Discussion Review 4/3
AOSC 200
Sarah Benish
Outline
 I. Local Wind Systems
 II. Global Winds
 III. Atmosphere-Ocean Interactions
I. Local Winds: Sea Breeze
As the surface warms, convection begins. The rising air “pushes” up the isobars,
creating a pressure gradient. As air over land expands, a low pressure system
forms at the surface and winds blow from ocean to land.
Land Breeze
Valley Breeze
Sun heats the valley walls,
which heats the surface
air. The heated air (being
less dense), rises as a
gentle upslope wind.
At night, the flow reverses
Mountain Breeze
Reverse of valley
breeze; happens at
night.
Cooler, more dense
air glides downslope
into valley.
Katabatic Winds
 Any downslope wind, but usually reserved for
downslope winds that are stronger than mountain
breezes.
Chinook Winds
 Warm, dry,
downslope wind
that descends on
the eastern slope
of the Rocky
Mountains
 Strong westerlies
aloft flow over a
north-south
trending
mountain range
 As the air descends, it is compressed
and warmed.
 Main source of warmth?
Compressional heating.
Santa Ana Winds
 A warm, dry wind that blows downhill from east or
northeast into southern California
 Source of heating? Compressional heating
 Cold, dense air from high deserts moves through
mountain passes. Warms as it descends into coastal
regions.
II. Global Winds
 Single Cell Model
 Assumptions:
 1. Surface is uniformly covered with water
 2. Sun is always directly over the equator
 3. Earth does not rotate
But this does not explain the mid-latitude westerlies!
 Three-Cell Model
 Allows the earth to spin
ITCZ
 Intertropical Convergence Zone
 Where the northeast trade winds meet with the
southeast trade winds
 Usually very wet since rising air develops into huge
thunderstorms that drop huge amounts of rain
III. Atmosphere-Ocean
Interactions
Ekman Transport
 Ocean water is moved by wind
 Also affected by Coriolis forces
Ekman Spiral
 Wind blows
parallel to the
coastline. As the
wind blows over
the ocean, the
surface water is
moved.
 As surface water
moves, it bends
slightly to the right
due to the Coriolis
effect.
 The water
As the surface water drifts away from the coast, cold, nutrient-rich
water from below rises (upwelling) to replace it.
Upwelling is the strongest and surface water is the coolest where
wind parallels the coast.
beneath the
surface also
moves, and it too
moves slightly to
its right.
El Niño
 Easterly trade winds weaken and warm water is transported
from the western Pacific to the Eastern Pacific.
 Southern Oscillation: seesaw pattern of reversing air
pressure at opposite ends of the Pacific Ocean.
 ENSO: basically simultaneous pressure reversals and ocean
warming.
 Global Weather?
 W. Pacific: Less rainfall as warm Pacific water moves east
 Shift in rain patterns moves subtropical jet stream from normal
path
 Change in path of sub-tropical jet allows El Niño to affect
weather in mid-latitudes
Key Terms
 Sea breeze
 Hadley cell
 Land breeze
 Trade winds
 Valley breeze
 ITCZ
 Mountain Breeze
 Ekman Transport
 Katabatic wind
 Upwelling
 Chinook Wind
 ENSO
 Santa Ana Winds
 El Niño
 Polar cell
Game
 First word: without saying
key words, walk around the
room describing your
concept until you find your
partner.
 Second word: With your
partner, play Pictionary with
your second words. Be sure
to label where high and low
pressure systems are, if
applicable.
 WORDS YOU CANNOT
SAY:
 Land
 Breeze
 Sea
 Wind
 Trade
 Cell
 Mountain
 Etc.