On 12/04/18 19:58, Nick Gardner wrote:
On 11/04/2018 18:54, Norman Lynagh wrote:
Food for thought

Norman, I have been led to believe that the Gulf Stream/North Atlantic
Drift is wind driven?

I have attended many lectures and a few conferences that have stated to
the above. Which is right?


I think the answer is yes and no. The circulation is partially
wind-driven; an explanation given fifty-odd years ago for any sudden
switch-off of the NAD in the past was a weakening of the subtropical
high, although the author was clutching at straws to explain this
bi-stable nature of the circulation.

The Gulf Stream is mainly a density current. Along the eastern seaboard
of the USA, the warm water of the Gulf Stream is of a lower density to
the cold, inshore water fed by the Labrador Current. The surface of the
warm water is higher than the cold and water flows from high water level
to low. As happens when air flows from surface high pressure to low, the
Coriolis effect results in the water flowing roughly parallel to the SST
isotherms.

Although the NAD has disappeared in the past at times, any talk of the
Gulf Stream itself shutting down can be dismissed; I reckon it would
take the Earth to stop spinning for that to happen. In any case,
evidence from Sargassum weed shows that the clockwise circulation of
warm water has continued for at least 30,000 years.

--
Graham P Davis, Bracknell, Berks. Web-site: http://www.scarlet-jade.com/
"There is nothing more frustrating than playing hide and seek with a
deaf wolf." [Benton Fraser]
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