Gulf Stream
Q: What causes the Gulf Stream? --T.M., New York, NY
 A: The Sun causes the Gulf Steam and all other
global currents on Earth: wind and water. Light and
heat pour from the Sun and hit Earth more directly at
its equator than at its poles. Air at the equator,
therefore, gets hotter than at the poles.
This NASA image shows the Gulf Stream (light green) from its origin at the tip of
Florida to where it branches into two currents off the coast of Newfoundland.
(Courtesy of
NASA.)
Heat passes from warmer to cooler bodies. Hot
tropical air moves towards the poles in huge
convection currents that force cold polar air towards
the equator and cause winds. The winds drag across
vast areas of sea and pull the surface water in the
same direction, especially where waves increase the
friction between wind and water.
The Earth rotates from west to east and moves out
from under the atmosphere as the warm air moves
north and south towards the poles. This makes the pole-heading currents appear to curve to their
right in the Northern Hemisphere and to their left in the Southern.
In the Northern Hemisphere, great warm winds sweep up from the equator toward the pole, curve
to their right, move into a clockwise circular pattern over the Atlantic Ocean, and bring cool polar
air back to the equator. The winds drag the surface sea waters into a similar gyre.
The Gulf Stream is a part of this clockwise-rotating system of currents in the North Atlantic. A
river of seawater, called the North Equatorial Current, flows westward off the coast of northern
Africa towards the West.
Off the coast of South America, the North Equatorial Current forks into a two branches: one
passes into the Carribean, the other flows north and east of the West Indies. The two branches
rejoin and pour through the Straits of Florida at an incredible rate of 30 million cubic meters per
second to become the Gulf Stream. For comparison, the Mississippi, the Amazon and the sum of
all other rivers surging into the Atlantic amount to a meager 0.6 million cubic meters per second,
says Michael S. McCartney, Senior Scientist at the Woods Hole Oceanographic Institution.
A western boundary current, the Gulf Stream flows roughly parallel to the east coast of the
United States, picks up more water, and reaches about 80 million cubic meters per second at Cape
Hatteras, off the coast of North Carolina. An east-blowing wind separates the Gulf Stream from
the continental margin at Cape Hatteras. There the Gulf Stream twists into huge swirls and
meanders of warm water.
A part of the Gulf Stream forms a countercurrent that flows south and then west. The
countercurrent rejoins the Gulf Stream on its seaward side along the coast of Florida and the
Carolinas.
The main Gulf Stream current continues north, veers to the east, passes close to the Grand Banks,
south of Newfoundland, where it branches, says McCartney, into two currents: the North Atlantic
and the Azores Currents.
The North Atlantic turns north just east of Newfoundland, flows east toward the British Isles and
then north along Norway, warming the land as it goes. The west coast of Norway enjoys extra
warmth by a good 50 degrees Fahrenheit (10 degrees Centigrade) above average annual
temperature for its latitude.
The second branch of the Gulf Stream, the Azores Current, flows east past the Azores Islands
towards Portugal, then south, and finally heads back, west as the North Equatorial Current. This
closes the loop of the clockwise-going Atlantic gyre.
The sun causes the Gulf Stream by heating the Earth's equator more than its poles. The Gulf
Stream helps to redistribute the heat by carrying warm waters towards the North Pole.
Further Surfing:
USATODAY.com, Ocean weather, winds, waves, tides: the Gulf Stream,
NASA Earth Observatory.
Woods Hole Oceanographic Institution,
Woods Hole, Massachusetts. |
