Solar Radiation model - Diffuse Model Type

Discussion created by todd93 on Oct 22, 2013
Latest reply on Nov 21, 2013 by SWalbridge-esristaff
I am exploring the parameters that control the amount of diffuse radiation in the Solar Radiation tools, specifically, the "diffuse model type" and "diffuse_proportion".

The attached charts show comparisons between different values for these parameters. The top chart shows the diffuse radiation with diffuse_proportion set to 0.3 and 0.5. The results show what I would expect with more diffuse radiation with a value of 0.5.

However, the bottom chart that shows the comparison between the two different diffuse model types (Overcast vs. Uniform Sky) does not seem to make sense. For all sites, it shows the Overcast model giving more diffuse radiation than the Uniform Sky model. This difference is even more pronounced at sites near ridgelines.

Why would an overcast sky produce more diffuse radiation near the ridgeline than in a valley bottom?