Transcript 04 LS Lecture - Atmospheric circulation

22.3
Atmospheric
Circulation
WIND
• The atmosphere is a mixture of gases
• Wind is the movement of these gases
• Named for the direction they come from
• Gases move from areas of higher pressure
to areas of lower pressure
H
L
Pressure Centers and Winds
 Low pressure
centers are
also called
Cyclones
(counterclockwise*)
 High pressure
centers are
also called
Anticyclones
(clockwise*)
*Rotation direction in Northern
Hemisphere
Pressure Differences
• LOW Pressure
causes air to rise &
generally takes
water vapor up=
• Clouds and storms
• HIGH Pressure
causes air to sink
& generally keeps
moisture out of the Winds ALWAYS move
atmosphere=
from HIGH pressure
• Clear skies & nice areas to LOW pressure
areas!!!!!!!
weather
CONVECTION
Air is warmed at the
surface
Warm air rises
Air is cooler higher
in the troposphere
Cold air sinks
Local Winds
 Local winds are caused either by
topographic
effects (mountains and land)
OR
variations in
surface composition
(near water)
Land & Sea Breezes
Coastal Areas
During the day, land
heats up quicker than
the water
The heated air above
the land expands and
rises=LOW pressure
Colder air over the
water is denser=
HIGH pressure
Pushes into land= SEA
BREEZE
Land & Sea Breezes
Coastal Areas
• Land cools faster than
•
•
•
water
The air above the
water is warmer =
LOW pressure
Air above the land is
cooler= HIGH
pressure.
Making a…
LAND BREEZE
Land or Sea Breeze?
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm?chapter_no=visualization
Mountain & Valley Breezes
Valley Breeze
During the day,
the valley floor heats
up and air above it
does too
Warm air rises up
the mountain
Air cools as it goes
up in elevation &
clouds may form
Mountain & Valley Breezes
Mountain Breeze
After sunset the
pattern reverses
As slopes cool,
nearby air cools
and sinks down
the mountain.
Mountain & Valley Breezes
Global Winds!
Global Winds
 Unequal heating and cooling of the
atmosphere from continents and oceans
creates high and low air pressures
 Add in the rotation of the Earth and global
wind patterns emerge
Non-Rotating Earth Model
• On a hypothetical
non-rotating
planet with a
smooth surface of
either all land or all
water, two large
thermally
produced cells
would form.
Circulation on a Non-Rotating Earth
Air would
warm and rise
at the equator
and cool and
sink at the
poles.
Coriolis Effect
• Click on image to watch video
The Coriolis Effect
The Coriolis Effect describes the apparent
deflection of an object based on the
rotation of the Earth below it.
The Coriolis Effect
Objects appear to
deflect to the right in
the northern
hemisphere and to
the left in the
southern hemisphere
http://nsidc.org/cryosphere/arctic-meteorology/images/coriolis.gif
Rotating Earth Model
• When the effect of
rotation is added to
the global
circulation model,
the two-cell
convection system
breaks down into
many smaller
cells.
http://sparce.evac.ou.edu/q_and_a/images/bc07.gif
Rotating Earth Model
•These cells lead
to the formation
of the global
wind belts.
Circulation on a Rotating Earth
Wind Belts
WIND BELTS
 Trade winds


are two belts of
winds that blow
almost constantly
from easterly
directions
From 0o to 30o
latititude
Warm, moist,
rising air (low
pressure)
WIND BELTS
 Westerlies
are the
prevailing winds
that blow westto-east in the
middle latitudes
 From 30o to 60o
latititude
Wind Direction
• The
PREVAILING
WIND is the wind
that blows more often from
one direction than from
• In
theother.
United States, the
any
WESTERLIE
S consistently move
weather from west to east
across the continent.
WIND BELTS
 Polar
easterlies


winds that blow
from the polar
high toward the
subpolar low.
From 60o to 90o
latitudes.
Cold and dry air
masses
WIND-LESS BELTS
 Doldrums
converging trade
winds at the equator
(O latitude) creating
calm areas
 Horse latitudes
diverging westerlies
and trade winds
(easterlies) create
calm at approximately
30 latitude
The Jet Stream
• Jet streams form at boundaries
between convection cells;
• High speed winds
• Blow in upper troposphere and lower
stratosphere
Identify the Wind Belts
Click on the link below to see the wind belts in action and answer
some questions!
http://meted.ucar.edu/hurrican/strike/orig/htc5_1.htm
Global Winds Influenced
by Continents
• The only truly continuous pressure belt is the
subpolar low in the Southern Hemisphere.
• In the Northern Hemisphere, where land masses
break up the ocean surface, large seasonal
temperature differences disrupt the pressure
pattern.
Energy from Wind