On Wednesday, 23 September 2015 19:38:41 UTC+1, Graham P Davis wrote:



'In the northern hemisphere, the maximum temperature occurs near the
end of the third week of July and the minimum near the third week of
January. These are only a few days from the mid-point of the
meteorological seasons.'

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I am not sure this statement is true in general for the N Hemisphere.

For example, Helsinki has on average its lowest temperatures in
February. Even more so the further north you go.

http://www.worldclimate.com/cgi-bin/...24+1102+02974W



Those dates are correct (within plus or minus 5 days) as an average of
stations in the northern hemisphere which have at least one month per
year with a mean temperature near or below 0C. How do I know that?
Because it's those stations that I used when working out those dates
fifty years ago. Unless global warming has somehow added a delay
factor, I think they should still hold true. ;-)

The reason for +/-5 days is that the dates had to coincide with the last
day of ten-day periods beginning on 1st January. This means that the
date for July should have been the 19th and not the 20th. The reason
for calculating these dates was that we needed fixed dates for the
start of the positive degree-day season after mid-winter and the same
for the negative degree-day season after mid-summer.

--
Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer]
http://www.scarlet-jade.com/
I wear the cheese. It does not wear me.
Posted with Claws: http://www.claws-mail.org/
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That is the trouble with averaging over a number of locations.
The variability is lost.

'at least one month per year with a mean temperature near or below 0C.'
How near is near? Not that near surely as it would rule out a lot of stations south of 55N .

I contacted the Finnish Met Institute and the average date for the minimum temperature in Helsinki is 12th Feb.

Len
Wembury

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