On Thu, 24 Sep 2015 15:50:29 -0700 (PDT)
Len Wood wrote:
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.'
------------------------------------------------------------------------
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.
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 .
As the purpose in producing the figures was related to the production of
maps of Arctic Ice conditions, stations in areas unaffected by sea-ice
were largely irrelevant.
Yes, variability was lost and that was entirely necessary for the
purpose in hand. However, in working out the overall mean minimum and
maximum dates, I did notice something rather strange in the western
Russian Arctic. In that area, the stations showed a double minimum. I
suspect that may have been due to the short-period normals - some
only 10 years - that I had to use for several stations in the area,
--
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/