OK, honest thermodynamics/atmospheric physics questions that has puzzled me for a long time. Right now my temp is 60.3 °. Temps are dropping very slowly. Sometimes on nights like tonight's the temps completely steady out. The ground is warm so it radiates energy at a high rate. To slow (or even stop) the temperature decrease, something must be adding energy, but what is it? The sky is clear so there is no downwelling radiation from clouds. There is no wind so there is no warm-air advection or turbulent mixing. Where is the energy coming from? Is it radiating from the water vapor in the air?