Coastal Ocean Dynamics
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Coastal Ocean Dynamics Second course: North Sea dynamics. Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde [email protected] North Sea bathymetry. Source: Werner Alpers. North Sea catchment areas and Exclusive Economic Zones. Weser. Elbe.

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Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde

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Hans burchard leibniz institute for baltic sea research warnem nde

Coastal Ocean Dynamics

Secondcourse:

North Sea dynamics

Hans Burchard

Leibniz Institute for

Baltic Sea Research Warnemünde

[email protected]


Hans burchard leibniz institute for baltic sea research warnem nde

North Sea

bathymetry

Source: Werner Alpers


Hans burchard leibniz institute for baltic sea research warnem nde

North Sea

catchmentareas

and

ExclusiveEconomicZones

Weser

Elbe

Rhine

Source: OSPAR Commission


Hans burchard leibniz institute for baltic sea research warnem nde

Annual cycleofseasurfacetemperature in North Sea


Hans burchard leibniz institute for baltic sea research warnem nde

Generation ofthe semi-diurnal lunar (M2) tide

http://www2.astro.psu.edu/users/cpalma/astro10/class21.html


Hans burchard leibniz institute for baltic sea research warnem nde

Generation ofthe semi-diurnal solar (S2) tide

http://www2.astro.psu.edu/users/cpalma/astro10/class21.html


Hans burchard leibniz institute for baltic sea research warnem nde

Tidalchartforthe M2tide (phaselines)

http://en.wikipedia.org/wiki/Amphidromic_point


Hans burchard leibniz institute for baltic sea research warnem nde

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.


Hans burchard leibniz institute for baltic sea research warnem nde

Tidalchart

forthe M2tide

fulllines: amplitude

dashed: phase

(Source: POL)


Hans burchard leibniz institute for baltic sea research warnem nde

Tidalchartforthe M2tide (phaselines)


Hans burchard leibniz institute for baltic sea research warnem nde

Amphidromicpoint

M2tidalchartof Southern North Sea

Prandle, 1981


Hans burchard leibniz institute for baltic sea research warnem nde

Tidalpropagationintothe Baltic Seaisblocked !


Hans burchard leibniz institute for baltic sea research warnem nde

Tides in theWaddenSea (asseen in 200 m resolution model)


Hans burchard leibniz institute for baltic sea research warnem nde

WaddenSea model:

M4tidalelevations

(phaseandamplitude)

asvalidationdata.

Gräwe et al., in prep.


Hans burchard leibniz institute for baltic sea research warnem nde

Seasonalityoftidalforcing

Howdoesthisaffect

sedimenttransport

due totidalasymmetries (M4)?

Gräwe et al. (in prep.)

Müller et al. (in prep.)


Hans burchard leibniz institute for baltic sea research warnem nde

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)


Hans burchard leibniz institute for baltic sea research warnem nde

Stratificationisspatially not homogeneous

Tidal front

Doggerbank

Doggerbank

Model resultsby Burchard & Bolding, 2002


Hans burchard leibniz institute for baltic sea research warnem nde

Tidalfronts

Tidalfronts(stratified in deep, mixed in shallowwater) are an environmentallyveryimportantphenomenon.

Thus, in shallowwaterthebottomsedimentis in directcontactwiththesurfacewaters, whereas in deeperwaters, thebottomlayersareclearlyseparatedfromthesurfacewates.


Hans burchard leibniz institute for baltic sea research warnem nde

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

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 sea1

Tidal Mixing fronts in the Irish Sea

Stratification Simpson-Hunter parameter

Numerical model result, Souza et al., in press.


Hans burchard leibniz institute for baltic sea research warnem nde

Environmental effectsofseasonalthermal stratification

Surfaceheatflux (cumulated)

during FLEX‘76

Burchard, 2002


Hans burchard leibniz institute for baltic sea research warnem nde

FLEX 1976

Lateral effects

aresmall, such that

one-dimensional

modellingmaybe

successful

Burchard, 2002


Hans burchard leibniz institute for baltic sea research warnem nde

Summer stratificationalong 56°North Seatransect


Hans burchard leibniz institute for baltic sea research warnem nde

Summer chlorophyllconc. along 56°North Seatransect


Hans burchard leibniz institute for baltic sea research warnem nde

Northern North Sea:

Annual cycleof

stratificationand

primaryproduction

Burchard et al., 2005

Burchard, 2002


Hans burchard leibniz institute for baltic sea research warnem nde

Rotatingbulkshear in Monterey Bay

Itsweire et al. (1989)


Hans burchard leibniz institute for baltic sea research warnem nde

PROVESS-NNS study site

(observations: Sep-Nov 1998)

Wind

ADCP, CTD, MST


Hans burchard leibniz institute for baltic sea research warnem nde

Bulk property observations in NNS

Wind

Bulk shear squared

Bulk shear direction

vs.

inertial rotation


Hans burchard leibniz institute for baltic sea research warnem nde

Theory I

1D dynamic equations:

Layer averaging:


Hans burchard leibniz institute for baltic sea research warnem nde

Dynamic equationforbulkshearsquared:

Conclusion:

Assumingbed stress beingsmall, bulkshearisgenerated

bythealignmentof wind vectorandshearvector.


Hans burchard leibniz institute for baltic sea research warnem nde

Application of

theory to

observations


Hans burchard leibniz institute for baltic sea research warnem nde

Impact of

bulk shear on

diapycnal mixing

Conclusion:

Increased interfacial

mixing rates correlate

with high shear.

Can we resolve this

in 3D models?


Hans burchard leibniz institute for baltic sea research warnem nde

Transect in NNS

Observations (Scanfish data from BSH)

Model results (GETM with adaptive coordinates)

Gräwe et al. (in prep.)


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