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Composition of the Atmosphere Density of Air Density

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Composition of the Atmosphere Density of Air Density Introduction to Oceanography 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 Wind about 10 days 15: 15: (liquid water residence time in ocean: 3x103 years!) – Liquid evaporates into the air, then is removed as dew, rain, Lecture Lecture or snow – Warm air holds much more Atmospheric water vapor map, Sept. 13 – Nov. 2, 2017. water vapor than cold air Data from http://www.ssec.wisc.edu/data/comp/wv/ Figure by Greg Benson, Wikimedia Commons Creative Commons A S-A 3.0, http://en.wikipedia.org/wiki/File:Dewpoint.jpg Density oF Air 3 Density & temperature oF Air • Typical air density ~ 1 mg/cm 12000 – About 1/1000th the Passenger jet 10-13km density of water 10000 • Rising air expands 2000 meters • Temperature and pressure 15ºC Everest 8848m & cools afFect the density of air 15ºC • Temperature: Hot air is less 8000 – Vapor condenses dense than cold air into clouds, precipitation • Pressure: Air expands with 6000 elevation above sea level • Sinking air is Elevation (m) Elevation Mt. Whitney 4421m compressed and 1000 meters – Air is much easier to compress 4000 than water warms 24ºC 15ºC – Clear air 2000 Empire State Bldg. 450m 0 0 40000 80000 120000 34ºC Pressure (N/m2) Figure adapted from Nat’l Weather Service/NOAA, Public Domain, 15ºC Figure by E. Schauble, http://oceanservice.noaa.gov/education/yos/r using NOAA Standard Atmosphere data. esource/JetStream/synoptic/clouds.htm (1.4% H2O) Expanding Air Cools and Condenses • Like opening a pressurized bottle of soda • Air expands and cools 2000 meters 15ºC • Water vapor condenses -- cloud Formation 15ºC MMovies by J. Aurnou, E. Schauble, UCLA 1000 meters 24ºC 15ºC mov1 34ºC Figure adapted from Nat’l Weather Service/NOAA, Public Domain, 15ºC http://oceanservice.noaa.gov/education/yos/r esource/JetStream/synoptic/clouds.htm (1.4% H2O) 1 Solar Heating oF the Earth Solar Heating oF the Earth Sunlight heats the ground • Solar energy absorbed unevenly over Earth’s surFace more intensely in the • Energy absorbed / unit surFace area varies with: tropics than near poles • file:///Users/schauble/EPSS15_Oceanography/Images_ – Angle oF the sun and_movies/Insolation2.swF Heilemann CCU/NSF Flash – ReFlectivity oF the surFace (i.e., ice v. ocean) Sunlight – Transparency oF the atmosphere (i.e., clouds) intensity (top oF atmosphere) Sunlight intensity (ground) PrZemyslaw "Blueshade" IdZkiewicZ, Figure by William M. Connolley using Creative Commons A S-A 2.0, HadCM3 data, Wikimedia Commons, Creative http://commons.wikimedia.org/wiki/Fi Commons A S-A 3.0, le:Earth-lighting-winter- http://commons.wikimedia.org/wiki/File:Insolati solstice_EN.png on.png Solar Heating & the Seasons Solar Heating & the Seasons June 20-21: N. Not to scale! March 20-21: Sun Pole tilted shines on both poles towards Sun May 9: We equally are here Sept. 22-23: Sun Dec 21-22: N. shines on both poles Pole tilted away equally from Sun Background image: Tauʻolunga, Creative Commons A S-A 2.5, http://en.wikipedia.org/wiki/File:North_season.jpg • Seasons are caused by Earth’s 23.5o tilt NASA animation by Robert Simmon, Public Domain, data ©2011 EUMETSAT • Northern summer: north hemisphere points at sun http://earthobservatory.nasa.gov/IOTD/view.php?id=52248&src=ve 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 2 Redistribution oF Solar Heat Energy 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.wikime dia.org/ wiki/File:Earth_equator _northern EQUATOR _hemisphere.png Warm, less dense air rises near the Equator POLES • Convective heat transFer moderates Earth climate • Heated air expands & rises, then cools & sinks Cold, more dense air Adapted from image at http://www.yourhome.gov.au/technical/images/62a.jpg, Public Domain? sinks near the Poles The Coriolis EfFect on Earth The Coriolis EFFect • To an Earthbound observer (i.e., us): • Northern Hemisphere: Earth’s • SurFace velocity rotation causes moving things to increases From pole to curve to their right equator • Points on the equator Moving things: Air masses, oceanic Flows, must move Faster than missiles, anything with mass points near the poles to go around once a day • Latitude velocity diFFerences lead to curving paths – Example: Merry-go round • Southern Hemisphere: Earth’s rotation causes moving things to curve to their left National Snow and Ice Data Center, free National Snow and Ice Data Center, free for educational for educational use, use, http://nsidc.org/arcticmet/factors/winds.html http://nsidc.org/arcticmet/factors/winds.ht ml But wait – why do storms Atmospheric Circulation including Coriolis (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/199 7/drena.vis.gif (now moved) Questions ? Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html 3 Atmospheric Circulation including Coriolis Actual • 3 convection cells in each hemisphere forecast of – Each cell: ~ 30o latitudinal width surFace winds • Vertical Motions – Rising Air: 0o and 60o Latitude – Sinking Air: 30o and 90o Latitude • Horizontal Motions – Zonal winds Flow nearly along latitude lines Pacific surface wind forecast-hindcast, National Weather Service – Zonal winds within each cell band Environmental Modeling Center/NOAA, Public Domain, GIF by E. Schauble • DUE TO DEFLECTIONS BY CORIOLIS! using EZGif Atmospheric Circulation including Atmospheric Circulation including Coriolis Coriolis 3 Cells per hemisphere: • Latitudinal Polar winds: Active (updraFt on hot – 0-30o: side, downdraFt on cold Trade side) Winds Ferrel o Passive (downdraFt on – 30-60 : hot side!) Westerlies Hadley – 60-90o: Active Polar Easterlies UCLA figure – background image unknown. 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 Questions Cell Boundaries: Polar Front 60o: 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 Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html 4 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 Sea Breeze Land Breeze Land cools Fastest Land warms Fastest at night. Air during the day. Air contracts and sinks expands and rises Ocean surface Ocean surface temperature changes temperature changes slowly. Air is pushed slowly. Air displaces less T away and up by cooler dense rising air on land. hi denser land air. s Result – wind From sea towards land Result – wind From land towards sea Jesús GómeZ FernándeZ, Wikimedia Commons, Creative Commons A S-A 3.0, 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 http://commons.wikimedia.org/wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.png Marine Layer UCLA 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 OCEAN UCLA figure Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA 5.
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