Ilaria Ermolli (INAF OAR) Natalie A. Krivova (MPS) Sami K. Solanki (MPS)
Solar activity and variability driven by the magnetic field on the Sun affect Earth's space environment and climate. Magnetic regions on the solar surface are observed as dark sunspots and bright faculae or plage and network. Long-term studies of solar activity and variability typically rely on records of sunspot observations, going back to the beginning of the 17th century although with deteriorating quality. Significant effort has been invested to put the records by individual observers into a consistent composite. Full-disc photographs of the Sun showing plage have been taken since the late 19th century, and in contrast to sunspots, no equivalent composite series for plage areas exists. This is primarily because of the numerous issues plaguing the Ca II K observations as well as the lack of their photometric calibration. Thus, most studies of Ca II K data used photometrically uncalibrated images and were restricted to single archives. Furthermore, due to differences in the analysed data and the methods, the published time series of plage areas show partly controversial results. We have developed a method to calibrate and process Ca II K observations and applied it consistently to multiple series covering the period 1893-2018. We have identified plage regions in the analysed images and studied the temporal evolution of the plage areas in each archive. The results from all the series have then been cross-calibrated based on their daily statistics and stitched together to produce the first composite of plage areas. The obtained composite describes the evolution of the bright magnetic regions over the period 1893-2018, complementing our knowledge of the evolution of magnetic regions over the last century.
Mode of presentation: oral (Need to be confirmed by the SOC)