Chromospheric variations with solar cycle phase using imaging and spectroscopic studies

Abstract

Spectroscopic observations of Sun in Ca-K line profile were made as a function of latitude and integrated over the visible 180◦ longitude at the Kodaikanal observatory since 1985. The spectroheliograms of the Sun in Ca-K line have also been obtained at the observatory since 1907. We have derived Ca-K line parameters such as K1 and K2 widths and K-index averaged over regions 10◦ in latitude and 180◦ in longitudes from the spectroscopic studies and plage areas in these regions using the images of the Sun in Ca-K line. The comparison of Ca-K line widths with plage areas in respective latitude belts shows that small-scale activity due to network areas is very important in the study of irradiance variation with solar cycle phase. The K1 and K2 widths and K-index around 60◦ latitude belt show much less variation almost at the noise level during the solar cycle 22 and 23 as compared to other latitude belts and polar regions. These variations with latitude and time indicate the presence of two types of activity or flows. We infer the presence of counter flows in the polar regions and find that such type of analysis with better resolution and frequent observations will be very useful for solar cycle studies.