Observations of Solar Activity (Mg II Index) by GOME, SCIAMACHY, and GOME-2

Mg II index data

The Mg II data are derived from GOME (1995-2011), SCIAMACHY (2002-2012), GOME-2A (2007-present), and GOME-2B (2012-present). All three data sets as well as the Bremen Mg II composite data are available (see links below). In late years the GOME solar irradiance has degraded to about 20% of its value near 280 nm in 1995, so that the GOME data have become noisier. The most recent information on our Mg II data can be found in Snow et al. (2014).

Data download

Additional information and plots

The emission core of the Mg II doublet (280 nm) exhibits the largest natural solar irradiance variability above 240 nm. It is frequently used as a proxy for spectral solar irradiance variability from the UV to EUV associated with the 11-yr solar cycle (22-yr magnetic cycle) and solar rotation (27d).

Figure 1 shows the Mg II data from GOME-2A (since 2007) and GOME-2B (since 2012) from the last two months.

Figure 2 shows the Mg II indices derived from GOME (1996-2011), SCIAMACHY (2002-2012), and both GOME-2' (2007-present) as calculated by us.

By combining data from different satellites a composite Mg II index can be derived that covers more than three solar cycles as shown in Figure 3.

In Figure 4 the solar activity from the three most recent solar cycles (22-24) are directly compared.

Figure 1. Mg II core-to-wing ratios from GOME-2A and GOME-2B from the last two months.

Figure 2. Mg II core-to-wing ratio from GOME, SCIAMACHY, GOME-2A, and GOME-2B.

Figure 3. Composite Mg II index ('Bremen composite'). Values indicated are the numbers of days for each satellite contributing to the composite index. Missing values were filled using scaled F30 cm radio flux data (http://solar.nro.nao.ac.jp/norp/html/daily_flux.html). The black curve shows the timeseries twice smoothed with a 55-day boxcar. Bottom panel shows the estimated uncertainty of the composite Mg II index. Higher uncertainties are due to the interpolated F30cm flux values. The solar minimum to maximum change in this Mg II index is about 14% of the long-term mean as derived from the smoothed Mg II time series. This means that the uncertainty of the Mg II index with respect to a typical solar cycle change is about 2% and higher.

Figure 4. Comparison of UV solar activity in the three most recent solar cycles (SC) 22-24. The thick curves show the Mg II index timeseries twice smoothed with a 55-day boxcar. Dates of minima of solar cycles (YYYYMMDD) were determined from the smoothed Mg II index.


Cebula, R.P., and M.T. DeLand, 1998: Comparisons of the NOAA11 SBUV/2, UARS SOLSTICE, and UARS SUSIM MgII solar activity proxy indices, Sol. Phys. 177, 117-132

DeLand, M.T., and R. P. Cebula, 1998: Solar UV activity at solar cycle 21 and 22 minimum from NOAA 9 SBUV2 data, Sol. Phys. 177, 105-116.

DeLand, M.T., and R. P. Cebula, 1993: Composite MgII solar activity index for solar cycles 21 and 22, J. Geophys. Res. 98, 12809-12823.

DeLand, M., and S. Marchenko, 2013: The solar chromospheric Ca and Mg indices from Aura OMI, J. Geophys. Res. Atmos., 118, 3415-3423, doi:10.1002/jgrd.50310.

de Toma, G., et al., 1997: Mg II core-to-wing index: Comparison of SBUV and SOLSTICE time series, J. Geophys. Res. 102, 2597-2610.

Floyd, L.E., et al., 1998: Solar cycle 22 UV spectral irradiance variability, Sol. Phys. 177, 79-87.

Snow, M., McClintock, W., Woods, T., White, O., Harder, J., and Rottman, G., The Mg II Index from SORCE, Solar Physics, 230, 325-344, 2005.

Snow, M., M. Weber, J. Machol, R. Viereck, and E. Richard, Comparison of Magnesium II core-to-wing ratio observations during solar minimum 23/24, J. Space Weather Space Clim., 4, A04, doi:10.1051/swsc/2014001, 2014.

Viereck, R.A., and L.C. Puga, 1999: The NOAA Mg II core-to-wing solar index: Construction of a 20-year time series of chromospheric variability from multiple satellites, J. Geophys. Res. 104, 9995-10005.

Viereck, R., L. Puga, D. McMullin, D. Judge, M. Weber, W.K. Tobiska, The Mg II Index: A Proxy for Solar EUV, Geophys. Res. Lett. 28, 1343-1346, 2001.

Viereck, R. A., L. E. Floyd, P. C. Crane, T. N. Woods, B. G. Knapp, G. Rottman, M. Weber, L. C. Puga, and M. T. DeLand, A composite Mg II index spanning from 1978 to 2003, Space Weather, 2, S10005, doi:10.1029/2004SW000084, 2004.

Weber, M., J.P. Burrows, and R.P. Cebula, 1998: GOME Solar UV/VIS Irradiance Measurements between 1995 and 1997 - First Results on Proxy Solar Activity Studies, Sol. Phys. 177, 63-77.

Weber, M., 1999: Solar activity during solar cycle 23 monitored by GOME, Proc. European Symposium on Atmospheric Measurements from Space (ESAMS'99), ESTEC, Noordwijk, The Netherlands, 18-22 January 1999, WPP-161, European Space Agency, p. 611-616 (PDF 431kbytes, PS gzipped 186kbytes).

written by Mark Weber
last change: 2014/12/15
Institute of Environmental Physics, University of Bremen