Abstract:
In our previous article (Priyal et al. in Solar Phys. 289, 127, 2014) we have discussed the details of observations and methodology adopted to analyze the Ca-K spectroheliograms obtained at the Kodaikanal Observatory (KO) to study the variation of Ca-K plage
areas, enhanced network (EN), and active network (AN) for Solar Cycles, namely 19, 20,
and 21. Now, we have derived the areas of chromospheric features using KO Ca-K spectroheliograms to study the long-term variations of Solar Cycles 14 to 21. The comparison of
the derived plage areas from the data obtained at the KO observatory for the period 1906 –
1985 with that of MWO, NSO for the period 1965 – 2002, earlier measurements made by
Tlatov, Pevtsov, and Singh (Solar Phys. 255, 239, 2009) for KO data, and the SIDC sunspot
numbers shows a good correlation. The uniformity of the data obtained with the same instrument remaining with the same specifications provided a unique opportunity to study longterm intensity variations in plages and network regions. Therefore, we have investigated the
variation of the intensity contrast of these features with time at a temporal resolution of six
months assuming that the quiet-background chromosphere remains unchanged during the
period 1906 – 2005 and found that the average intensity of the AN, representing the changes
in small-scale activity over solar surface, varies with solar cycle being less during the minimum phase. In addition, the average intensity of plages and EN varies with a very long
period having a maximum value during Solar Cycle 19, which was the strongest solar cycle
of twentieth century.
