The deficit begins just before sunset when emitted longwave radiation from the Earth's surface exceeds solar insolation and longwave radiation from the atmosphere. Hourly variations in surface temperature for a location at 45 degrees North latitude over a 24 hour period. The relative placement of the temperature profiles for the various dates correlates to the amount of net radiation available for daily surface absorption and heat generation. The more energy available, the higher up the Y-axis the profile is on the graph . For all dates, minimum temperature occurs at sunrise .
Temperature drops throughout the night because of two processes.
First, the Earth's radiation balance at the surface becomes negative after sunset . Thus, the surface of the Earth stops heating up as solar radiation is not being absorbed. Secondly, conduction and convection transport heat energy up into the atmosphere and the warm air that was at the surface is replaced by cooler air from above because of atmospheric mixing. Temperature begins rising as soon as the net radiation budget of the surface becomes positive. Temperature continues to rise from sunrise until sometime after solar noon.