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Name: Herb
Status: Other
Age: N/A
Location: MI
Country: United States
Date: December 22, 2005

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?


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


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)

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