Advection of Wind Reason for Europe's Relatively Mild Temperatures, Not Ocean Currents
Is the transport of heat northward by the Gulf Stream and North Atlantic
Drift, and its subsequent release into the midlatitude westerlies, the
reason why Europe�s winters are so much milder than those of eastern
North America and other places at the same latitude? Here, it is shown
that the principal cause of this temperature difference is advection by
the mean winds. South-westerlies bring warm maritime air into Europe and
northwesterlies bring frigid continental air into north-eastern North
Further, analysis of the ocean surface heat budget shows that the
majority of the heat released during winter from the ocean to the
atmosphere is accounted for by the seasonal release of heat previously
absorbed and not by ocean heat-flux convergence. Therefore, the existence
of the winter temperature contrast between western Europe and eastern
North America does not require a dynamical ocean.
Two experiments with an atmospheric general-circulation model coupled to
an ocean mixed layer confirm this conclusion. The difference in winter
temperatures across the North Atlantic, and the difference between
western Europe and western North America, is essentially the same in
these models whether or not the movement of heat by the ocean is
accounted for. In an additional experiment with no mountains, the flow
across the ocean is more zonal, western Europe is cooled, the trough east
of the Rockies is weakened and the cold of north-eastern North America is
In all experiments the west coast of Europe is warmer than the west coast
of North America at the same latitude whether or not ocean heat transport
is accounted for. In summary the deviations from zonal symmetry of winter
temperatures in the northern hemisphere are fundamentally caused by the
atmospheric circulation interacting with the oceanic mixed layer.
In the current paper we demonstrate that transport of heat by the ocean
has little in� uence on the contrast between the mild winters of western
Europe south of 60�N
and the harsh ones of eastern North America. North of 60�N the OHT
about a quarter of the contrast by restricting winter sea-ice cover.
The dominant cause of the contrast, at both latitudes, is atmospheric
advection around the Icelandic Low and the simple maritime�continental
climate distinction. The exact positioning and strength of the Icelandic
Low is important to the climate contrast and is shown to be greatly
influenced by the orographic forcing of the Rocky Mountains.
Therefore, the difference in the winter climates arises fundamentally
atmospheric processes and the seasonal storage and release of heat by the
ocean mixed layer. This is also all that is required to establish the
difference in winter climates between the west coast of Europe and the
west coast of North America at the same latitudes.
KEYWORDS: European winters
--------- Forwarded message ----------
Date: Wed, 3 Mar 2004 22:27:15 -0600
Subject: [P&C] Advection of Wind Reason for Europe's Relatively Mild
Temperatures, Not Ocean Currents
Is the Gulf Stream responsible for Europe�s mild winters?
By R. SEAGER1�, D. S. BATTISTI2, J. YIN2, N. GORDON1, N. NAIK1, A. C.
CLEMENT3 and M. A. CANE1
1Lamont Doherty Earth Observatory of Columbia University, USA
2University of Washington, USA
3Rosenstiel School of Marine and Atmospheric Sciences, USA
(Received 23 July 2001; revised 19 April 2002)
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