"JPG" wrote in message
ups.com...
Will Hand wrote:

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This posting expresses the personal view and opinions of the author.
Something which everyone on this planet should be able to do.
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Air close to the surface will become very cold as it stagnates
due to radiation balance at this time of year so 850 hPa temperatures of -5
to -10 deg C are easily attainable.

A technical query - I thought 850 hPa is a useful level as it is free
from immediate boundary layer effects, such as radiative cooling, and a
lot of the relatively high 850 hPa temps shown on the models are due to
adiabatic warming through anticyclonic subsidence. Typically how long
does it take for radiative cooling effects to transfer to 850 hPa in
light wind clear-sky situations at our latitude in mid-winter, and how
much is indirectly due to land surface radiation and how much directly
due to radiation from the atmosphere itself?

Martin


Martin, no straight answers as it part depends on moisture, but in a typical
profile it is of the order of days. Land surface radiation I think dominates,
especially from snow covered surfaces, but again moisture and cloud complicate
the issue. However, at this time of year the short wave input is low or nil
depending on latitude and this is what is important.

Will.
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