Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019

Theodosios Chatzistergos, Ilaria Ermolli, Natalie A. Krivova +16

We derive the plage area evolution over the last 12 solar cycles employing data from all Ca II K archives available publicly in digital form known to us, including several as yet u…