Study of solar chromosphere Variation of Calcium K line profiles with solar cycle

Abstract

The various features on the solar surface like sunspots, plages, network, active network play a main role in the solar variability. This thesis uses observations which were started in an effort to delineate the role of various features such as plages and networks in the variations of Sun with solar cycle. During 1970s, a new programme to study long term variability of solar chromosphere was started by several researchers. They used Ca-K line profiles of Sun as a star as diagnostic tool to study the long term variability of solar chromosphere. Skumanich et al.(1984) proposed a three component model using cell, network and plage areas and using extant laws of limb darkening. During minimum phase of the Sun they were able to reconstruct the observed Ca-K line profile with the contribution from cell and network. But during active phase, the addition of plage component was found to be insufficient to fit the model with observed profiles. Therefore, existence of excess component called as Active network component was introduced during the active phase. Whereas White and Livingston (1978) found no variation in the centre of solar disc with respect to solar cycle phase. Hence, this excess component may be from higher latitudes. In view of the differences in the results of model for the variation of solar activity and observations, a new technique of observing the Sun was planned to take Ca-K line profiles as a function of latitude and integrated over visible longitude since 1986 at kodaikanal Solar Tunnel Telescope on day to day basis for the long period. Which means at each latitude we get the integrated flux over the 180 degree longitudes from all the features like cell, network, plage and active network. The spectra obtained on 807 days were found to be useful and rest of the observations for about 400 days were discarded due to existence of passing clouds which effected the profiles due to scattering of light. On some days spectra of Sun as a star have also been obtained. The variations in sky transparency are