Transcript Slides - UMD | Atmospheric and Oceanic Science

Discussion Review 4/4
Midterm questions?
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
Sea Level Pressure
(Summer)
Low pressure
systems form
over land in N.H
summer. Why?
ITCZ moved
northward. Why?
Sun is overhead
in NH, so zone
of maximum
surface heating
shits seasonally
Sea Level Pressure (Winter)
High
pressure
forms over
land in NH
ITCZ moves
southward
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
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.
water moves, it
bends slightly
to the right due
to the Coriolis
effect.
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
Key Terms
 Sea breeze
Ferrel cell
 Land breeze
Hadley cell
 Valley breeze
Trade winds
 Mountain Breeze
ITCZ
 Katabatic wind
Ekman Transport
 Chinook Wind
Upwelling
 Santa Ana Winds
ENSO
 Polar cell
El Niño
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