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Redistribution of Solar Heat Energy
POLES
Chris Henze, NASA Ames, Public
Domain, http://people.nas.nasa.gov/
~chenze/fvGCM/frances_02.mpg
EQUATOR
Lecture 11: Wind 2, Current
Introduction to Oceanography
•  Convective heat transfer moderates Earth climate
•  Heated air expands & rises, then cools & sinks
Atmospheric water vapor map, April 10 May 10, 2017.
Data from http://www.ssec.wisc.edu/data/comp/wv/
Adapted from image at http://www.yourhome.gov.au/technical/images/62a.jpg, Public Domain?
Atmospheric Circulation Without Rotation
Cold, more dense air
sinks near the Poles
Background image
from Smári P.
McCarthy, Creative
Commons A S-A 3.0,
http://
commons.wikimedia.or
g/
wiki/File:Earth_equator
_northern
_hemisphere.png
Warm, less
dense air rises
near the
Equator
Cold, more dense air
sinks near the Poles
The Coriolis Effect
•  To an Earthbound observer (i.e., us):
•  Northern Hemisphere: Earth’s
rotation causes moving things to
curve to their right
Moving things: Air masses, oceanic flows,
missiles, anything with mass
•  Southern Hemisphere:
Earth’s rotation causes moving
things to curve to their left
National Snow and Ice Data Center, free
for educational use, http://nsidc.org/
arcticmet/factors/winds.html
The Coriolis Effect on Earth
•  Surface velocity
increases from pole to
equator
•  Points on the equator
must move faster than
points near the poles to
go around once a day
•  Latitude velocity
differences lead to
curving paths
–  Example: Merry-go
round
National Snow and Ice Data Center, free for educational
use, http://nsidc.org/arcticmet/factors/winds.html
But wait – why do storms
(including hurricanes and cyclones) go
backwards?
Northern Hemisphere: Hurricane Isabel (2003) NASA,
Public Domain, http://visibleearth.nasa.gov/view_rec.php?
id=5862
Southern Hemisphere: Cyclone Drena (1997)
NASA, Public Domain,
http://www.ngdc.noaa.gov/dmsp/hurricanes/
1997/drena.vis.gif (now moved)
Questions ?
1
Atmospheric Circulation including Coriolis
Actual
forecast of
surface winds
Pacific surface wind
forecast-hindcast, National
Weather Service
Environmental Modeling
Center/NOAA, Public
Domain, GIF by E. Schauble
using EZGif
Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html
–  Each cell: ~
30o
latitudinal width
•  Vertical Motions
0o
60o
–  Rising Air: and
Latitude
–  Sinking Air: 30o and 90o Latitude
•  Horizontal Motions
–  Zonal winds flow nearly along latitude lines
–  Zonal winds within each cell band
3 Cells per hemisphere:
Polar
Active (updraft on hot
side, downdraft on cold
side)
Ferrel
PO
LA
Y F
ER
RE
L
•  3 convection cells in each hemisphere
Atmospheric Circulation including
Coriolis R
HADLE
Atmospheric Circulation including Coriolis
Passive (downdraft on
hot side!)
Hadley
Active
•  DUE TO DEFLECTIONS BY CORIOLIS!
UCLA figure – background image unknown.
Atmospheric Circulation including
Coriolis
•  Latitudinal
winds:
–  0-30o: Trade
Winds
–  30-60o:
Westerlies
–  60-90o:
Polar
Easterlies
Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic,
http://en.wikipedia.org/wiki/File:AtmosphCirc2.png
Atmospheric Circulation including Coriolis
Cell Boundaries:
60o: Polar Front
Polar Front
Horse
Latitudes
30o: Horse
Latitudes
Doldrums
0o: Doldrums
Vertical air movement
(up at Polar Front
and Doldrums, down
at Horse Latitudes)
Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic,
http://en.wikipedia.org/wiki/File:AtmosphCirc2.png
2
Questions
Local Meteorology of Southern California
Marine layer against the Southern California mountains
Photo by Dr. Jonathan Alan Nourse, CalPoly Pomona,
http://geology.csupomona.edu/janourse/Storms,%20Floods,%20Landslides.htm
Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html
Sea Breeze
Mediterranean Climate
•  LA: Subtropical latitude, abutting ocean
•  Subsiding flow: sinking air
–  Clear most of the year
•  Effects of coast:
Land warms fastest
during the day. Air
expands and rises
Ocean surface
temperature changes
slowly. Air displaces less
dense rising air on land.
