Mg II core-to-wing solar index from high resolution GOME data

The Mg II core-to-wing index was first developed for the Nimbus 7 polar backscatter ultraviolet spectrometer as an indicator of solar UV flux temporal variation. It is particularly important because of its long-term precision and insensitivity to instrument artifacts. For almost twenty years, solar activity monitoring from space has provided valuable data from which the Mg II index can be derived. The quality of each Mg II index is related to the calibration of the instrument as well as its spectral resolution. A reasonably good record can be obtained from the unresolved Mg II doublet at 280 nm. However, a higher spectral resolution of an instrument increases sensitivity to both the 27 days rotational modulation and the long term solar cycle variation. The new GOME instrument on board the ERS-2 satellite provides daily solar spectrum observations. Thanks to its high spectral resolution of 0.2 nm at 280 nm we can expect a very good Mg II index product from this instrument. In this paper, we show some preliminary results of GOME derived Mg II index using an algorithm taking into account its high spectral resolution. This algorithm is derived directly from UARS/SOLSTICE Mg II index algorithm at HAO and LASP. A direct comparison with the SOLSTICE index is also presented for a time period of half a year.