Solar Calcium Plage Data
Solar observatories have monitored the Sun in the calcium (Ca) K line wavelength by using a filter that allows only this wavelength's light through, calcium filtergrams, or spectroheliograms. Daily full disk calcium K232 images are reduced to provide calcium plage positions and areas or summed to produce a daily Ca K index. Ca K active regions can be seen moving across the solar disk, above the white light sunspot regions, and higher in the solar atmosphere (chromosphere).
Daily Calcium Plage Areas and Network Areas from Mt. Wilson Observatory Apn Data 1915-1999 -- Peter Foukal
The following Ap daily data (no network included) are corrected for foreshortening, and so are expressed in fraction of a hemisphere. It is important to stress that these are just areas of the Active Region (AR) plages -- just like the McMath Plage Index (except the McMath Index incorporates estimates of brightness, whereas Ap is just area). The reference for these data is the GRL 23, 2169 (1996) paper by P. Foukal. Both the McMath index and the Ap are of limited use now that the Apn (area of plage plus active network) is available.
San Fernando Observatory K-line facular data -- Gary Chapman
Daily calcium plage reduced data, including position, areas and intensities
Solar observatories contributing to this database include McMath Solar Observatory (1942-Sep 1979), Hale Observatory (Mt. Wilson Solar Observatory -- Oct 1979-Sep 1981), and Big Bear Solar Observatory (Oct 1981-Oct 1987)
Daily summary data of the McMath/Hale/BigBear database 1942-1987Includes YYMMDD, number of plage regions, total corrected plage area, and Calcium plage index for that day.
Big Bear Solar Observatory Calcium K Index
Sacramento Peak Solar Observatory Daily Calcium K Index
Solar-Geophysical Data Regions of Solar Activity Table 1969-1982. Daily white light sunspot regions are tied to the overlying Ca K plage regions each day.