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Coastal Oceanography (Fach) / Jacob (Lektion)

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• Why coastal conditions differ from open sea coast is boundary for flow shallow depth discharge river/rainfall Continental air masses
• why is coastal area so energetic Large tide height and stronger tide currents variation in S and T and sea level are more pronounced
• Why coastal ocean more important to humans mot fishing grouns in coastal areas sewage and effluent end in coast sport, recreation need knowledge for production of oil, renewable energy etc.
• a)coast b) beach c) shelf d)shelf break a) land mass adjacent to sea b) coast limits c)extent 1:500 (vertical:horizontal) d) 1:20 depth gradient
• Main effects of coast a) direction b) waves limit possible direction of movement - horizontal flow tends to be horizontal to along coast waves approaching shoaling region break, reflect, refract  (change height, velocity, distributoin of energy)
• Beach equilibrium and what can destroy regulated by local currents (tides) Breakwaters can lead to destruciton of equilibrium
• mixing in shallow waters limited due to shallow depth thus seasonal effect even stronger (temp, evaporation...)
• stratification a) b) and results a) caused by fresh water influx b) solar radiation lead to evaporation thus increase salinity =sharp halocline at surface bzw. sharp thermocline during summer »»no mixing »decrease in water quality
• Pyhsical properties salinity and river runoff a)river runoff a) fresh water on surface and if enough mixing on bottom high amount of SS (low optical trasnparency) »sometimes say on surface with low sal so bottom clear or sedimentation when increase salnity due to flocculation river runoff is seasonal  and has same seasonality with rain fall or glacier melting
• Fast Ice in high latitudes ice forms in coastal waters bc limited heat storage and low salinityy
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• salinity values a)normal ocean b) river influence c) red sea a) 34-35 (75%) b) sal 20 eg. 200km away from river mouth c) 40
• how is stability measured with stability parameter E: E>0 =stable
• Brunt Vaisala =influence of stratification if particle moved from equilibrium position and returns then acts like a spring if frequency high the water is very stratified , if frequency low it is not so stratified
• Richardson Number = Dynamic stability velocity change in stable environment can blead to instability if shear is lage enough eg. stable water surface is disturbed by wind and waves result =instability when Ri>0.25 stable , otherwise shear force induces turbulences  »»only work together with a large Reynolds number       »»normally both conditions only coe together in estuarine or coastal areas
• Kelvin Helmholzt instability 2 streams travel with different velocities and velocity shear causes instability
• Wind stress  horizontal friction force acting over sea surface and depends on wind speed, roughness of sea sruface and prevailing atmosphric conditions
• relation wind and sea surface and resulting phenomena momentum transfer from atmophere onto sea suface result in a) surface gravity waves (transfer of energy) b)surface current : transfer of mass (approx 3% of wind speed)
• Eddy viscosity friction coefficient of friction b/wwater parcels bc parcel viscosity is higher than molecular Az= vertical mixing Ah: horizontal mixing
• Ekmann theory wind blowing and drift current result due to coriolis force deflection of surface current to 45degress to the right. Buut layers below more and more deflicted thus net transport is 90degree to the right »»upwelling » velocity decreases exponentially »when v almost 0 the deflection is in opposite direction , normally at depth of 20-40m
• Converence and divergence D Due to wind blowing and the trasnport of mass convergence and divergence are the result convergence : downwelling (Ekman pumping) anticyclonic divergence: upwelling (ekman suction) cyclonic
• langmuir circulation small scale convergence resulting in elongated vortices which align with the wind »helical vortixes axes parallel to wind direction reuslt of instability on well mixed surface »induced by wind currents >7m/s and currents induced by waves =linear instability »difference b/w tubes 10s of meters »length horizontal km or 10s of km
• barotropic baroclinic isobars (pressure) parallel to isopicnics (density) Baroclinic - not praralell
• convergence/divergence coastal areas barotropic baroclinic offshore, where i have convergence <0barotropic condictions= barotropic jet but at coast have divergence and baroclinic condictions bc of isobars = baroclinic jet the slope decreases towards depth and becomes even = no geostrophic current and then moves the other direction inducing countercurrent
• currents induced by upwelling do to upweeling and thus horizontal pressure gradient a geostrophic flow ,, together with the 45degree surface flow result in a current towards equator
• how detect upwelling detect via surface temperature (sattelite or in situ) bc upward motion is very small (5-10m/day) or detect via rate surface layer moves offshore (ekman) = same as upwelled waters
• Upwelling Scales of Interest Distance of front to shore (cold water meets warm offshoer water) internal rossby deformation : width of interface b/w upper and lower water of upwelling front
• Kelvin Waves general definition =movement of high and low pressure centers along the coasr variability of currents (coastal areas) mainly caused by coastal trapped waves generation and propagation based on balance b/w forces of open ocean kelvin waves feature long period and small amplitude
• Geostrophic balance pressure gradient force perpendicular to flow and balanced by coriolis force in opposite direction inducing geostrophic current
• requirements kelvin waves need boundary to travel along like coast or shoreline or wide channel no wide shelf required
• kelvin waves equaton parameters check equation
