I wasn't around when this topic was initially discussed (or else, I missed it), but anyway, I want to take a stab at the explanation... Not sure if I can do better than Clark, but since our perspectives are different, it might work.

Solar radiation maximizes at solar noon (forget about daylight savings time and the like) due to the sun being highest in the sky. There is a shorter pathlength (i.e. less chance for scattering) and the rays are more concentrated at the surface. Temperature lags radiation and maximizes around 3-4PM. This has to do with net radiation at the surface... if this is positive, which it is from right after sunrise until mid afternoon. During these times, temperature rises. When net radiation at the surface is negative, temperature falls. This is true during evening, night, and early morning (before the sun rises too high in the sky). So, at night, temperature decreases because more terrestrial radiation is leaving the Earth's surface than is being absorbed. The atmosphere still exhibits vertical mixing, even though no more radiation is being absorbed at the surface. The warm suface layer mixes convectively upward at night, being replaced by cooler air at the surface. The warming of the surface starts again the next morning when the net incoming radiation again becomes positive.

Does this help at all?