Solar activity during solar cycle 23 monitored by GOME

Abstract

The daily solar spectral measurements by the Global Ozone Monitoring Experiment (GOME) aboard ERS2 are well suited to track solar activity by looking at irra- diance changes in the center of selected Fraunhofer lines. The major modulation of the irradiance changes con- tain periodicity of about 27-28 days, corresponding to the mean solar rotation period, and eleven years due to solar activity associated with the 22-year magnetic cycle of the sun. The MgII doublet at 280nm and the CaII K line at around 395nm have been analysed to derive a proxy so- lar activity indicator time series from GOME starting in July 1995 near the end of the declining phase of solar cycle 22. GOME is currently observing the onset of solar cycle 23. An excellent correlation with solar observations provided by the UARS instrument SUSIM (Solar Ultravi- olet Spectral Irradiance Monitor) has been achieved after removing instrumental artefacts such as UV degradation and etaloning from the GOME level-1 spectra. An esti- mate of solar UV irradiance variability with a change in the GOME MgII index is given.