Midterm ReviewSea Water PropertiesSlide 3Density (the key property)Mixing & TurbulenceBuoyancyConvection & the Conveyor BeltThe AtmosphereSlide 9Ekman TransportSlide 11Slide 12Inertia CurrentsHorizontal Pressure GradientsDynamic HeightBarotropic ConditionsBaroclinic vs. BarotropicDivergence and ConvergenceThe Gulf StreamVorticityWestern IntensificationSlide 22Coastal UpwellingGeog 163 – Ocean CirculationMidterm ReviewGeography 163 Spring 2010 Midterm Study GuideThe following is a list of some concepts we have covered so far this quarter. Keep in mind that this list is not everything we’ve covered and some may or may not be on the midterm exam. If you’ve been doing the assigned readings, have attended lecture, and have put effort into doingthe homework you should do well. I suggest going over your notes and the lecture notes posted online.http://www.icess.ucsb.edu/~davey/Geog163/The Midterm is Tuesday 05/11/2010BRING A CALCULATOR!!!Sea Water PropertiesPure water (96.5%);Dissolved salts, gases, organic substances, and particles (3.5% );Physical properties are mainly determined by pure water.Hydrogen Bonding:•Ice crystals are less dense than liquid water;•Maximum density is water at 4°C.As lakes cool they reach temperature of maximum density (4°C) & overturn;Later ice forms at the surface, sheltering the interior from winter conditions;This allows fish over winter under the ice.Fundamental seawater properties:•Salinity, temperature & pressure.Density is the important variable.Sea Water PropertiesSalinity :•[mass “salts”]/[mass seawater]•The “salts” (Cl-, SO4-2, Na+, K+, etc.) are in approximate constant proportion•Law of salinity (residence time is huge)•Measure one ion [Cl-] - estimate salinity•Units are “practical salinity units” (psu)Temperature:•Generally decreases with depth in the ocean•Except where ice is formed, temperature changes primarily regulate density•Rule of thumb:  = +1 kg m-3 for T = -5 CPressure:•weight of sea water lying above a depth (hydrostatic)•Pressure varies from 0 to >5000 db•p = 0 is atmospheric pressure•Note: 1 db pressure ~ 1 m depthFeatures:•Mixed layer•Thermocline•HaloclineDensity (the key property)Changes in vertical - inhibit mixingChanges in horizontal - drive currentsControled by:•temperature•salinity (dissolved salt content)•pressure (related to depth)in situ density (S,T,p)Sigma-t (S,T,0) – 1000Sigma- (S,q,0) – 1000Rules of thumb   = +1 kg m-3  T = -5C, S = 1 psu or p = 100 dbMixing & TurbulenceMixing leads to a homogenization of water mass propertiesMixing occurs on all scales in ocean•molecular scales (10’s of mm)•basin scales (1000’s of km)Turbulence interactions cascade energy from big to small scales 10 cm eddies•Small-scale turbulence•Shear-driven200 km eddies•Mesoscale•GeostrophicBuoyancyDense water sinks - light water floatsDensity profile will increase with depthUpward force due to ’s in  is called the buoyancy forceBuoyancy restricts vertical mixing of water massesBuoyancy is important to vertical mixing:•Asymmetric mixing in ocean interior•ConvectionWaters of same  mix easily, waters of different don’t (oil & vinegar)Potential energy differences must be overcome by mechanical energy inputsMixing along isopycnal surfaces will be >>> than mixing across themConvection:•Air-sea cooling & evaporation creates cool & saline surface waters •These waters are then denser than those just beneath them and they sink•Annual & diurnal time scalesConvection & the Conveyor Belt•NADW production drives the conveyorThe AtmosphereWind Field: Drives upper layer flows of the major gyresNet Heat & Freshwater Exchanges: Drives buoyancy flows (like the conveyor belt) Convergence of trades leads to ITCZ:•Ascending moist air at equator•Drying & subsidence high pressure over the subtropical oceanLocation of ITCZ shifts seasonally•Driven in large degree by greater seasonal heating on the landWinds blow from high to low pressureEarth’s rotation  apparent force called the Coriolis force  turns the winds to the right (left) in the northern (southern) hemisphere.Mid-latitude storms do most of the atmospheric heat transportCyclones: low pressure & CCW (NH) rotationAnticyclones: high pressure & CW rotationEkman TransportWind stress (w)  input of momentum into the ocean by the wind•tw is a tangential force per unit area (N m-2 = kg m-1 s-2) Fridtjof Nansen (Pioneer in oceanography)•Nansen built the ship “Fram” to reach North Pole;•Lock ship in the ice & wait  set out to NP;•Nansen noticed that movement of the ice-locked ship was 20-40° to right of the wind•Nansen figured this was due to a steady balance of friction, wind stress & Coriolis forces•Ekman did the mathEkman TransportA ocean layer is accelerated by the one above it & slowed by the one beneath itTop layer is driven by tw  Transport of momentum into interior is inefficientTop layer balance of tw, friction & CoriolisLayer 2 dragged forward by layer 1 & behind by layer 3Depth of frictional influence defines the Ekman layerTypically 20 to 80 m thick Boundary layer process•Typical 1% of ocean depth (a 50 m Ekman layer over a 5000 m ocean)Ekman transport describes the direct wind-driven circulationOnly need to know tw & f (latitude)Ekman current will be right (left) of wind in the northern (southern) hemisphereSimple & robust diagnostic calculationInertia CurrentsEkman dynamics are for steady-state conditions if the wind stops  Coriolis will be the only forceInertial motions will rotate CW in NH & CCW in the SHImportant in open ocean as source of shear at base of mixed layer•A major driver of upper ocean mixing•Dominant current in the upper oceanPressureHydrostatic pressure  the weight of water acting on a unit area at depthTotal pressure = hydrostatic & atmospheric (pt = ph + pa)Hydrostatic pressure:•ph = g D•Links water properties () to pressure•Given (z), we can calculate ph•Rule of thumb: 1 db pressure ~ 1 m depthHorizontal Pressure GradientsPressure changes provide the push that drive ocean currents ;Geostrophy: •balance between horizontal pressure & Coriolis forces•Relationship is used to diagnose currents1. u = (g/f) tanwhere f = Coriolis parameter (= 2 sin)•Holds for most large scale motions in seaNeed to slope of sea surface to get at surface