Winds
Different areas of Earth receive different
amounts of the Sun’s radiation.
•
This unequal heating of the Earth causes differences in air
pressure.
 Warm, less dense air rises forming an area of low Pressure
 Cold, dense air sinks and creates an area of high pressure
• Wind is the movement of air molecules from an area
of high pressure to an area of lower pressure
• Warm (tropical) air rises and cold (polar air) sinks to
form patterns of wind called wind cells.
• Scientists use a model
that has 3 wind cells
• All three wind cells exist
on both sides of the
equator, in the northern
hemisphere and the
southern hemisphere.
The Coriolis Effect
The deflective effect of the
earth's rotation on all freemoving objects, including the
atmosphere and oceans.
Gaspard-Gustave de Coriolis, 1835
Coriolis Effect
(Northern
Hemisphere)
coriolis (n.hemisphere)
A plane flying from Anchorage, Alaska
directly toward Miami, Florida would miss its
target due to the Coriolis effect. The target
location where the plane was headed when it
took off has moved with Earth's rotation, so
the plane would end up to the right of its
original target.
Coriolis Effect
(Southern
Hemisphere)
coriolis (s. hemisphere)
A plane flying from Tierra del Fuego,
Argentina directly toward Rio de Janeiro,
Argentina would miss its target due to
the Coriolis effect. The target location
where the plane was headed when it
took off has moved with Earth's rotation,
so the plane would end up to the left of
its original target.
In reality, pilots take the Coriolis effect
into account so they do not miss their
targets
Global Winds
Patterns of air circulation caused by the combination of convection
currents (wind cells) and the Coriolis Effect.
Surface winds:
• Winds between pressure
zones are named for the
direction that they come
from.
• There are 3 main wind
systems.
Trade Winds
• Blow from 30˚ towards
the equator (East to
West)
• warm and steady in
both direction and
speed
• provided regular trade
routes for sailing
Prevailing Westerlies
• Blow west to east between 30˚ to 60˚lattitude in both
hemispheres; in the opposite direction of the trade winds.
Polar Easterlies
• Blow east to west between 60˚ to 90˚lattitude in both
hemispheres.
Near the equator, very little wind and daily rain patterns
called the doldrums
High Altitude Winds
• Jet Stream: narrow belt of air in the upper
troposphere which moves eastward at high speedusually in middle latitudes
• height range: 6,000-12,000 meters, speed: 150-300 knots
• dips account for cold polar air in US during winter
• related to strong thunderstorms in spring & summer
• used by planes to assist with eastbound flights
Jet streams move faster in the winter.
Moves storm systems across the country.
Local Winds
Winds that are caused by local geographic
features.
Land & Sea Breezes
• during day, land heats faster than water, and
generates a sea breeze: cool breeze blowing
from the ocean to replace the rising warm air
from land
• at night, land cools faster than water and
generates a land breeze (opposite of above)
Land Breeze
Sea Breeze
Mountain & Valley Breezes
Caused by
change in
Temperature
and elevation