I have always heard that the coldest time of the day is when the sun just does break over the horizon. When I go hunting in the morning, it really does feel like it gets colder at that time. Is this true? If so, why?
Posted February 26, 2007
The reason for this is that the earth's surface continually emits longwave infrared radiation. During the day, it also receives incoming shortwave radiation from the sun. At night, outgoing energy exceeds incoming, causing temperatures to fall. This process typically continues until the sun rises and climbs high enough for incoming radiation to become stronger than the outgoing, so that temperatures begin to climb again. In addition, there can be an effect on calm, clear morning where a very shallow layer of especially cold air very near the ground is mixed to a few feet higher when the sun first begins to warm the surface, causing temperatures a few feet off the ground (where we are more likely to notice it and where "official" temperature readings are taken) causing an added dip in the temperature at that time.