The NOAA SBUV MgII c/w measurement has been an important input to solar irradiance models, and is one of the best chromospheric time series available for describing solar irradiance variations from daily to solar cycle timescales. Continuous daily values are available from 1978, covering nearly three solar cycles (see below). In many ways, compared to sunspots and the F10.7 2800 MHz data, it is a superior index to solar variability and space weather because it can accurately describe chromosphere variability on time scales ranging from a solar rotation (27 days) to the 11-year solar cycle, and because it describes the solar EUV variability that directly affects the Earth's thermospheric density, unlike F10.7 and sunspots.
The SBUV instrument (Solar Backscatter Ultraviolet) has been on-board all of the NOAA-9 to NOAA-18 polar-orbiting satellites. The main purpose of the SBUV instrument is to monitor terrestrial ozone. However, it also acquires solar UV spectral irradiance. One component of these solar irradiance data is the daily Mg II center-to-wing ratio (MgII c/w), which is a relative photometric measurement at 280 nm between the Mg II h and k lines. Because it is based on the ratio of the lines, and not to an absolute calibration, it is much less susceptible to instrument degradation. However, there are other instrument and satellite effects that need to be accounted for in deriving the ratio.
NOAA National Environmental Satellite, Data, and Information Service (NESDIS) monitors the satellites, and provides the unprocessed data to the NOAA Space Weather Prediction Center (SWPC). In the past, NOAA/SWPC produced a calibrated data file of Mg II c/w data and those data are in the process of being re-calibrated.
Update: 13 Dec 2011
There have been a number of difficulties in determining an accurate Mg II c/w since approximately February 2009. The SBUV diffuser plate on NOAA-17 increasingly was shadowed due to the spacecraft's attitude, due to it's slow precession in it's orbit. SET Mg II data operations substituted a combination of adjusted SOLSTICE and GOME data, but the data were not consistently accurate (to within the 5% level).
Recently, Matt DeLand at SSAI has graciously provided new processing algorithms for the NOAA-18 data, which has been performing very well. SET has integrated those new algorithms in it's operations 13 Dec 2011. These data have been re-calibrated back to June 1, 2008. Prior to that, the data is unchanged from earlier versions. In the most recent version, NOAA-18 is the primary source, and when those measurments are missing, data from the SOLSTICE instrument are substitued in. Users of the SET V4 Mg II c/w are asked to credit Space Environment Technologies.
Near real-time SET Mg II c/w data are available at: http://sol.spacenvironment.net/~spacewx/data/mg2_atmos.dat.txt.
Below are links to miscellaneous plots and data related to operations (and are not intended for official use):
| cur_nesdis_N18_mg2.jpg (scan data) | reported_NESDIS_N18.txt | Mg2_N18_vs_ATM.jpg(historical) |
| reported_solstice.txt | filtered_solstice.txt | |
| mg2_SET_v4.dat.txt | mg2_SET_v4.jpg | mg2_combined_scatter.jpg |
