The Mg II Solar Activity Proxy Indicator Derived from GOME and SCIAMACHY

The main purpose of the passive remote sensing instruments GOME and SCIAMACHY is to determine the amount and distribution of a large number of atmospheric trace constituents by measuring Earthshine radiance. In addition solar observations are performed on a regular time grid which offer the possibility to monitor solar variations. This paper summarises the derivation of a proxy solar activity indicator from GOME and SCIAMACHY solar irradiance measurements. This combined GOME/SCIAMACHY Mg II index is compared with the composite NOAA Mg II index (1978-present) showing an excellent correlation of 0.991. It is, therefore, well suited to be combined with these data to establish a long-term time series spanning almost three 11 year solar cycles.