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Coastal Ocean Dynamics Second course: North Sea dynamics. Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde hans.burchard@io-warnemuende.de. North Sea bathymetry. Source: Werner Alpers. North Sea catchment areas and Exclusive Economic Zones. Weser. Elbe.
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Coastal Ocean Dynamics Secondcourse: North Sea dynamics Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde hans.burchard@io-warnemuende.de
North Sea bathymetry Source: Werner Alpers
North Sea catchmentareas and ExclusiveEconomicZones Weser Elbe Rhine Source: OSPAR Commission
Generation ofthe semi-diurnal lunar (M2) tide http://www2.astro.psu.edu/users/cpalma/astro10/class21.html
Generation ofthe semi-diurnal solar (S2) tide http://www2.astro.psu.edu/users/cpalma/astro10/class21.html
Tidalchartforthe M2tide (phaselines) http://en.wikipedia.org/wiki/Amphidromic_point
Why do thetides in the North Sealooklikethis ? Tidalwavesenterinto North Seathrough northern boundaryand English Channel. Phase propagationis c = (g * depth)1/2, g = 9.81 m/s2 (depth = 40 m c = 20 m/s = 72 km/h) Due to Earth rotation, tidalwavesare Kelvin waves, leaning on a coasttotheright. Energyloss due tobedfriction: tidalwavesloose power duringtheirjourneythroughthe North Sea.
Tidalchart forthe M2tide fulllines: amplitude dashed: phase (Source: POL)
Amphidromicpoint M2tidalchartof Southern North Sea Prandle, 1981
WaddenSea model: M4tidalelevations (phaseandamplitude) asvalidationdata. Gräwe et al., in prep.
Seasonalityoftidalforcing Howdoesthisaffect sedimenttransport due totidalasymmetries (M4)? Gräwe et al. (in prep.) Müller et al. (in prep.)
Stratification in the North SeaBesides tides, seasonal stratification is characteristic for the North Sea dynamics. Annual cycleoftemprature stratification in the Northern North Sea (asseenfrom a 1D model) Boldingand Burchard (2002)
Stratificationisspatially not homogeneous Tidal front Doggerbank Doggerbank Model resultsby Burchard & Bolding, 2002
Tidalfronts Tidalfronts(stratified in deep, mixed in shallowwater) are an environmentallyveryimportantphenomenon. Thus, in shallowwaterthebottomsedimentis in directcontactwiththesurfacewaters, whereas in deeperwaters, thebottomlayersareclearlyseparatedfromthesurfacewates.
Whatdeterminesthepositionoftidalfronts ? Stabilising: waterdepthH, surfacebuoyancyfluxQ (heatflux, netprecipitation). Destabilising: tidesgivenastidalvelocityamplitudeu. Importantparameterby dimensional analysis: (Q * H) / u3 Large:stablystratified; Small:mixed Note: H / u3isthefamous Simpson-Hunter (1974) parameter.
Tidal mixing fronts in the Irish Sea stratified & deep mixed & shallow mixed & very shallow & warm or stratified due to river run-off Satellite images courtesy Alejandro Souza
Tidal Mixing fronts in the Irish Sea Stratification Simpson-Hunter parameter Numerical model result, Souza et al., in press.
Environmental effectsofseasonalthermal stratification Surfaceheatflux (cumulated) during FLEX‘76 Burchard, 2002
FLEX 1976 Lateral effects aresmall, such that one-dimensional modellingmaybe successful Burchard, 2002
Northern North Sea: Annual cycleof stratificationand primaryproduction Burchard et al., 2005 Burchard, 2002
Rotatingbulkshear in Monterey Bay Itsweire et al. (1989)
PROVESS-NNS study site (observations: Sep-Nov 1998) Wind ADCP, CTD, MST
Bulk property observations in NNS Wind Bulk shear squared Bulk shear direction vs. inertial rotation
Theory I 1D dynamic equations: Layer averaging:
Dynamic equationforbulkshearsquared: Conclusion: Assumingbed stress beingsmall, bulkshearisgenerated bythealignmentof wind vectorandshearvector.
Application of theory to observations
Impact of bulk shear on diapycnal mixing Conclusion: Increased interfacial mixing rates correlate with high shear. Can we resolve this in 3D models?
Transect in NNS Observations (Scanfish data from BSH) Model results (GETM with adaptive coordinates) Gräwe et al. (in prep.)