Variations of the Ca II K Line Profile Parameters with Solar Latitude and Time Observed from Kodaikanal Solar Observatory

TL;DR

This study analyzes ten years of Ca II K line profile data from Kodaikanal Solar Observatory, revealing latitudinal and temporal variations linked to solar magnetic activity and asymmetries.

Contribution

It provides detailed measurements of Ca II K line parameters over time and latitude, highlighting asymmetries and correlations with solar activity indicators.

Findings

Parameters increase asymmetrically towards higher latitudes, especially in the southern hemisphere.

Certain line parameters correlate positively with solar plage and spot filling factors.

Distinct latitudinal peaks in line parameters relate to solar magnetic activity distribution.

Abstract

The Calcium-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 ten years to study the variations in the Ca II K line profiles recorded between 2015 and 2024, of which 709 days of data were found useful. The temporal and time-averaged latitudinal variations of the K$_{1}$ width, K$_{2}$ width, K$_{3}$ intensity and the intensity ratios of K$_{2v}$/K$_{2r}$ and K$_{2v}$/K$_{3}$ 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$_{1}$ width and K$_{3}$ intensity showed positive correlations with the plage and spot filling factors, whereas the temporal plots for K$_{2}$ width, K$_{2v}$/K$_{2r}$ and K$_{2v}$/K$_{3}$ intensity ratios showed negative correlations. The time-averaged latitudinal plot for K$_{1}$ width has small peaks near 25{\deg}N and 20{\deg}S. The K$_{2}$ width has a small peak at 0{\deg}. The K$_{3}$ intensity has peaks at 20{\deg}N and 15{\deg}S. The K$_{2v}$/K$_{2r}$ intensity ratio shows peaks at 50$\degree$N, 0{\deg} and 40{\deg}S. The K$_{2v}$/K$_{3}$ intensity ratio shows peaks at 60{\deg}N, 0{\deg} and 60{\deg}S. Slope profiles show spectral response to magnetic activity peaks near K$_{3}$ with north-south asymmetries. Such variations in the line profiles are important in the studies of solar irradiance, surface flux transport and solar dynamo.