of the Ca ii K line profile parameters with solar latitude and time observed from Kodaikanal Solar Observatory

Abstract

The Ca-K line profiles as functions of solar latitude and time were obtained through our observations from the Kodaikanal Solar Observatory using the solar tunnel telescope and spectrograph with a CCD detector. Observations were conducted on all days with favourable sky conditions. We analysed the data collected over a period of about 10 yr to study the variations in the Ca ii K line profiles recorded between 2015 and 2024, of which 709 d of data were found useful. The temporal and time-averaged latitudinal variations of the K width, K width, K intensity and the intensity ratios of K/K and K/K were computed using a semi-automated program. The parameters showed asymmetric increases towards the higher latitudes, with the rates of increase being higher in the Southern hemisphere. The temporal plots for K width and K intensity showed positive correlations with the plage and spot filling factors, whereas the temporal plots for K width, K/K, and K/K intensity ratios showed negative correlations. The time-averaged latitudinal plot for K width has small peaks near 25N and 20S. The K width has a small peak at 0. The K intensity has peaks at 20N and 15S. The K/K intensity ratio shows peaks at 50N, 0, and 40S. The K/K intensity ratio shows peaks at 60N, 0, and 60S. Slope profiles show spectral response to magnetic activity peaks near K with north-south asymmetries. Such variations in the line profiles are important in the studies of solar irradiance, surface flux transport, and solar dynamo. © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.