Long-term Study of the Solar Filaments from the Synoptic Maps as Derived from a H Spectroheliograms of the Kodaikanal Observatory

Abstract

The century long ( 1914 – 2007 ) a H ( 656.28 nm ) spectroheliograms from the Kodaikanal Solar Observatory ( KSO ) have been recently digitized. Using these newly calibrated, processed images we study the evolution of dark elongated on-disk structures called fi laments, which are potential representatives of magnetic activities on the Sun. To our knowledge, this is the oldest uniform digitized data set with daily images available today in a H .We generate Carrington maps for the entire time duration and try to fi nd the correlations with maps of the same Carrington rotation from the Ca II K KSO data. Filaments are segmented from the Carrington maps using a semi- automated technique and are studied individually to extract their centroids and tilts. We plot the time-latitude distribution of the fi lament centroids, producing a butter fl y diagram which clearly shows the presence of poleward migration. We separate polar fi laments for each cycle and try to estimate the delay between the polar fi lament number cycle and the sunspot number cycle peaks. We correlate this delay with the delay between polar reversal and sunspot number maxima. This provides new insight on the role of polar fi laments on polar reversal.