Solar Chromospheric Variability from the National Solar Observatory (NSO)

Observations of the disk-integrated solar Ca II K-line are made using
the Evans Coronal Facility at The National Solar Observatory/
Sacramento Peak. A coelostat is used to feed the horizontal Littrow
spectrograph and the spectrum from 3898-3954 angstroms is recorded by
scanning the grating and digitizing the output of a photomultiplier.
About 50-150 spectral scans are made each day. From 1976-1983 data
was obtained on 10% of all days, while from 1984-present data is
obtained on about 45% of all days.

For more information see:

http://www.sunspot.noao.edu/nsosp/data/cak_mon.html

Data are also available from NOAA/NESDIS/NGDC Solar-Terrestrial
Physics Program at:
http://www.ngdc.noaa.gov/stp/stp.html