Transcript Wind and the Ocean - Bowie Aquatic Science

Wind and the Ocean
Wind
• Currents of air
• Develop when two adjacent bodies of air have
different densities.
• Denser air sinks, pushing less dense air upward.
• Convection current is produced.
• Density of air is affected by temperature and
water vapor.
• Water vapor in an air mass decreases its density
because water vapor is about half as dense as
air.
Air Pressure
• Force of the air mass on earth
• High pressure: dry, dense air
• Low pressure: moist, less dense air.
Ocean Wind
• Sea breeze: cooler, denser air above the ocean
or lake sweeps over the shore as air warmed by
the land rises.
-beach areas are usually cooler in the summer
than inland
• Land breeze: at night, breezes blow off land as
the warmer air over the ocean rises.
• Ocean winds tend to keep nearby coastal lands
relatively warm in the winter and cool in the
summer.
Global Winds
• Heat is not distributed evenly on the earth.
• The equator receives about 60 times more
sunlight than the poles.
• Hot (and usually humid) equatorial air
masses are less dense
• Cold (and usually dry) polar air is more
dense.
Global Winds cont.
• At the poles cold, dense air sinks then
flows toward the equator.
• Polar air warms as it moves toward the
equator,
• At the equator, hot, moist and less dense
air rises and moves toward the poles.
• Equatorial air cools as it moves toward the
poles.
• Convection cells are formed.
Earth’s Rotation and the Effect on
Wind
• Rotates from west to east
• Spherical so therefore the equator rotates faster than the
poles
• Cold air from the north pole can’t keep up with the land
beneath it
• Polar easterlies: blowing from the northeast from poles
to 60° N.
• Trade winds: blowing from the northeast from 30°N to
equator.
• Prevailing westerlies: blowing from the southwest from
30°N to 60°N (dominant winds in US)
Global Wind Patterns
Winds cont.
• Doldrums: light shifty winds at the equator
(named for lack of wind)
• Horse latitudes: light variable winds at
30°N
Winds and Surface Currents
• Winds can produce currents if they blow from
the same direction for long periods.
• When wind pushes constantly on the ocean
surface, water particles at the surface begin to
move but not in the direction of the wind.
• The rotation of the earth causes water to form a
current at a 90° angle to the wind (Ekman
spiral).
• Currents will move right in the northern
hemisphere and left in the southern hemisphere.
Gyres
• Circular current
• Formed by a combination of prevailing winds,
the rotation of the Earth, and land masses that
interfere with the movements of water currents.
• Due to the Coriolis Effect they rotate clockwise
in the northern hemisphere and
counterclockwise in the southern hemisphere.
• Important because they move the drifting
plankton thousands of km across the ocean.
Main Ocean Gyres