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# 6 g-considering clouds

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Parameterisations of cloud cover in simple radiation models. As used in the class of Hydrology at the University of Trento

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### 6 g-considering clouds

1. 1. Riccardo Rigon IlSole,F.Lelong,2008,ValdiSella Solar Radiation Considering Clouds
2. 2. R. Rigon Transmitted direct radiation at the surface before clouds correction Transmitted direct radiation at the surface after clouds correction Hydrologists (and not only them) treat the influence of clouds separately It is assumed that the effects of clouds is an attenuation of the transmitted solar radiation 2 Considering Clouds
3. 3. R. Rigon Correction coefficient for diffuse radiation Hydrologists (and not only them) treat the influence of clouds separately An analogous formulation holds for diffuse radiation: 3 Considering Clouds
4. 4. R. Rigon Measured total radiation at the ground station i Estimation of the reduction coefficients (decomposition model) These reduction coefficients can be determined when we have ground measurements of total radiation, diffuse plus direct: 4 Considering Clouds
5. 5. R. Rigon reduction coefficient for diffuse radiation Estimation of the reduction coefficients (decomposition model) These assumption that is often made is that, the diffuse solar radiation measured at the station is proportional to the total radiation: 5 Considering Clouds
6. 6. R. Rigon Estimation of the reduction coefficients (decomposition model) Therefore when substituting this diffuse radiation expression in the total radiation equation of previous slides, it results at stations: 6 Considering Clouds
7. 7. R. Rigon Estimation of the reduction coefficients (decomposition model) And, for the direct radiation, at stations: 7 Considering Clouds
8. 8. R. Rigon The key factor is the to determine the above coefficient, on which the procedure followed so far has moved all the unknown. Its estimation pass through various parameterizations: Among the most known: •Erbs et al., 1982 •Reindl et al. 1990 •Boland et al. 2001 please find the details in Formetta et al., 2012 8 Considering Clouds
9. 9. R. Rigon One more issue With the help of the parameterizations above, the correction facotrs are determined for the stations. Which are a few points in a rugged terrain. How do you solve the problem to transport it everywhere ? 9 Considering Clouds
10. 10. R. Rigon We need to use some interpolation technique Like Kriging* or the Inverse distance weighting method** which is not the matter of the present slides. * Goovaerts, 1997 **Shepard, 1968 10 Considering Clouds