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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

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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,

http://oceanservice.noaa.gov/education/yos/resource/JetStream/synoptic/clouds.htm

2000 meters

1000 meters

15ºC15ºC

24ºC15ºC

34ºC15ºC

(1.4% H2O)

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Expanding Air Cools and Condenses

mov1

• Like opening a pressurized bottle of soda• Air expands and cools• Water vapor condenses -- cloud formation

MMovies by J. Aurnou, E. Schauble, UCLA

2000 meters

1000 meters

15ºC15ºC

24ºC15ºC

34ºC15ºC

(1.4% H2O)

Figure adapted from Nat’l Weather Service/NOAA, Public Domain,

http://oceanservice.noaa.gov/education/yos/resource/JetStream/synoptic/clouds.htm

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Solar Heating of the Earth• Solar energy absorbed unevenly over Earth’s surface• Energy absorbed / unit surface area varies with:

– Angle of the sun– Reflectivity of the surface (i.e., ice v. ocean)– Transparency of the atmosphere (i.e., clouds)

Przemyslaw "Blueshade" Idzkiewicz,Creative Commons A S-A 2.0,

http://commons.wikimedia.org/wiki/File:Earth-lighting-winter-

solstice_EN.png

Solar Heating of the EarthSunlight heats the ground

more intensely in the tropics than near poles

• file:///Users/schauble/EPSS15_Oceanography/Images_and_movies/Insolation2.swf Heilemann CCU/NSF

Flash

Sunlight intensity (top of atmosphere)

Sunlight intensity (ground)

Figure by William M. Connolley using HadCM3 data, Wikimedia Commons, Creative Commons A S-A 3.0,http://commons.wikimedia.org/wiki/File:Insolation.png

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• Seasons are caused by Earth’s 23.5o tilt• Northern summer: north hemisphere points at sun

Solar Heating & the SeasonsNot to scale!

May 9: We are here

Dec 21-22: N. Pole tilted away

from Sun

June 20-21: N. Pole tilted

towards Sun

March 20-21: Sun shines on both poles

equally

Sept. 22-23: Sun shines on both poles

equallyBackground image: Tauʻolunga, Creative Commons A S-A 2.5, http://en.wikipedia.org/wiki/File:North_season.jpg

Solar Heating & the Seasons

NASA animation by Robert Simmon, Public Domain, data ©2011 EUMETSAThttp://earthobservatory.nasa.gov/IOTD/view.php?id=52248&src=ve

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Redistribution of Solar Heat Energy

• 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

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Questions ?

Southern Hemisphere: Cyclone Drena (1997) NASA, Public Domain, http://www.ngdc.noaa.gov/dmsp/hurricanes/1997/drena.vis.gif (now moved)

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

Mediterranean Climate• LA: Subtropical latitude, abutting ocean• Subsiding flow: sinking air

– Clear most of the year• Effects of coast:

– Higher humidity--- thermal buffer• Winter Storms

– 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

away and up by cooler denser land air.

Result – wind from land towards sea

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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

LAND OCEANUCLA figure

UCLA Marine Layer

Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA