On Jul 12, 12:00*pm, Graham P Davis wrote:
Will Hand wrote:
Why is the 564DAM line persistently a bit further north than it should be
then?
Or is it? GW could easily be responsible, if the Tropics are warming then
warmer, moister air is going to end up further north, is it not?

Sorry, I agree that the 564 line being further north - and all the others
too - is down to GW but not that the 564 line being further north is
responsible for the jet being further south. I think that reduced N-S
temperature contrast, because of the increase Arctic warming relative to the
tropics would lead to weaker jets and, presumably, they'd be further north.

Certainly, warmer, moister air due to GW will lead to heavier outbreaks of
rain when they occur. Deeper troposphere will also, I would have thought,
lead to more violent storms. How often we get these is something I wouldn't
like to guess - I'll leave it to the climate models.

--
Graham P Davis, Bracknell, Berks., UK. *E-mail: newsman not newsboy
"I wear the cheese. It does not wear me."


In case there is anyone else, like me, who does not understand the
significance of the 564 DAM, I found the following on the Met Office
web site:

Thickness lines
Pressure decreases with altitude, and thickness measures the
difference in height between two standard pressure levels in the
atmosphere. It is proportional to the mean temperature of this layer
of air, so is a useful way of describing the temperature of an
airmass.

Weather charts commonly show contour lines of 1,000-500 hPa thickness,
which represent the depth (in decametres, where 1 dam = 10 m) of the
layer between the 1,000 hPa and 500 hPa pressure levels. Cold, polar
air has low thickness, and values of 528 dam or less frequently bring
snow to the UK. Conversely, warm, tropical air has high thickness, and
values in excess of 564 dam across the UK often indicate a heatwave.
http://www.metoffice.gov.uk/weather/uk/guide/key.html

Graham,

What you are saying makes more sense to me. The cold pool of surface
water in the North Atlantic seems to be flowing out from Baffin Bay.
My idea is that it is melting Arctic sea ice and/or melting ice bergs
from a fast retreating Greenland ice sheet. Melting ice would explain
why the cold water remains on the surface rather than sinking. It is
fresh water and so does not the higher density of saline sea water.
OTOH why don't we see it coming down from the east of Greenland.

I suspect that the features we see in Western Europe at present and
blame on global warming are caused by the melting Arctic sea ice. When
that is completely melted, there will be a new regime much like that
dreamed of by Will.

Cheers, Alastair.

Cheers, Alastair.