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					                                                                                                     Introduction to Oceanography
                                                          Chris Henze, NASA Ames,

Introduction to Oceanography                                 Public Domain, http://
                                                                                               2nd Midterm November 12 (Friday).
 Lecture 16: Currents

                                                                                                 No labs on Nov. 11 (Th.) Thurs. lab students should
                                                                                          attend another section on
                                                                                           Monday, Tuesday, or
                                                                                           If you are in a Thurs. lab
                                                                                           and can’t make any
                                                                                           MTW labs let the
                                                                                           instructor know -- we
                                                                                           may schedule a special
                                                                                           Friday session.

Wind at
plane                                                                                                             Pacific surface wind forecast,
                                                                                                                     National Weather Service
altitude                                                                                                     Environmental Modeling Center/
                                                                                                            NOAA, Presumed Public Domain,

                               But wait – why do storms                                    Atmospheric Circulation including Coriolis
                        (including hurricanes and cyclones) go

                        Northern Hemisphere: Hurricane Isabel (2003) NASA,
                        Public Domain,

                                 Southern Hemisphere: Cyclone Drena (1997)
                                 NASA, Public Domain, http://

                                Questions ?                                               Figure from NASA, Public Domain,

                                                                                                  Atmospheric Circulation including Coriolis

                                                                                          •! 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
                                                                                                –! Zonal winds within each cell band
                                                         National Weather Service
                                                         Environmental Modeling Center/
                                                                                          •! DUE TO DEFLECTIONS BY CORIOLIS!
                                                         NOAA, Presumed Public

              Atmospheric Circulation including                                                                                  Atmospheric Circulation including
                          Coriolis R!                                                                                                        Coriolis
  3 Cells per hemisphere:                                                  PO
                                                                             LA                                     •! Latitudinal
     Polar                                                                                                             winds:

            Active (updraft on hot

                                                                                                                          –! 0-30o: Trade

                                                           Y! F
            side, downdraft on cold
        Ferrel                                                                                                            –! 30-60o:
               Passive (downdraft on                                                                                         Westerlies
                hot side!)                                                                                                –! 60-90o:
        Hadley                                                                                                               Polar
               Active                                                                                                        Easterlies

                                                                         UCLA figure – background image unknown.
                                                                                                                   Pidwirny, M. (2006). "Global Scale Circulation of the Atmosphere". Fundamentals of
                                                                                                                   Physical Geography, 2nd Edition.

 Atmospheric Circulation including Coriolis                                                                                                                Questions
Cell Boundaries:
                                                    Polar Front!
      60o: Polar Front
      30o: Horse
                       Horse !
         Latitudes Latitudes!
      0 o: Doldrums


Vertical air movement
  (up at Polar Front and
  Doldrums, down at
  Horse Latitudes)

Pidwirny, M. (2006). "Global Scale Circulation of the Atmosphere". Fundamentals of
Physical Geography, 2nd Edition.                             Figure from NASA, Public Domain,

      Local Meteorology of Southern California
Marine layer against the Southern California mountains
Photo by Dr. Jonathan Alan Nourse, CalPoly Pomona,,%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

                     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                                                                              away and up by cooler
  dense rising air on land.                                                                                   denser land air.

Result – wind from sea towards land                                                                   Result – wind from land towards sea
      Jesús Gómez Fernández, Wikimedia Commons, CC A S-A 3.0,        Adapted from Jesús Gómez Fernández, Wikimedia Commons, CC A S-A 3.0,
                         File:Diagrama_de_formacion_de_la_brisa-breeze.png                                                        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
 •! Cloud layer flows onto land at night
 •! Evaporates over land by day

                                    LAND!                 OCEAN!
                                                UCLA figure                                                                 Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA

                                                                                                     Santa Ana Winds

                     Santa Ana Winds                                                               Winter: Canadian cold air
                                                                                                     pushes down into
                                                                                                     Southwestern US
 •!   Canada: Chinook                                                                                 High pressure pushes dry desert air
                                                                                                        downslope, to sea
 •!   Colorado: Downslope Winds                                                                       Compression of sinking air causes
 •!   Germany: Foehn Winds                                                                            Heating lowers humidity                                             Piotr Flatau, Wikimedia Commons, Public Domain,
                                                                                                      Wind Speeds: up to ~ 70mph !115
 •!   France: The Mistral                                                                               km/hr                                                           San Gabriel/Bernardino Mtns.
                                                                                                      Funneling effect through canyons
 •!   Southern CA: Santa Ana Winds                                                                    Feeds dangerous brush fires
                                                                                                      Weaker in summer
                                                                                                                                                            High Plateau                                       Angeles
                                                                                                                                                            Mojave Desert
                                                                                                                Adapted from N. Short Remote Sensing
                                                                                                              Tutorial/NASA, Presumed Public Domain,

                NASA image, Public Domain,!                                                                                   Santa Ana Winds
                           Santa Ana Winds
                    ~ 30 mph!

