Ask A Scientist© Weather Archive

name         Jack
status       student
age          13
Question -   Why is the coldest time of day right after the sunrises???
I would expect the sun to heat the earth and the coldest time of day be
before visible light hits the surface and the sky is still dark.

Jack-

The earth continuously radiates heat into space and receives heat from space.
The change in temperature is controlled by the balance between these 
two.  Even
as the sun begins to rise, the balance is tipped toward a loss of heat...
therefore temperature goes down.

Larry Krengel
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Jack,

Because the Sun is so low to the horizon at sunrise, most of the energy is 
absorbed by the distant atmosphere.  Meanwhile, for cloudless skies at 
least, energy from the Earth's surface continues to be lost to the 
atmosphere directly above.  Thus, the lowest temperature of the night can 
still occur after sunrise.

David Cook
meteorologist working at Argonne National Laboratory
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