Season Lag From Solar Angle
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?
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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Update: June 2012