Introduction to Oceanography Lecture 15: Wind 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 1
Typical air density ~ 1 mg/cm 3 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 Density of Air Elevation (m) 12000 10000 8000 6000 4000 Mt. Whitney 4421m Passenger jet 10-13km Everest 8848m 2000 Empire State Bldg. 450m 0 0 40000 80000 120000 Pressure (N/m 2 ) Figure by E. Schauble, using NOAA Standard Atmosphere data. Density & temperature of Air Rising air expands & cools Vapor condenses into clouds, precipitation Sinking air is compressed and warms Clear air 2000 meters 1000 meters 24ºC Figure adapted from Nat l Weather Service/NOAA, Public Domain, http://oceanservice.noaa.gov/education/yos/r esource/jetstream/synoptic/clouds.htm 34ºC (1.4% H 2 O) 2
Expanding Air Cools and Condenses Like opening a pressurized bottle of soda Air expands and cools Water vapor condenses -- cloud formation MMovies by J. Aurnou, E. Schauble, UCLA mov1 2000 meters 1000 meters 24ºC Figure adapted from Nat l Weather Service/NOAA, Public Domain, http://oceanservice.noaa.gov/education/yos/r esource/jetstream/synoptic/clouds.htm 34ºC (1.4% H 2 O) 3
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/fi le:earth-lighting-wintersolstice_en.png 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:insolati on.png 4
June 20-21: N. Pole tilted towards Sun Solar Heating & the Seasons Not to scale! May 9: We are here March 20-21: Sun shines on both poles equally 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 23.5 o tilt Northern summer: north hemisphere points at sun 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 5
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 6
Redistribution of Solar Heat Energy POLES EQUATOR Convective heat transfer moderates Earth climate Heated air expands & rises, then cools & sinks 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.wikime dia.org/ wiki/file:earth_equator _northern _hemisphere.png Warm, less dense air rises near the Equator Cold, more dense air sinks near the Poles 7
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 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 The Coriolis Effect 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.ht ml 8
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/199 7/drena.vis.gif (now moved) Questions? Atmospheric Circulation including Coriolis Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html 9
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: ~ 30 o latitudinal width Vertical Motions Rising Air: 0 o and 60 o Latitude Sinking Air: 30 o and 90 o Latitude Horizontal Motions Zonal winds flow nearly along latitude lines Zonal winds within each cell band DUE TO DEFLECTIONS BY CORIOLIS! 10
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 UCLA figure background image unknown. Atmospheric Circulation including Coriolis Latitudinal winds: 0-30 o : Trade Winds 30-60 o : Westerlies 60-90 o : Polar Easterlies Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic, http://en.wikipedia.org/wiki/file:atmosphcirc2.png 11
Atmospheric Circulation including Coriolis Cell Boundaries: 60 o : Polar Front 30 o : Horse Latitudes Horse Latitudes Doldrums 0 o : Doldrums Vertical air movement (up at Polar Front and Doldrums, down at 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 12
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 13
Sea Breeze Land warms fastest during the day. Air expands and rises Ocean surface temperature changes slowly. Air displaces less dense rising air on land. This image cannot currentl y be display 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. 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 14
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 UCLA Marine Layer Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA 15