Introduction to Oceanography Lecture 16: Wind 2 Wind speed and direction about 1.5 km above sea level By Trent Schindler (NASA) using satellite data. Public Domain https://svs.gsfc.nasa.gov/4571 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 1
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 2
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 3
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! 4
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 5
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 6
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 7
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. 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 8
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 9
Santa Ana Winds Canada: Chinook Colorado: Downslope Winds Germany: Foehn Winds France: The Mistral Southern CA: Santa Ana Winds Santa Ana Winds Winter: Canadian cold air pushes down into Southwestern US High pressure pushes dry desert air downslope, to sea Compression of sinking air causes heating Heating lowers humidity Wind Speeds: up to ~ 70mph 115 km/hr Funneling effect through canyons Feeds dangerous brush fires Weaker in summer Adapted from N. Short Remote Sensing Tutorial/NASA, Public Domain, http://rst.gsfc.nasa.gov/sect14/katabati c.jpg Piotr Flatau, Wikimedia Commons, Public Domain, http://en.wikipedia.org/wiki/file:santa_ana_wind1.jpg High Plateau Mojave Desert San Gabriel/Bernardino Mtns. Los Angeles 10
NASA image, Public Domain, http://photojournal.jpl.nasa.gov/catalog/pia03892 Santa Ana Winds ~ 30 mph Santa Ana Winds Santa Ana Winds: dry & warm, Encourage destructive fires Fertilize ocean? Porter Ranch Fire, Oct. 14 2008, NASA image, Public Domain, http://www.nasa.gov/mission_pages/fires/main/usa/califires_20081014.html 11
Santa Ana Winds Canada: Chinook Colorado: Downslope Winds Germany: Foehn Winds France: The Mistral Southern CA: Santa Ana Winds UCSD GOES-10/NASA, Public Domain, http://meteora.ucsd.edu/cap/images/junegloom_16jun2004.gif Questions? 12
Currents The Gulf Stream, Winslow Homer (1899), Metropolitan Museum of Art (NY). Public Domain, https://commons.wikimedia.org/wiki/file:winslow_homer_004.jpg Currents in the Ocean What is a current? A current is a flow of material MASS IS TRANSPORTED Ocean currents transport water Wind is a current of air Map by Ben Franklin, 1787 Portrait of Ben Franklin, 1785, by Duplessis Ben Franklin, 1769, Map of the Gulf Stream, Public domain. 13
Currents in the Ocean Two Types: Surface and Deep Driving Forces Surface Currents: Wind-driven Deep Currents: Density-driven American Meteorological Society, http://oceanmotion.org/images/oc ean-verticalstructure_clip_image002.jpg Surface Currents Caused by: Wind Stress Coriolis Effects Pressure Gradients Friction Gene Paull, UT Brownsville, Public Domain(?), http://upload.wikimedia.org/wikipedia/commons/0/06/corrientes-oceanicas.gif 14
Wind-Driven Currents Wind accelerates ocean currents Frictional Drag Atmosphere Wind Ocean Drag Current SIDEVIEW Wind Current Map View TOPVIEW Figures, UCLA Pressure-Driven Currents Wind drives ocean currents Currents run into continents and can t continue UNLIKE ATMOSPHERIC FLOWS Water piles up ---Pressure Gradients form Atmosphere Wind L Drag H Wind H Ocean Current SIDEVIEW Current L TOPVIEW Figures, UCLA 15