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• kelvin waves _ how boundaries influnce the waves a)alongshore´ b)crossshore a)alongshore momentum balance (y): same as non dispersive waves b)crosshore momentum balance (x) : geostrophic: aomplitude decays exponentially from shore to open sea
• kelvin waves - main features (8 points) 1. Gravty driven 2. Non dispersive 3.result from abrubt change in wind field (eg shift of trade winds) 4.largest amplitdue at coast 5.amplitude decays exponentially towards offshore 6.West coast: only can propagate towards euquator 7.East coast: only propagates towards poles 8.Perdios: days over weeks - manifest thru slow water level changes or revearsal of inshore current
• kelvin waves at equator no coast to lean on and current cannot circulate aruond the center bc coriolis force act in opposite directions =»»reversed of geostrophic current if both side high pressure »» always travel eastward if both side low pressure »»move westward »higher speed than kelvin waves on coast but sme periodicity »wave guide is the equator
• how to detect kelvin waves variance in temperatures (periodic up and downwelling) sea level has same periodicity
• topography influence on coastal trapped waves bottom gradient of shelf results in waves When shelf is constant - waves only move in and out when shelf is sloping: water coloumn increases and narrows when go offshore >>due to conservation of momentum, the water colomn ctarts rotating when going offshore and slows down when moving inshor  >>offhore/inshore movement related to vorticity change  >>change of vortocity leads to particle propagation (wave propagation) in one direction  =Phaae propagation
• difference kelvin wave and coastal trapped waves coastal trapped waves do not decay towards offshore
• properties coastal trapped waves >travel towards ppoles on eastern side of ocean like kelvin waves > not existing on equator >similar periods and wavelength as kelvin waves >but different wave profile than kelvin waves  >maximum of oscillation over shelf edge >strongest currents at mid depth >currents and sea level change with season as stratification change with season  >big effect on sea level and currents on shelf
• Coastal Fronts a)definition b)width c) responsible for width d)maximum hydrographical property variance enhanced horizontal gradient of hydrographic properties, which vary rapidly =visible horizontal boundaries  b) ocean reach 100km, estuary few meters c) scale of process inducing front is responsible for size d) max variance right at middle of front and decreasing towards the sides
• 6 types of fronts 1. Ocean/Planetary front (deep ocean) 2.Upwelling front (Cpastal)  3.Shelf break front (coastal) 4.Shallow Sea Front (coastal)  5.Plume fronts (estuaries)  6.estuarine fronts (estuary)
• Common features all fronts 1) convergence flow, bringing waters together and resulting in vertical movement (vertical transfer of momentum) 2. regions of intense mixing and turbulences 3. High speed aand large velocity gradient 4. seen as barriers but intensive mixing along them  5: assimilation of nutrients and chem. species 
• a) Frontal zone b) Frontal axis c) Measure fronts a) region of rapid property change at surface  b) location of largest horizontal property gradient c)for horizontal can measure temp and salinity - for downward movement need eg. chla 
• classification of fronts 1. 2. 1. density fronts: density gradient maximum at front 2. density compensated: sal and temperature compensate density change and front cant be seen by density  >>usually not so distringuishable so clear - mix
• a) porperties density fronts b) properties density compensated fronts a) formation strong jet geostrophic current along front with eddy formation  >divided into prograde front: shelf water denser and isopicnic slope upwards towards coast                       retrogate: sheld water less dense and isopiccnals slope downward coast b) no enhance flow along the front     s trong layering and intrusion
• 1) Planetary fronts: Span of entire ocean basin associated with planetary wind system  impact global air/sea interaction  eg. subtropical front and subpolar oceanic gyres
• upwelling fronts =result of ekmann trnasport when the thermocline breaks and colder water is transported to surface >location follows strenghtening and weakening of the upwelling  >appears every 1-2 weeks like upwelling >convergence where water sinks at the frontal zone  >due to the front passive particles like plankton cannot drift of offshore >prograde fronst 
• shelf break fronts =front between coast and open sea 2 water masses meeting at shelf break but no intrusion of ocean water    >>moves along outer edge more or less stationary bc contrtoolled position of shelf break can be density or density copensated fronts width of front is baroclinic (Internal Rossby)
• shallow sea fronts =shallow regions with moderate to strong tidal currents >solar radiation induces stratification  >in some parts mixing very strong, in others stratification inhibits mixing >>Front >location of front predictable with heat input and tidal current input     >>highest heat input in summer , lowest in winter     >>tidal current weaker in deeper ocean and stringer with shallower depth  >studied by simpson and james: developed stratification index : front s= 2.7  (not well understood phenomene)
• Plume fronts fresh water reaching estuary or ocean >strong convergence and turbulence leading to accumulation of drifting material and foam
• estuarine fronts =miniature shallow sea front >difference: stability more defined by salinity, not temperature  >not destricted to mouth of estuary >run parallel to estuarine banks >upper layer fresh, lower layer salt  = stratification >>broken in more shallower depths 
• a) Definition estuary b) and classification types a) semi enclosed coastal body, connection to open sea, extending into river as far as limit of tidal influence, within diluted sea water measureable  b) 1) Beased on freshwater balance      2) based on tides      3)based on geomorphology       4) based on mixing processes 

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