Why is sunrise the coldest part of day

Popular lore states that generally the lowest temperature of any given day occurs an hour after sunrise, because it takes some time for the heat from the Sun to reach Earth. But, it only takes about 8 minutes for the energy from the Sun to reach Earth. Is there something more complex going on that causes the Earth to take longer to heat up, or is this claim false?

The air and the ground get colder when no sun shines on them and hotter when the sun does. What we measure when we say it's colder is actually the air temperature. The sun's radiation has no effect on thermometers. As you can see in the graph, minimum temperature occurs about 30 minutes to 1 hour after sunrise hard to be exact with the ticks used. 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. After this time, mixing of the Earth's surface by convection causes the surface to cool despite the positive addition of radiation and heat energy. The above is a schematic of the typical diurnal cycle of surface temperature red and the net energy rate due to incoming solar black and outgoing longwave radiation blue.

Department of Commerce DOC. All Rights Reserved. My weather station says yes, remember cold air falls and without the ground being warmed there is nothing to push the cold air away. As I understand it, the suddenness you refer to is likely a combination of the steady decrease in air temperature until the ground has warmed enough to start heating the air instead of cooling it, as explained above, with wind chill associated with the air pushing eastward along the ground to replace air which has already been warmed, and is therefore lighter and rising.

Sign up to join this community. Give Now ». Noon Edition. Home Archives About Contact. Media Player Error Update your browser or Flash plugin. However, when the sun first rises it doesn't get warmer right away, but actually feels colder. In fact, barring any storm fronts, the coldest time of day is sometime just after dawn. H ands up if you don't like getting out of bed before sunrise?

For many of us the rapidly lengthening nights at this time of year force a pre-dawn rise, though the changing clocks later this week may give us a short respite. One reason for wanting to stay under the duvet is because it feels so cold at this hour, but is it really the coldest time of day?

There is something about the sight of those first rays of light that give a feeling of warmth, but it is an illusion.

In fact the mercury is usually still falling, and the coldest point in the day is shortly after daybreak.