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 Season Lag From Solar Angle
Name: Herb
Status: Other
Age: N/A
Location: MI
Country: United States
Date: December 22, 2005


Question:
If December 21st (or there abouts) is the shortest day in the Northern Hemisphere, why is it not the coldest?
Why is it not the middle of winter rather than the beginning?



Replies:
Herb,

It takes the Earth a long time to cool off. Heat has to be released from a significant storage of energy in the ground, trees, buildings, etc. While the cooling is taking place, a lot of energy is still being released into the atmosphere, slowing the cooling. So, the coldest temperatures come later, after this cooling has occurred (in January or early February).

The reverse situation occurs in the Summer. June 21 is not the hottest day of the year in the Northern Hemisphere, as it takes the a long time for the ground, trees, buildings, etc. to warm up; the warmer they become as the Summer progresses, the more heat is released into the atmosphere, resulting in the hottest days being later (July and August).

David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory


Herb,

I am assuming that you were thinking that the Northern winter solstice should be correlated to temperature since, by definition, winter solstice is the day that that hemisphere is most inclined away from the sun. If the sun were the only factor in the average temperature of that day each year, then you would be correct. However, as you might suspect, there are other factors. One of them is the thermal inertia stored over the summer (through autumn) months. Conversely, one also finds that the summer solstice is not the hottest day, but rather the beginning of summer. Again, it is because of the relatively low heat from the previous months. It is rather like why it goes until August and September that one can finally swim in the Northern Atlantic beaches - it takes a while for the waters to heat up.

Greg (Roberto Gregorious)



Click here to return to the Environmental and Earth Science 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