Introduction to Oceanography Chris Henze, NASA Ames,...
Transcript of Introduction to Oceanography Chris Henze, NASA Ames,...
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Lect
ure
10: W
ind
Introduction to Oceanography Chris Henze, NASA Ames, Public Domain, http://people.nas.nasa.gov/
~chenze/fvGCM/frances_02.mpg
Winds at ~jet plane
altitude
Introduction to Oceanography
Pacific surface wind forecast-hindcast, National
Weather Service Environmental Modeling
Center/NOAA, Public Domain, GIF by E. Schauble
using EZGif
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pH Scale • pH scale = Logarithmic scale
• Neutral (pure) water:
– 1/(5.5x108) water molecules is disassociated – there are about 55 moles of water per liter Concentration of H+= 55/(5.5x108) = 10–7 moles/liter
– Neutral water pH = 7 • lower pH = acid, higher pH = base
€
pH = − log10(H +)
pH Scale
Stephen Lower, Wikimedia Commons,
CC A S-A 3.0, http://en.wikipedia.org/wiki/
File:PH_scale.png
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The Carbonate Buffer System • Seawater pH = ~8.0 (slightly basic) • Maintained by carbonate buffer system:
• Increase CO2 in water, acidity increases What happens to pH?
• Add acid and CO2 is produced
€
CO2 + H2O ⇔ H2CO3 ⇔ H+ + HCO3− ⇔ 2H+ + CO3
2–
Carbonic Acid Bicarbonateion
Carbonateion
The CO2 system and carbonate
• Deep waters form at the poles: High CO2 and therefore acidic
• Acidity interacts to dissolve calcium carbonate (CaCO3) deposits on the deep sea floor – Acidity and temperature control carbonate
compensation depth (CCD)
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Questions
Image from UNESCO, Presumed Public Domain, http://ioc3.unesco.org/oanet/FAQacidity.html
Wind
• Lecture 8: Atmospheric Circulation
Wind sea, N. Pacific, Winter 1989, M/V NOBLE STAR/NOAA, Public Domain, http://commons.wikimedia.org/ wiki/File:Wea00816.jpg
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Atmosphere-Ocean Coupling
• Why study atmospheric circulation? – Atmosphere & ocean processes are
intertwined – Atmosphere-ocean interaction moderates
surface temperatures, weather & climate • Weather: local atmospheric conditions • Climate: regional long-term weather
– Atmosphere drives most ocean surface waves and currents (our next topic)
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: 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 pressure affect the density of air
• Temperature: Hot air is less dense 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
Ele
vatio
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
15ºC 15ºC
24ºC 15ºC
34ºC 15ºC
(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
15ºC 15ºC
24ºC 15ºC
34ºC 15ºC
(1.4% H2O)
Questi
ons
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
23.5º
Solar Heating of the Earth Sunlight 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 Seasons Not to scale!
Oct. 26: 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
equally Background 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 EUMETSAT http://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
EQU
ATOR
POLE
S
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.or
g/ wiki/File:Earth_equator
_northern _hemisphere.png
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Questions
Not quite right!
ACTUAL Atmospheric Circulation
Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html
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Lab Coriolis Movies
• Movies made by Rob Hyde, UCLA
Lab Coriolis Movies
Stat
iona
ry O
bser
ver
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Lab Coriolis Movies C
CW
Rot
atio
n, 2
5 rp
m
Lab Coriolis Movies
CW
Rot
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n, 4
1 rp
m
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Coriolis Effect Movies
Movie: University of Illinois (not sure if that’s the original source) http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/crls.rxml
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
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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
• Strength of Deflection varies with latitude: – Maximum at the poles – Zero(!) at equator
– Faster a planet rotates, the stronger the Coriolis effects
– The larger the planet, the stronger the Coriolis effects
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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)
Ferrel Passive (downdraft on
hot side!) Hadley
Active H
AD
LEY
POLAR
FERREL
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 Coriolis Cell 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 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
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