Questions? Santa Ana Winds. Santa Ana Winds. Santa Ana Winds. Introduction to Oceanography. Midterm 2: Nov. 20 (Monday) Lecture 17, Current.

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1 Introduction to Oceanography ecture 17, Midterm 2: Nov. 20 (Monday) Review Session & Video Screenings TBA NOAA Ocean-Atmosphere Sea Surface Temperature Model, Public Domain, Breaking wave and sea foam, Vero Beach, F, Robert awton, Creative Commons A S-A 2.5, Santa Ana s Winter: Canadian cold air pushes down into Southwestern US igh pressure pushes dry desert air downslope, to sea Compression of sinking air causes heating eating lowers humidity 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, c.jpg Piotr Flatau, Wikimedia Commons, Public Domain, igh Plateau Mojave Desert San Gabriel/Bernardino Mtns. os Angeles NASA image, Public Domain, Santa Ana s ~ 30 mph Santa Ana s UCSD GOES-10/NASA, Public Domain, Santa Ana s: dry & warm, Encourage destructive fires Fertilize ocean? Porter Ranch Fire, Oct , NASA image, Public Domain, Questions? 1

2 s s in the Ocean What is a current? A current is a flow of material MASS IS TRANSPORTED Ocean currents transport water is a current of air Map by Ben Franklin, 1787 Portrait of Ben Franklin, 1785, by Duplessis The Gulf Stream, Winslow omer (1899), Metropolitan Museum of Art (NY). Public Domain, Ben Franklin, 1769, Map of the Gulf Stream, Public domain. s in the Ocean Two Types: Surface and Deep Driving Forces Surface s: -driven Deep s: Density-driven Surface s Caused by: Stress Pressure Gradients Coriolis Effects Friction American Meteorological Society, ean-verticalstructure_clip_image002.jpg -Driven s accelerates ocean currents Frictional Drag Pressure-Driven s drives ocean currents s run into continents and can t continue UNIKE ATMOSPERIC FOWS Water piles up ---Pressure Gradients form Atmosphere Atmosphere Drag Drag Ocean SIDEVIEW Map View TOPVIEW Ocean SIDEVIEW TOPVIEW 2

3 North Atlantic Surface s 60ºN 30ºN Equator Simple picture winds push surface currents, water piles up where wind blows onto coastlines (e.g., Atlantic coast of S. America). BUT: Coriolis acts on currents! Coriolis & currents s are affected by Earth s ROTATION! This is called the Ekman response Atmosphere Drag Background image: U.S. Government, extracted from PDF version of the Vol DISAM Journal (direct PDF UR [1]), Public Domain, Atlantic.svg Ocean s SIDEVIEW s TOPVIEW Ekman Spiral V. Walfrid Ekman (Sweden) Surface deflection 45 o right of wind (in N. emisphere) Deflected further right with depth Net (i.e., average) effect of Ekman spiral: Transport 90º to the right of the wind direction in the northern hemisphere eft of wind in the southern hemisphere s ~60ºN orse atitudes ~ 30 o N NOAA image, Public Domain, ml&edu=elem Equator Drag from the wind on surface water -dragged & Basin-Edge s orse atitudes ~ 30 o N orse atitudes ~ 30 o N 3

4 Final result: a loop of current, a Gyre Coriolis Geostrophic Response N. Atlantic Gyre Gene Paull, UT Brownsville, Public Domain(?), media.org/wikipe dia/commons/0/0 6/Corrientesoceanicas.gif orse atitudes ~ 30 o N One subtropical gyre is found in each hemisphere in each ocean. Gyres rotate clockwise in the N. emisphere, counterclockwise in S. emisphere. Coriolis Geostrophic Response QUESTIONS? Mean dynamic ocean topography, Nikolai Maximenko (IPRC) and Peter Niiler (SIO), Public Domain, du/projects/dot/ mdot.jpeg Average satellite-measured hill of water at western side of gyre. Why isn t the high pressure in the center of the ocean? Major Systems Major Systems 1. North Atlantic gyre 2. South Atlantic gyre 3. North Pacific gyre 4. South Pacific gyre 5. Indian Ocean gyre 6. Antarctic Circumpolar Not a gyre! S. Pacific N. Atlantic S. Atlantic Indian N. Pacific 4

5 s on each edge of a Gyre have names. Transverse Transverse s Driven primarily by Stress Antarctic Circumpolar is the largest of these Transverse Cropped from Antarctic Circumpolar Not a gyre! Southern Westerlies drive largest volume current on Earth 100 x 10 6 m 3 /s on average. 600 times the flow of the Amazon! Equatorial s Found on either side of the equator Flow to the west WY? Constant strong westerly winds No continents to disrupt flow in southern ocean ome of the most violent seas on Earth Storm waves, Southern Ocean, R. Easther, Australian Antarctic Division, Western Boundary s North Atlantic Gyre Boundary s Gulf Stream Cold, cold Northern Canada Temperate Northern Europe British National Centre for Ocean Forecasting, Public Domain(?), a/cssgif/mapwithrectangle.g if Red -- Warm surface waterblue -- Cold surface water Sea Surface eight (cm) Distance (km) 5

6 Coriolis Geostrophic Response Centers of gyre hills : Sargasso Sea, W. Pacific, Madagascar, etc. Animation from the Naval Research aboratory, Public Domain, flow rate in the Gulf Stream, in units of 10 6 m 3 /sec (roughly: millions of tons/sec) 10 6 m 3 /sec = 60 Mississippi Rivers! Image from Sverdrup, Johnson, and Fleming, Sverdrup.U., Johnson M.W., Fleming R.. The Oceans.. their physics, chemistry, and general biology (1942), Gulf Stream time-lapse Surface Temp. Western Boundary s Fastest, deepest gyre currents Equatorial currents are deflected to high latitudes by continents Transport warm water to high latitudes Gulf Stream (N. Atlantic); Kuroshio (N. Pacific); Brazil (S. Atlantic); Agulhas (Indian); East Australian (S. Pacific) Gulf Stream is king of them all! 2 m/s 200 km/day 55x10 6 m 3 /sec = 55 Sverdrups transported > 3000 Mississippi Rivers! U. Miami /CIMAS, Public Domain. Eastern Boundary s Shallow, broad, slow currents Return flow to low latitudes Transport cold water to the equator Roughly 1/10 the speed of WBCs Canary (N. Atlantic); California (N. Pacific); Benguela (S. Atlantic); West Australian (Indian); Peru (S. Pacific) Boundary s Width (km) Depth (km) Flow Rate (km/day) Western Boundary Eastern Boundary < 100 km 1-2 km ~ 100 km/day > 1000 km < 0.5 km ~ 10 km/day 6