The solar corona in cycle 23 Original Research Article

The Coronal Diagnostic Spectrometer (CDS) on SOHO has been recording EUV spectra and monitoring time variability of EUV line intensities, electron temperature and density in the low solar corona during the rising part of Cycle 23. The four-year data set includes daily synoptic observations in four EUV lines along the central meridian since April 1996 and weekly diagnostic observations above the polar coronal holes since July 1997. The history of line intensities along the central meridian, and radial profiles of electron temperature and density above the polar regions at heights up to 1.15R⊙ are derived. EUV line intensities and photospheric magnetic flux are also calculated for 50 active regions observed from 1996 to June 1998. Variability of temperature, density, and EUV spectral line intensities in the polar coronal holes, quiet sun and active regions with the solar cycle is discussed. Power-law relationships among the EUV line intensities from the CDS synoptic data, and also between the EUV line intensities and magnetic field flux in active regions are presented.