Download Global and Local Winds

Global
and Local Winds
Review of Air
Air Movement
Air Pressure
• Wind is the movement • Differences in air
of air caused by
differences in air
pressure
• The greater the
difference, the faster
the wind moves
pressure are caused
by the uneven
heating of Earth
• Uneven heating
produces pressure
belts which occur
every 30° latitude
Winds
• Differences in air pressure produce winds.
• Pressure difference between a high pressure
area and a low pressure area determines the
strength of the wind.
( larger pressure differences  stronger winds)
• Difference in air temperature also lead to
pressure differences that produce winds.
Pressure Belts
• AT EQUATOR
• As warm air rises at the equator and
moves toward the poles, it cools
• As it cools, some of the air sinks around
30° north and south of the equator
• AT POLES
• At the poles, cold air sinks and moves
towards the equator
• Around 60° north and south, the air
begins to heat up and rise
Coriolis Effect
• Once air has been set in motion by the pressure belts
•
it is deflected from its path by the Earth’s rotation.
This deflection is called the "Coriolis Force"
• In the northern hemisphere, air moving from high to
low pressure is deflected to the RIGHT.
Cyclonic wind pattern around L pressure area
• In the southern hemisphere, air moving from high to
low pressure is deflected to the LEFT.
Anticyclonic wind pattern around H- pressure
area
Coriolis Effect
Jet Stream
• The jet streams are
•
•
narrow belts of high
speed winds that blow
in the upper troposphere
and lower stratosphere
Jet stream is a narrow
ribbon of moving air
caused by temperature
differences between the
earth’s equator and the
poles.
Separates warm air
from cold air
The term "jet stream" is often used to
refer to the rivers of wind high in the
atmosphere - above about 20,000 feet
- that steer storms. They also help
determine locations of areas of high
and low air pressure at the Earth's
surface.
Jet Stream
• Narrow belts of strong wind • Jet streams form between areas of low pressure and
•
•
•
•
high pressure
Polar jet stream forms at the boundary of cold, dry
air to the north anf warmer, more moist air to the
south.
Jet streams move faster in the winter because of
differences between cold air and warm air is greater.
The JET STREAM moves storms across the
country.
Jet pilots take advantage of jet streams moving
east but fly at different altitudes moving west !
Global Winds
• Each hemisphere has three wind belts
• Each hemisphere contains three looping
patterns of air flow called convection cells
• Each of convection cells correlates to an area
of Earth’s surface , called a wind belt.
• These winds are called prevailing winds and
curve because of the Coriolis Effect.
Global Winds
• The combination of pressure belts and the
Coriolis Effect cause GLOBAL WINDS
• Some examples of global winds are polar
easterlies, westerlies, and trade winds
Remember!
Northern Hemisphere
deflects right.
Southern hemisphere
defects left.
Global Winds - Polar Easterlies
• Prevailing Winds that blow from east to west
• Wind belts that extend from the poles ( 90 )
to 60° latitude
• Formed from cold sinking air moving from the
poles creating cold temperatures
Global Winds - Westerlies
• Prevailing Winds
that blow from
west to east
• Wind belts found
between 30°
and 60° latitude
• Flow towards the
poles from west to
east carrying
moist air over the
United States
Global Winds - Trade Winds
• Prevailing Winds that blow from east to
west
• Winds that blow from 30° almost to the
equator
• Called the trade winds because of their
use by early sailors
Global Winds - Doldrums
• Trade wind systems of Northern and Southern
Hemisphere meet at the equator in a narrow
zone called the doldrums.
• Located along the equator where no winds
blow because the warm rising air creates an
area of low pressure.
• Surface winds are weak.
Global Winds - Horse Latitudes
• Sub-tropical high pressure zones
• Occur at about 30° north and south of the
equator where the winds are very weak
• Most deserts on the Earth are located here
because of the dry air
Global Winds
Local Winds
• On a scale much smaller that a global
scale; not part of global wind belts.
• Generally move short distances
( <100 km. )and can blow in any
direction
• Caused by geographic features that
produce temperature differences
• Called breezes.
Local Winds - Sea Breezes
• High pressure is created
•
over the ocean during the
day and low pressure over
land due to uneven
heating
Air moves from the ocean
to the land creating a sea
breeze
See a satellite animation at
http://atmo.tamu.edu/clas
s/atmo203/tut/seabr/sea1
8.html
Sea Breezes
• A sea breeze, is created during the day because
solar radiation warms the land more than the
water.
• Air over the land is heated by conduction.
• Heated air is less dense and has lower pressure.
• Cooler, denser air over the water has higher
pressure and flows toward the warmer, less
dense air.
• Convection current results and wind blows from
the sea toward the land.
Local Winds - Land Breezes
• Low pressure occurs
•
over the ocean during
the night and high
pressure over land due
to the uneven heating
of earth
This causes wind to
move from the land to
the ocean creating a
land breeze
Land Breezes
• At night, land cools much more quickly than
ocean water.
• Air over the land becomes cooler than air
over the ocean.
• Cooler, denser air above the land moves over
the water, as the warm air over the water
rises.
• Movements of air toward the water from the
land is called a land breeze.
Local Winds - Animation
• Go to
http://www.classzone.com/books/earth_science/terc/content/visuali
zations/es1903/es1903page01.cfm?chapter_no=visualization
and view the animation of land breeze and
sea breeze.
• Sketch the a land breeze and a sea
breeze in your notes.