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large scale (Subject) / Part 2 (Lesson)

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• ocean currents Surface current > 10% of ocean - wind driven - above pycnocline Depp current >90% - density driven - below pycnocline
• Trade winds Westerlies trade winds between 0°-30° blow currents to the west westerlies between 30°-60° blow surface currents to the east
• molecular viscosity eddy viscosoty a) laminar flow: momentum transfer between molecules of different layers b) turbulences in currents so not individual molecules moved but parcels of molecules > lead to higher friction
• Gyres respond to main ind belts main gyres (5) North and south pacific north and south atlantic indian
• wind stress in general its a friction force (horizontal force)/per unit of area > influenced by: prevailing atmospheric conditions, wind speed, roughness of the sea surface >wind stress causes transfer of momentum: a) surface waves, drift currents (3%of wind speed)
• eddy viscosity coefficient have in vertical direction (Az)  and in horizontal (AH) horizontal value is much higher because ocean is very stable in the vertical and a lot more mixing occurs in the horizontal
• Ekamn theory Force equilibrium When wind starts to move it induces movement in the surface.  Due to coriolis force current deflects to the right  the current velocity is constant when coriolis force, wind induced force and friction force between the parcels are in equilibrium  -> 45° deflection of surface current to the right from wind direction
• ekman theory - wind induced circulation - Conditions developing a model ocean > no horizontal eddy coeffizient and vertical is constant >barotropic conditions (no differences in density horizontal) > no horizontal pressure gradient > no slope in surface > layers are influenced by coriolis force >no advection terms - linear model
• ekman velocity currents velocitiy only induced by wind - seperate from geostrophic current - fv = f(vekman + vgeo)
• ekman velocity calculation and at equator velocity decades exponentially with depth _spiral when z= DE (depth of ekman layer) the current moves oppisitional to wind  at equator f=0 so not solvable > no ekman spiral at equator
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• ekman depth here the current is directly opposed to wind and its velocity is 1/23 of the surface thus neglible the depth depends on the eddy viscosity coefficient and the latitude the direction of the stream in a layer is reflected to the right and the layer below again to the right and the layer below again to the right
• mean ekman transport 90° to the right from the wind  = net movement  and water from bottom rises up in a spiral
• bottom friction and geostrophic velocity the bottom friction reduces the geostrophic currents velocity thus coriolis forces alo decreases and the current deflects back to the left. balanced again when deflected 45°
• ekman pumping wind moves cyclonic (anticlockwise) the ekman transport is nach außen > divergence and water needs to be replaced by bottom water = upwelling > Ekamn suction wind moves anticyclonic - ekman transport nach innen > convergence > downwelling > ekman pumping induces a slope in the surface thus a geostrophic flow
• geostrophic current in the gyre anticyclonic = convergence : right: geostrophic current goes out and on the left side goes in opposite for cyclonic
• western intensification center of gre is moved to the west due to wearth rotation  >intensification in the western currents
• equatorial upwelling mathematically ekman transport not working at equator, however, it can be observed: trade winds lead to divergence thus upwelling. geostrophic current moves same direction bc of deflection change due to southern and nothern hemisphere - both go into the board
• main upwelling region a)canary current b)peru current c) benguela current d)california current
• wind stress curl positive: offshore stronger wind thus ekamn transport also stronger which leads to divergence and thus more upwellling negative: offshore wind is less thus ekmann transport is less which leads to convergence - downwelling
• summary convergence divergence anitcyclonic = clockwise = negativ = convergence cyclonic = anticlockwise = positivw = divergence
• relaitve vorticity = der vertikale teil aus dem kreuzprodukt des gradienten und der geschwindikeit  = vorticity ist perpendicular zur horizontal geschwindigkeit
• skalarprodukt von gradient und vektor = divergence = wenn negativ dann convergence
• 3 types of vorticity • Absolute vorticity ( ~ωa) = vorticity as viewed in an inertial reference frame.• Relative vorticity (~ζ) = vorticity as viewed in the rotating reference frame of theEarth.• Planetary vorticity ( ~ωp) = vorticity associated with the rotation of the Earth. ~ωa = ~ζ + ~ωp  where ~ωa = ∇ × ~vI ,~ζ = ∇ × ~vR and ~ωp = 2Ω.
• f-plane beta-plane f-plane = f is constant β-plane - f changes with latitude - vorticity changes with latitude
• continuity equation in fluid dynamics describes that in any steady state process, the rate at which mass leaves the system is equal to the rate at which mass enters a system
• potential vorticity (rel. vorticity + f)/D  > conservation of potential vorticity as it is constant  thus when D decreases, rel. vorticity decreases and anticyclonic vortex  when D is increasing rel, vorticity needs to increse (+) thus cyclonic  f is seen constant unless its a flow over a long distance. then rel. vort. is constant and f changes
• conservation of potential vorticity when die layer (D) kleiner wird dann muss rel. vorticity auch kleiner werden (-) = anticyclonic vortex when D increases rel. vorticity has to increase (+) = cyclonic movement
• langmuir circulation transient wind induced horizontal tubes below surface. >cells formed when small surface waves are damped one cell moves clockwise and the adjecent tubes moves counterclockwise resulting in a up and downwelling effect.  happens within minutes (ekman within hours) and mostly move along wind direction > convergence forms streaks on the surface  (downwelling speed around 1/3 of the wind) >wave anergy is transfered to trubulent energy and mixed layer deepens

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