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WP6 Scientific interaction with user communities

 

Key tasks and achievements:

1. Compilation of the SOLID composite based on observed SSI data as recommendation for the climate community

2. The SOLID composite is used as independent validation of the SSI forcing dataset recommended for CMIP6

3. Study of the Earth's atmosphere response of different SSI datasets

 

1. Compilation of the SOLID composite based on observed SSI data as recommendation for the climate community

Figure 1: Upper Panel: Change of the annual mean of SSI in different spectral bins from 2003 to 2008 with respect to the variation in TSI for the same time interval. Shown are the relative changes for SOLID (black), SATIRE-S (blue), NRLSSI1 and NRLSSI2 (dark and light green), and the SORCE composite (red). For better illustration, the first and second spectral bin, i.e. for 121–122 nm and 150–200 nm is multiplied by a factor of 100 and 10, respectively, additionally shown in partly transparent color. Lower panel: Same as upper panel, but for the annual means of 1989 and 1994, for which no SORCE data is available (from Schöll et al., 2016b). 

 

2. The SOLID composite is used as independent validation of the SSI forcing dataset recommended for CMIP6

The SOLID observational composite (Schöll et al., 2016b) is used as independent validation of the SSI dataset recommended for the CMIP6 climate model intercomparison. The SSI forcing dataset is described in detail by Matthes et al. (2016). As such the SSI composite produced by the SOLID project is extremely valuable for an independent view on SSI reconstruction models.   

 

3. Study of the Earth's atmosphere response of different SSI datasets

The SOLID composite is based on 20 instruments and one reference spectrum (due to the high uncertainty in the other available reference spectra). In addition to SSI observations, 6 solar proxies are also considered. While these proxies do not strictly correspond to SSI observations, they are known to properly repro-duce SSI variations in given bands, and for specific time scales. The 10.7cm radio flux (or F10.7 index), for example, has been widely used so far as a proxy for the EUV band, whereas the 30cm flux is better suited for reproducing the solar rotational variability at longer UV wave-lengths.

To demonstrate the effects of SOLID spectra on the atmospheric energy balance, we performed calculations with the high resolution model LibRadtran, which is a library of radiative transfer equation solvers widely used for UV and heating rate calculations.  LibRadtran was configured with the pseudo-spherical approximation of DISORT solver, which accounts for the sphericity of the atmosphere, running in a six-streams mode. Calculations pertain to a cloud- and aerosol-free tropical atmosphere (0.56N), the surface reflectivity is set to 0.1 and effects of Rayleigh scattering are enabled. The atmosphere is portioned into 80 layers extending from surface to 80 Km, but signals above 23 Km are only presented. The model output is daily averages of spectral heating rates from 120 nm to 700 nm in 1 nm spectral resolution on 15th of January, calculated according to the recommendations for the Radiation Intercomparison of the Chemistry-Climate Model Validation Activity (CCMVal). Calculations for SOLID for solar maximum (2003) and solar minimum (2008) conditions were compared to alternative spectra such as NRLSSI2, SAT-IRE-S and SORCE. Given we are interested on the direct effect in atmospheric heating, the ozone feedback is not considered and ozone mixing ratios are kept constant in all calculations.

Figure 2: Comparison of solar heating rate differences (K/day) between solar minimum (2008) and maximum (2003) for the SOLID composite, NRLSSI2, SATIRE-S and SORCE. Panel a) shows the inte- grated (120-700 nm) heating rate anomalies whereas panels b)-d) show the relative contribution (%) of the 200–300 nm, 300–400 nm and 400–500 nm spectral bands to the integral. Grey shading indicates the uncertainty of the SOLID composite.  

 

Figure 3: Panel a: Solar spectral heating rate anomalies (K/day/nm) between solar minimum (2008) and maximum (2003) for SOLID. Panels b–d: Differences in solar cycle spectral heating rate anomalies between SOLID and NRLSSI2, SATIRE-S and SORCE.

Besides pure radiative effects of the 11-yr solar cycle to the thermal budget of the atmosphere, the ozone feedback has been analyzed using a 2-D chemistry climate model, which provides a computationally efficient way to characterize atmospheric effects.

 

Figure 4: Solar cycle effects in temperature (left) and ozone (right) for NRLSSI2, CMIP6 and SOLID SSI forcing.

Figure 4 shows that the annual mean stratospheric temperature response to the 11-yr solar cycle does not depend critically on the selection of the SSI dataset. SOLID shows comparable anomalies to the NRLSSI2 and the suggested solar forcing for the CMIP6 intercomparison. In all cases, the simulated warming in the stratospause is less than 1 K. The SOLID SSI forcing, however, introduces a slightly weaker ozone response when compared to the NRLSSI2 and CMIP6. CMIP6 and NRLSSI2 simulates essentially the same ozone response, as expected given that the recommended forcing has been derived by blending the NRLSSI2 and SATIRE-S. The simulated ozone solar cycle signature in ozone between 2001 and 2008 for SOLID shows an increase of 1.6% at 3 hPa.

 

The following Deliverables will be provided within WP6:

D6.1) Review report of ongoing and past studies on the use of TSI and SSI [month 4]

D6.2) Report on results from the survey: Determination of the needs of climate and chem.-climate community [month 8] 

D6.3) Determination of the needs of the wider scientific atmospheric and photobiology communities: [month 10] 

D6.4) Recommended time series based on results from WP2, WP4, and WP5 for the user communities: [month 30]

 

References

  • Matthes, K., Funke, B., Barnard, L., Beer, J., Charbonneau, P., Clivard, M., Dudok de Wit, T., Haberreiter, M., Jackman, C. H., Kretzschmar, M. et al., CMIP6 Solar Forcing, in preparation for Geosci. Model Dev (2016).
  • Schöll, M., Dudok de Wit, T., Kretzschmar, M., Haberreiter, M., Making of a solar spectral irradiance data set: data and methods, Journal of Space Weather and Space Climate, in press, (2016a).