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 K1 width, K2 width, K3 intensity and the intensity ratios of K2v/K2r and K2v/K3 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 K1 width and K3 intensity showed positive correlations with the plage and spot filling factors, whereas the temporal plots for K2 width, K2v/K2r, and K2v/K3 intensity ratios showed negative correlations. The time-averaged latitudinal plot for K1 width has small peaks near 25◦N and 20◦S. The K2 width has a small peak at 0◦. The K3 intensity has peaks at 20◦N and 15◦S. The K2v/K2r intensity ratio shows peaks at 50◦N, 0◦, and 40◦S. The K2v/K3 intensity ratio shows peaks at 60◦N, 0◦, and 60◦S. Slope profiles show spectral response to magnetic activity peaks near K3 with north–south asymmetries. Such variations in the line profiles are important in the studies of solar irradiance, surface flux transport, and solar dynamo.