–  Higher humidity--- thermal buffer
•  Winter Storms
–  Pole-equator temp difference larger in winter
–  Speeds up jet stream, big storms get pushed our
way
Result – wind from sea towards land
Jesús Gómez Fernández, Wikimedia Commons, Creative Commons A S-A 3.0, http://commons.wikimedia.org/
wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.png
Land Breeze
Land cools fastest
at night. Air
contracts and sinks
Ocean surface
temperature changes
slowly. Air is pushed
away and up by cooler
denser land air.
Marine Layer
•  Cold waters, warm air: thin cloud layer
on ocean surface
–  Subtropics: H pressure, regional
subsidence
•  Cloud layer flows onto land at night
•  Evaporates over land by day
Result – wind from land towards sea
Adapted from Jesús Gómez Fernández, Wikimedia Commons, Creative Commons A S-A 3.0, http://
commons.wikimedia.org/wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.png
LAND
OCEAN
UCLA figure
3
UCLA Marine Layer
Santa Ana Winds
• 
• 
• 
• 
• 
Canada: Chinook
Colorado: Downslope Winds
Germany: Foehn Winds
France: The Mistral
Southern CA: Santa Ana Winds
Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA
Santa Ana Winds
NASA image, Public Domain, http://photojournal.jpl.nasa.gov/catalog/PIA03892
Santa Ana Winds
Winter: Canadian cold air
pushes down into
Southwestern US
High pressure pushes dry desert air
downslope, to sea
Compression of sinking air causes
heating
Heating lowers humidity
Wind Speeds: up to ~ 70mph ≈115
km/hr
Funneling effect through canyons
Feeds dangerous brush fires
Weaker in summer
~ 30 mph
Piotr Flatau, Wikimedia Commons, Public Domain,
http://en.wikipedia.org/wiki/File:Santa_ana_wind1.jpg
High Plateau
Adapted from N. Short Remote Sensing
Tutorial/NASA, Public Domain, http://
rst.gsfc.nasa.gov/Sect14/katabatic.jpg
~
San Gabriel/Bernardino Mtns.
0
50
km
Los
Angeles
Mojave Desert
Santa Ana Winds
Santa Ana Winds
Santa Ana Winds:
dry & warm,
Encourage
destructive fires
Fertilize ocean?
• 
• 
• 
• 
• 
Canada: Chinook
Colorado: Downslope Winds
Germany: Foehn Winds
France: The Mistral
Southern CA: Santa Ana Winds
Porter Ranch Fire, Oct. 14 2008, NASA image, Public Domain, http://www.nasa.gov/mission_pages/fires/main/
usa/califires_20081014.html
4
UCSD GOES-10/NASA, Public Domain, http://meteora.ucsd.edu/cap/images/junegloom_16jun2004.gif
Currents
Questions?
The Gulf Stream, Winslow Homer (1899), Metropolitan Museum of Art (NY). Public Domain,
https://commons.wikimedia.org/wiki/File:Winslow_Homer_004.jpg
Currents in the Ocean
What is a current?
Ocean currents transport water
A current is a flow of material
Wind is a current of air
MASS IS TRANSPORTED
Map by Ben Franklin, 1787
Currents in the Ocean
•  Two Types: Surface and Deep
•  Driving Forces
–  Surface Currents: Wind-driven
–  Deep Currents: Density-driven
American Meteorological Society,
http://oceanmotion.org/images/
ocean-verticalstructure_clip_image002.jpg
Ben Franklin, 1769, Map of the Gulf Stream, Public domain.