                                      k  m
                                                                                                                          Santa Ana Winds:
                                                                                                                            dry & warm,
                                                                                                                            destructive fires
                                                                                                                          Fertilize ocean?
                                                                                                                          Porter Ranch Fire, NASA image, Public Domain,

UCSD GOES-10/NASA, Public Domain,

                                                                                                                                                   Currents in the Ocean
                                                                                                                                   •! What is a current?
                                                                                                                                          –! A current is a flow of material
                                                                                                                                                       –! I.e. MASS IS TRANSPORTED
                                                                                                                                                 •! Ocean currents transport seawater
                                                                                                                                                 •! Wind is also a current


                    Currents in the Ocean                                                                                                         Surface Currents
•! Two Types: Surface and Deep                                                                                            Caused by: Wind Stress                                           Pressure Gradients
                                                                                                                                                    Coriolis Effects                       Friction
•! Driving Forces
     –! Surface Currents: Wind-driven
     –! Deep Currents: Density-driven

                                                                                      American Meteorological Society,
                                                                                   vertical-structure_clip_image002.jpg   Gene Paull, UT Brownsville, Public Domain(?),

                                                                                                                           Pressure-Driven Currents
                  Wind-Driven Currents
                                                                                                                      •! Wind drives ocean currents
                                                                                                                      •! Currents run into continents and can’t continue
      •! Wind accelerates ocean currents                                                                                  –! UNLIKE ATMOSPHERIC FLOWS
          –! Frictional Drag                                                                                          •! Water piles up ---Pressure Gradients form

 Atmosphere!                                                                                                      Atmosphere!                                                          L!
                    Wind!                                                                                                       Wind!
                        Drag!                                            Wind!                                                   Drag!
                                                                                                                                                     H!                 Wind!         H!
                 Current!                                           Current!                                                  Current!                                Current!

 Ocean!                                                                                      Map View             Ocean!                                                               L!
                                   SIDEVIEW!                                          TOPVIEW!                                           SIDEVIEW!                               TOPVIEW!

     North Atlantic Surface Currents                                                                                              Coriolis & currents
                                                                     Simple picture –
                                                                    winds push surface
                                                                   currents, water piles                            •! Currents are affected by Earth’s ROTATION!
                                 60ºN                              up where wind blows                                 –! This is called the “Ekman” response
                                         li es                     onto coastlines (e.g.,
               We                  es
                                  W                                 Atlantic coast of S.
                                 30ºN                                    America).
                   es                                                                                             Atmosphere!
              Trad                      d es
                                    Tra                            BUT: Coriolis acts on
                                                                         currents!                                               Drag!

                                                                                                                              Currents!                               Currents!
                                                                         Background image: U.S. Government,
                                                                    extracted from PDF version of the Vol 26-4
                                                                    2004 DISAM Journal (direct PDF URL [1]),
                                                                 Public Domain,                            SIDEVIEW!                               TOPVIEW!

      Ekman Spiral                                                                                                                               Winds
        V. Walfrid Ekman (Sweden)
  •! Surface deflection      right of     45o
       wind (in N. Hemisphere)
•! Deflected further right with depth                                                                                                                TERL

•! Net (i.e., average) effect of
   Ekman spiral:                                                                                                                          Horse Latitudes ~ 30o N!
Transport 90º to the right of the
  wind direction in the northern
  hemisphere                                                                                                                                           E WI
Left of wind in the southern hemisphere                                                                                                        TRAD

                      NOAA image, presumed Public Domain,

   Drag from the wind on surface water                                                      Wind-dragged & Basin-Edge Currents
                                                                                               L!                                                   H!
                                             S!                                                                                 !
                                        RLIE                                                                               LIES
                                    TE                                                                                  TER
                             WES                                                                                 WES

                           Horse Latitudes ~ 30o N!                                                           Horse Latitudes ~ 30o N!

                                            NDS!                                                                                 INDS
                                   DE W
                                        I                                                                              DE W
                            TRA                                                                                     TRA

                                                                                               H!                                                   L!

   Final result: a loop of current, a Gyre                                                  Coriolis “Geostrophic” Response
                                                                                               L!                                                   H!
                                                                                                                       RL      IES!
                                                                                                                W ESTE
                                                                      Gene Paull, UT
                                                                      Brownsville, Public
                                                                      Domain(?), http://
                                                                      oceanicas.gif                                     H!
                                                                                                              Horse Latitudes ~ 30o N!

                        N. Atlantic                                                                                           INDS
                           Gyre                                                                                       DE W

                                                                                               H!                                                   L!
      One subtropical gyre is found in each hemisphere in each ocean.
     Gyres rotate clockwise in the N. Hemisphere, counterclockwise in S.

   Coriolis “Geostrophic” Response                                                                  Ocean Basin Circulation

                                                           Mean 1992-2002 dynamic
                                                                                               •! Large, circular current pattern that circulates
                                                           ocean topography, Nikolai
                                                           Maximenko (IPRC) and Peter
                                                                                                  around the subtropical ocean basin
                                                           Niiler (SIO), Public Domain,
                                                       •! Central “hill” of water ~ 1-2 m
                                                           1992-2002MDOT.jpeg                  •! Balance between Coriolis (piling up hill) and
                                                                                                  Pressure (hill wants to flow away)
                                                                                               •! Maintained by prevailing winds

Average satellite-measured “hill” of water at western side of gyre.
Why isn’t the high pressure in the center of the ocean?