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Hi Patricia & All, Feb 9, 2007
Both of these explanations miss the mark to some degree (no pun
intended) by placing emphasis on secondary effects while neglecting
primary cause.
The cooling or warming trend in any context; diurnal, regional or
seasonal, is determined by energy balance. In any context, cooling (a
passive process) continues UNTIL rate of energy gain exceeds rate of
energy loss. Or, if you wish, warming starts WHEN rate of energy gain
exceeds rate of energy loss.
Radiative cooling takes place year round and round the clock. Energy
comes in via sunlight, clearly not at night and clearly with less
intensity where it hits the earth at greater slope (even the word
climate is derived from slope).
In the diurnal context, warming continues well after noon because
incoming radiation, although decreasing, is greater than outgoing until
2:00 to 3:00 p.m. Once outgoing exceeds incoming, cooling will have
started. And so on....
Yours truly, Dave Webster, Kentville
Patricia L. Chalmers wrote:
> Hi there,
>
> I have always found this an interesting question too. Wayne's
> answer is on the right track, but implies that this is a coastal
> phenomenon. A very good explanation for why it is generally true that
> the coldest days of winter occur well after the days begin to lengthen
> was published in Colombo's Canadian Global Almanac, 1997. I obtained
> permission from the publishers to reprint it in the Halifax Field
> Naturalist in 1998. They told me at the time that it written by David
> Phillips of Environment Canada, the well-known weather expert. I
> still had it in my computer files, so I have pasted it in below.
>
> Cheers,
>
> Patricia L. Chalmers
> in Halifax (but a Winnipeg native, who is enjoying these brisk
> sunny days. If only we had some snow!)
>
> _________________________________________________________________
> Why isn't the shortest day of the year the coldest day of winter?
>
> There are at least three good reasons why the shortest day of
> the year, which falls on December 21st, isn't usually the coldest.
> First, the ground and particularly water bodies absorb and hold heat,
> in much the same way barbecue coals retain heat long after the
> barbecue is extinguished. It requires many weeks of cold weather
> before that stored heat is lost.
> Secondly, regions in the far north of Canada receive no direct
> heat from the sun until early February. As a result, pools of arctic
> air that accumulate over the country get progressively colder until
> the north's long winter night is over. Thirdly, as the winter
> advances, the snow cover usually increases in depth. Snow is one of
> the best insulators in the world - it can stop the upward flow of heat
> from the earth below as readily as it can reflect the incoming heat
> from the sun back into the air. Accordingly, winds originating over
> snow and ice-covered terrain tend to be colder in January and February
> (when the snowfields have had a chance to get established) than they
> are in December.
> So that is why the coldest day of the year often occurs in
> early February, on average, a month and a half after the shortest day
> of the year.
>
> Colombo's Canadian Global
> Almanac , 1997
> _________________________________________________________________________________
>
> At 02:19 AM 08/02/2007 -0400, Wayne Neily wrote:
>
>> Hello Andy,
>>
>> The short answer is the proximity of the ocean, which retains heat
>> much better than the land, and results in the delay of the coldest
>> weather in the fall (and the arrival of warmer weather in the spring)
>> in areas with coastal climates.
>>
>> Likely someone will be able to give you a more complete answer and
>> perhaps some additional factors.
>>
>> Wayne Neily
>> Tremont, Nova Scotia
>>
>>
>> "In nature's infinite book of secrecy
>> A little I can read." - William Shakespeare, 1607.
>>
>>
>> From: "Andy Moir/Chris Callaghan" <andyandchris@ns.sympatico.ca>
>> Reply-To: naturens@chebucto.ns.ca
>> To: <NatureNS@chebucto.ns.ca>
>> Subject: Re: [NatureNS] The Depths of Winter
>> Date: Wed, 7 Feb 2007 17:38:49 -0400
>>
>> I am curious why the low point for temperatures would come in
>> February. I would have thought it would come when the days are
>> shortest, in late December. What other factors are at play,
>> other than length of day, that make late January and early
>> February the coldest part of the winter? Andy Moir Freeport (or
>> Freezeport, lately)
>>
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