Surface Currents
Caused by: Wind Stress
Coriolis Effects
Pressure Gradients
Friction
Wind-Driven Currents
•  Wind accelerates ocean currents
–  Frictional Drag
Atmosphere
Wind
Wind
Drag
Current
Ocean
Gene Paull, UT Brownsville, Public Domain(?),
http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
Current
Map View
SIDEVIEW
TOPVIEW
Figures, UCLA
5
North Atlantic Surface Currents
Pressure-Driven Currents
•  Wind drives ocean currents
•  Currents run into continents and can’t continue
–  UNLIKE ATMOSPHERIC FLOWS
•  Water piles up ---Pressure Gradients form
60ºN
ste
We
L
Atmosphere
Wind
Drag
Wind
H
H
rlie
s
e
rli
te
Simple picture –
winds push surface
currents, water piles
up where wind blows
onto coastlines (e.g.,
Atlantic coast of S.
America).
s
es
W
30ºN
e
Trad
s
d
Tra
es
BUT: Coriolis acts on
currents!
Equator
Current
Current
Background image: U.S. Government,
extracted from PDF version of the Vol 26-4
2004 DISAM Journal (direct PDF URL [1]),
Public Domain, http://commons.wikimedia.org/
wiki/File:Globe_Atlantic.svg
L
TOPVIEW
Ocean
SIDEVIEW
Figures, UCLA
Ekman Spiral
Coriolis & currents
V. Walfrid Ekman (Sweden)
•  Currents are affected by Earth’s ROTATION!
–  This is called the “Ekman” response
•  Surface deflection 45o right of
wind (in N. Hemisphere)
•  Deflected further right with depth
•  Net (i.e., average) effect of
Ekman spiral:
Atmosphere
Transport 90º to the right of the
wind direction in the northern
hemisphere
Wind
Drag
Wind
Left of wind in the southern hemisphere
Ocean
Currents
Currents
SIDEVIEW
TOPVIEW
Figures, UCLA
Winds
Drag from the wind on surface water
~60ºN
WES
IES
TERL
WES
Horse Latitudes ~ 30o N
TRAD
E WI
NOAA image, Public Domain,
http://www.windows.ucar.edu/tour/link=/earth/Water/
ekman.html&edu=elem
TER
LIES
Horse Latitudes ~ 30o N
NDS
TRA
INDS
DE W
Equator
Figures, UCLA
Figures, UCLA
6
Wind-dragged & Basin-Edge Currents
L
Final result: a loop of current, a Gyre
H
WES
TER
LIES
Gene Paull, UT
Brownsville,
Public
Domain(?),
http://
upload.wikimedi
a.org/wikipedia/
commons/0/06/
Corrientesoceanicas.gif
Horse Latitudes ~ 30o N
TRA
N. Atlantic
Gyre
INDS
DE W
H
L
Figures, UCLA
Coriolis “Geostrophic” Response
L
One subtropical gyre is found in each hemisphere in each ocean.
Gyres rotate clockwise in the N. Hemisphere, counterclockwise in S.
Hemisphere.
Coriolis “Geostrophic” Response
H
RL
ESTE
I ES
W
Mean 1992-2002 dynamic
ocean topography, Nikolai
Maximenko (IPRC) and
Peter Niiler (SIO), Public
Domain, http://
apdrc.soest.hawaii.edu/
projects/DOT/
1992-2002MDOT.jpeg
H
Horse Latitudes ~ 30o N
TRA
H
INDS
DE W
L
Average satellite-measured “hill” of water at western side of gyre.
Figures, UCLA
QUESTIONS?
Why isn’t the high pressure in the center of the ocean?
Major Current Systems
1. 
2. 
3. 
4. 
5. 
6. 
North Atlantic gyre
South Atlantic gyre
North Pacific gyre
South Pacific gyre
Indian Ocean gyre
Antarctic Circumpolar Current
• 
Not a gyre!
Gene Paull, UT Brownsville, Public Domain(?),
http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif
7