Jahresbericht 08 - PMOD/WRC
Jahresbericht 08 - PMOD/WRC
Jahresbericht 08 - PMOD/WRC
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Reconstructing the Long Term Spectral Solar Irradiance<br />
Micha Schöll and Werner Schmutz<br />
We present a spectral reconstruction of solar irradiance<br />
back to 1610 utilizing sunspots for short-term<br />
variations and the open magnetic flux for long-term<br />
trend.<br />
Solar irradiance variation is an important forcing component<br />
in climate models as it is known that climate reacts to<br />
changing solar irradiance. As Rozanov et al. (2002) have<br />
shown, the Lyman-α line is of particular importance to<br />
chemical reactions in the upper atmosphere.<br />
To reconstruct past climate, spectra as a function of time<br />
are required. Following the approach of Krivova et al. (2005)<br />
the spectral reconstruction is based on a four component<br />
model with filling factors for the area of quiet sun, sunspots,<br />
faculae and network regions. Wenzler extracts the filling<br />
factors using MDI magnetogram data and images of the<br />
visible sun.<br />
Utilizing the open magnetic flux to reconstruct the longterm<br />
network evolution we obtain spectral irradiance back<br />
to 1610 where the Maunder minimum is below the current<br />
minimum.<br />
The sunspot area and faculae are reconstructed using the<br />
sunspot number. The long-term network is split into active<br />
and passive networks. The active network corresponds to<br />
the active areas on the sun and is hence reconstructed<br />
using the sunspot number. The quiet network is assumed<br />
to correspond to the open magnetic flux with the assumptions<br />
that no open magnetic flux translates to a quiet sun<br />
and that the current quiet network is 14 % in accordance<br />
with Foukal et al. (1991). Using this approach, together with<br />
the active area expansion (see Schöll and Schmutz 2007)<br />
and a modeled spectrum using the COSI code, we obtain<br />
the reconstructed spectrum, with the Lyman-α line (121.5<br />
nm) shown in Figure 1 and 2. Figure 1 is an enlargement of<br />
Figure 2 for the 1992 to 2001 period.<br />
References: Haberreiter M., Krivova N.A., Schmutz W., Wenzler T.,<br />
Reconstruction of the solar UV irradiance back to 1974,<br />
Advances of Space Research 35, 365-369, 2005.<br />
Foukal P., Harvey K., Hill F., Do changes in the photospheric<br />
magnetic network cause the 11 year variation of<br />
total solar irradiance?, ApJ 383, L89-92, 1991.<br />
Krivova N.A., Solanki S.K., Modelling of irradiance<br />
variations through atmosphere models. In: Memorie<br />
della Societa Astronomica Italiana Vol. 76, p. 834, 2005<br />
Schöll M., Schmutz W., Reconstructing the Spectral<br />
Solar Irradiance: The Active Area Expansion.<br />
In: <strong>PMOD</strong>/<strong>WRC</strong> 2007 Annual Report, p. 28, 20<strong>08</strong>.<br />
Rozanov E., Egorova T., Fröhlich C., Haberreiter M.,<br />
Peter T., Schmutz W., Estimation of the ozone and<br />
temperature sensitivity to the variation of spectral solar<br />
flux, In: From Solar Min to Max: Half a Solar Cycle with<br />
SOHO, ESA SP-5<strong>08</strong>, 181-184, 2002.<br />
Irradiance (mW/m 2 /nm)<br />
Figure 1. Reconstructed Lyman-α compared to SOLSTICE. The solid<br />
black line uses the reconstructed filling factors for all regions, while the<br />
dashed line displays the reconstruction using Wenzler’s MDI data and reconstructed<br />
network regions.<br />
Irradiance (mW/m 2 /nm)<br />
10<br />
9<br />
8<br />
7<br />
6<br />
1992 1994 1996 1998<br />
Time (Year AD)<br />
2000<br />
10<br />
9<br />
8<br />
7<br />
6<br />
5<br />
SOLSTICE<br />
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SOLSTICE<br />
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1700 1800 1900 2000<br />
Time (Year AD)<br />
Figure 2. Reconstructed Lyman-α from 1610 to the present using the<br />
open magnetic flux for the long-term trend network.<br />
29