SOLSTICE II -- Magnesium II M. Snow 1*, J. Machol 2,3, R. Viereck 4, M. Weber 5, E. Richard 1 1 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA; 2 NOAA/National Geophysical Data Center, Boulder, Colorado, USA; 3 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA; 4 NOAA Space Weather Prediction Center, Boulder, Colorado, USA; 5 Institute of Environmental Physics, University of Bremen, Bremen, Germany The Mg II index as a proxy for solar EUV variability The Mg II index is based on the ratio of irradiances of highly variable chromospheric lines to stable photospheric emissions all near 280 nm. It has been shown to be a good proxy for solar UV, EUV, and the facular brightening component of the Total Solar Irradiance. Mg II Index Measurements Timeline GC51C-0979 The Magnesium II core-to-wing index is a critical proxy for solar chromospheric variability. The SOLar-STellar Irradiance Comparison Experiment II (SOLSTICE II) has been making this measurement since launch in Recent analysis comparing the primary channel measurement to the backup channel has indicated that an instrument artifact was introduced in early This poster will describe the magnitude of the artifact and present the corrected time series. We will compare the corrected dataset to the other Mg II data records over the past ten years. Solar EUV and the thermosphere/ionosphere At Earth, solar irradiance at various wavelengths is absorbed preferentially at various altitudes. The primary energy input into the upper atmosphere is EUV which heats the thermosphere and creates the ionosphere. Variations in EUV flux drive the chemistry and dynamics of the thermosphere and ionosphere. EUV has high variability on many time scales (secs to years). EUV data is needed for thermospheric/ ionospheric models which provide information about satellite drag, communications, navigation systems, and upper atmospheric chemistry. Atmospheric absorption as a function of wavelength (reds and blues). Also shown are the solar spectrum (white line on a log scale) and Earth's atmospheric temperature profiles (orange and yellow lines). EUV nm XUV (soft x rays) nm Comparison through Solar Minimum This chart shows the available measurements of the Magnesium II index during the most recent solar minimum. The three NOAA missions use SBUV/2 instruments with 1.1 nm spectral resolution. GOME, SCIAMACHY, and GOME-2 have resolutions around 0.3 nm, and SOLSTICE has a spectral resolution of 0.1 nm. The instruments shown all measure the MgII feature at least once per day. Other instruments such as OMI and SOLSPEC will be used in building a new long-term composite (Snow et al. in preparation). After comparisons between the two SOLSTICE instruments on SORCE and the Bremen composite, we determined that the SOLSTICE A data had an artifact starting in January We have now corrected the SOLSTICE A data using measurements from SOLSTICE B. The SOLSTICE MgII index now is in good agreement with the Bremen composite. Details of this correction are described in: Snow, M., Weber, M., Machol, J., Viereck, R., and Richard, E. (2013) Comparison of Magnesium II Core-to-Wing Ratio Observations During Solar Minimum 23/24, Journal of Space Weather and Space Climate (accepted).