1 Lecture 15: Wind Introduction to Oceanography Atmospheric water vapor map, Sept. 13 – Nov. 2, 2017. Data from http://www.ssec.wisc.edu/data/comp/wv/ Composition of the Atmosphere • Dry Air: 78% Nitrogen, 21% Oxygen • BUT it is never completely dry – Typically contains about 1% water vapor Chemical residence time of water vapor in the air is about 10 days (liquid water residence time in ocean: 3x10 3 years!) – Liquid evaporates into the air, then is removed as dew, rain, or snow – Warm air holds much more water vapor than cold air Figure by Greg Benson, Wikimedia Commons Creative Commons A S-A 3.0, http://en.wikipedia.org/wiki/File:Dewpoint.jpg
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Composition of the Atmosphere - UCLAschauble/EPSS15_Oceanography/... · 6 Redistribution of Solar Heat Energy • Equator absorbs more heat from the sun than it radiates away (net
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1
Lect
ure
15: W
ind
Introduction to Oceanography
Atmospheric water vapor map, Sept. 13 – Nov. 2, 2017.Data from http://www.ssec.wisc.edu/data/comp/wv/
Composition of the Atmosphere• Dry Air: 78% Nitrogen, 21% Oxygen• BUT it is never completely dry
– Typically contains about 1% water vaporChemical residence time of water vapor in the air is
about 10 days(liquid water residence time in
ocean: 3x103 years!)– Liquid evaporates into the air,
then is removed as dew, rain, or snow
– Warm air holds much more water vapor than cold air
Figure by Greg Benson, Wikimedia Commons Creative Commons A S-A 3.0,
http://en.wikipedia.org/wiki/File:Dewpoint.jpg
2
Density of Air• Typical air density ~ 1 mg/cm3
– About 1/1000th the density of water
• Temperature and pressureaffect the density of air
• Temperature: Hot air is lessdense than cold air
• Pressure: Air expands with elevation above sea level– Air is much easier to compress
than water
Figure by E. Schauble, using NOAA Standard Atmosphere data.
0
2000
4000
6000
8000
10000
12000
0 40000 80000 120000
Elev
atio
n (m
)
Pressure (N/m2)
Everest 8848m
Passenger jet 10-13km
Mt. Whitney 4421m
Empire State Bldg. 450m
Density & temperature of Air
• Rising air expands & cools– Vapor condenses
into clouds, precipitation
• Sinking air is compressed and warms– Clear air
Figure adapted from Nat’l Weather Service/NOAA, Public Domain,
• Equator absorbs more heat from the sun than it radiates away (net > 0).• Polar regions radiate much more heat than they absorb from the sun(!)• E.g., Equator isn’t that Hot; Poles aren’t that Cold• Evidence that the atmosphere (~2/3) & oceans (~1/3) redistribute heat• Result: convective heat transfer moderates climate
CERES/NASA animation, Public Domain, http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=CERES_NETFLUX_M
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Redistribution of Solar Heat Energy
• Convective heat transfer moderates Earth climate• Heated air expands & rises, then cools & sinks
EQUATO
R
POLES
Adapted from image at http://www.yourhome.gov.au/technical/images/62a.jpg, Public Domain?
Atmospheric Circulation Without Rotation
Warm, less dense air rises
near the Equator
Cold, more dense air sinks near the Poles
Cold, more dense air sinks near the Poles
Background image from Smári P.
McCarthy, Creative Commons A S-A 3.0,
http://commons.wikimedia.org/
wiki/File:Earth_equator_northern
_hemisphere.png
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The Coriolis Effect on Earth
National Snow and Ice Data Center, free for educational use, http://nsidc.org/arcticmet/factors/winds.html
• 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
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
Northern Hemisphere: Hurricane Isabel (2003) NASA, Public Domain, http://visibleearth.nasa.gov/view_rec.php?id=5862
But wait – why do storms(including hurricanes and cyclones) go
backwards?
Atmospheric Circulation including Coriolis
Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html
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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
Atmospheric Circulation including Coriolis
• 3 convection cells in each hemisphere– Each cell: ~ 30o latitudinal width
• Vertical Motions– Rising Air: 0o and 60o Latitude– Sinking Air: 30o and 90o Latitude
• Horizontal Motions– Zonal winds flow nearly along latitude lines– Zonal winds within each cell band
• DUE TO DEFLECTIONS BY CORIOLIS!
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Atmospheric Circulation including Coriolis
3 Cells per hemisphere:Polar
Active (updraft on hot side, downdraft on cold side)
FerrelPassive (downdraft on
hot side!)
HadleyActive
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
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Atmospheric Circulation including CoriolisCell Boundaries:
60o: Polar Front
30o: Horse Latitudes
0o: Doldrums
Vertical air movement(up at Polar Front and Doldrums, down at Horse Latitudes)
Doldrums
Horse Latitudes
Polar Front
Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic, http://en.wikipedia.org/wiki/File:AtmosphCirc2.png
Questions
Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html
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Local Meteorology of Southern CaliforniaMarine layer against the Southern California mountainsPhoto by Dr. Jonathan Alan Nourse, CalPoly Pomona, http://geology.csupomona.edu/janourse/Storms,%20Floods,%20Landslides.htm
– Pole-equator temp difference larger in winter– Speeds up jet stream, big storms get pushed our
way
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Sea Breeze
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 warms fastest during the day. Air expands and rises
Ocean surface temperature changes
slowly. Air displaces less dense rising air on land.
Result – wind from sea towards land
This image cannot currently be display
Land Breeze
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 cools fastest at night. Air
contracts and sinks
Ocean surface temperature changes slowly. Air is pushed