At what specific time of day is heat flow into the atmosphere (Hin) least?

Answer 1

Heat flow into the atmosphere (Hin) is typically least during the early morning hours, just before and around sunrise. This is primarily due to the fact that the ground and surface have lost heat during the night, and the incoming solar radiation has not yet begun to warm the surface significantly. As the sun rises, solar radiation increases, which leads to a rise in temperature and an increase in heat flow into the atmosphere. Thus, early morning is when Hin is at its minimum.