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

Answer 1

Heat flow into the atmosphere (Hin) is generally least during the early morning hours, just before and around sunrise. This is because the Earth's surface cools overnight by radiating heat away, resulting in a lower temperature in the early morning. As the sun rises, solar radiation begins to increase, leading to a gradual rise in temperature and, consequently, an increase in heat flow into the atmosphere throughout the day. Thus, the minimum heat flow into the atmosphere typically occurs when the surface temperature is at its lowest, which is usually before dawn.