Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Night Warmth
Name: Nick Pryor
Status: student
Age:  15
Location: N/A
Country: N/A
Date: 2000-2001


Question:
Why does it stay warm at night? If it is sunny during the day the earth absorbs a substantial amount of the incident sunlight, unless the groun is snow covered. That energy re-radiates during the night, tending to keep the air warm. The effect is greatest if it gets cloudy at night because the heat radiation [infrared] tends to be trapped by the clouds.

Vince Calder


Nick,

Your question is very general -- the answer might depend upon where you live. It doesn't stay warm everywhere at night. Do you think it stays warm at night in the Antarctica?

I shall attempt a general answer: During the day, the earth and objects on it may be warmed by sunlight. The heat that is absorbed enables the earth and those objects to serve as a heat sources at night when there is no sunlight. Gradually, things cool off toward morning at which time the warming cycle begins again.

It is a little like a car engine that is cold when it is first started, warms while it is running, and cools again when it is turned off. Objects that are warmed during the day, gradually cool during the night. This is very apparent when one considers the difference in temperature between cities that are large sources of heat and the open countryside that cools much more quickly during the night.

Regards,
ProfHoff


Nick,

If you have ever removed a pot from the stove, you know it does not cool instantly but instead takes a bit of time to return to a lower temperature, safe for handling.

The heating caused by light from the sun occurs as the light strikes the earth and warms it. The warmth is highest closest to the earth and dissipates the further from the earth you move. Note that even though the sun is not "out" at night, the temperature, like the pan taken from the stove, remains elevated.

Additional continued warming could be provided by movement of air currents from warmer areas of the globe into cooler areas. In this case, the heating again originated from the sun, but the heat itself is carried in by adjacent warm air masses.

Both these mechanisms prevent the air temperature from dropping to the cold temperatures found in the expanse of space between the planets. Good thing that the sun rises each day to again create and continue the warming cycle.

Thanks for using NEWTON!

Ric Rupnik


Nick,

There are at least four reasons that it may stay warm at night.

If it is cloudy, the clouds present a barrier to the loss of energy from the air below them. Much of the energy (long wave radiation) lost from the surface is absorbed by the clouds and then re-radiated back into the air by the clouds, thereby reducing the decrease of temperature at night.

Secondly, warmer air may be coming into the area from the south (where it is usually warmer than in the north); this is called advection.

Third, a strong wind creates mechanical turbulence that mixes air from greater heights (where it is usually warmer at night when there are no or thin clouds) down to the surface, which, in the process, keeps temperatures at the surface warmer.

Fourth, it may be very humid, and I mean this in the absolute sense, such as on a very muggy day in the summer. Long wave radiation is absorbed by water vapor and thereby keeps the air warmer.

Sometimes, most or all of these conditions exist at the same time. In that case, nighttime temperatures are not much cooler than daytime temperatures.

David R. Cook
Atmospheric Section
Environmental Research Division
Argonne National Laboratory


Click here to return to the Weather Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory