LETTERS TO THE EDITORS
Winds of Change
To the Editors:
Richard Seager's exposé of the myth about the Gulf Stream
warming England ("The Source of Europe's Mild Climate,"
July-August) is most welcome. Some 50 years ago when I was a summer
student employee at the Woods Hole Oceanographic Institution, a
kindly meteorologist told me about continental and maritime
climates, and how the Gulf Stream had little to do with making the
air that blows across Britain in winter warmer and damper than when
it left Canada. It seems remarkable that many people—even some
professional oceanographers—have still not understood this.
I would add to what Dr. Seager wrote that the Gulf Stream is not a
warm river flowing through a cold ocean. On the contrary, it is the
boundary between warm water to its east and south (more or less) and
cold water to its west and north. East of longitude 60°W, its
surface temperature is not even slightly greater than that of the
water on its right flank. To be sure, the sea-surface temperature in
the northeastern North Atlantic is several degrees higher than at
similar latitudes in the North Pacific, but that is a consequence of
the regional wind field.
Moreover, such language as "heat transported by the Gulf
Stream" is incoherent. "Heat" is a mode of energy
transfer, like work, not a substance or other seawater property that
is transported by a current. The language gropes for the concept of
internal-energy transport. But thermodynamics establishes even
internal energy only as differences in values between different sets
of state variables. So a calculation of internal-energy transport is
logically and physically meaningless unless the corresponding mass
transport is zero, as, for example, through a section spanning the
Atlantic, surface to bottom. These ocean-wide budgetary calculations
say nothing about causality, however, and they are somewhat distant
from the immediate air-sea exchanges that modify the mid-latitude westerlies.
Bruce A. Warren
Woods Hole Oceanographic Institution
Woods
Hole, MA