Shown here are simulation of 1D and 3D solar radiation and the resulting surface irradiances. The cloud fields stem from a convective, shallow cumulus simulation and radiation has been recomputed using the MonteCarlo model MYSTIC from the libRadtran software package. The respective cloud fields have cloud fractions ranging from zero to 80%. When recomputing the radiative transfer for all the timesteps, the solar zenith angle is kept constant. Once computed with sza=40deg and once with sza=60deg.

The 1D radiation panel clearly shows the two differing solar zenith angles. Furthermore there is a strong correlation between sun shadowing and diffuse radiation.

The interesting part here is the occurrence of high direct and diffuse irradiances at the same spots. This is only possible because a sideways displacement of cloud shadows or diffuse radiation being scattered into regions where solar radiation hits unobstructed.