GEF2610 Physical Oceanography

GEF2610 Physical Oceanography

Course contentThe physical structure and circulations of the oceans, and the physical processes influencing them.

Learning outcomesThe students shall have knowledge about the physical properties of ocean waters, understand concepts like stability and potential density, and be able to describe the energy exchange with the atmosphere. They shall know how the standard instruments are functioning and understand the meaning of observations presented in a T-S diagram. The students shall have a good overview of the general oceanic circulation, understand the driving forces and mechanisms behind the different types of circulation, and know where in the world oceans bottom water is formed and where upwelling occurs.

• Ocean dimensions and extensions• Physical properties of ocean water • Chemical components of ocean water• Standard instruments• Forces; Equation of Motion• Energy exchange with the atmosphere • Physical structure of the oceans• General oceanic circulation • Waves• Tides

Ocean dimensions and extensions

• Names of the different oceans

• Topography of the different oceans

Sand waves

Relative dimensions of atmosphere and oceans

Physical properties of ocean waters

• Temperature, salinity, density• Compressibility• Potential temperature and density• Freezing point • Specific heat (heat capacity)• Latent heat of evaporation• Latent heat of freezing• Optical properties • Acoustical properties

Translational motion in gases

Light in the sea

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Snell’s Law of Refraction

Vertical attenuation

Fig. 3.9 Optical pathways to an ocean color sensor (from Robinson, 1983).

Fig. 3.10 Global chlorophyll concentration in mg/m3 for the ocean and Normalized Difference Vegetation Index (-1 to +1) for the land surface for Sept. 97 – Aug. 98.

Sound in the seaSnell’s Law of Refraction

Spherical attenuation

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Chemical composition of ocean water

• Principal constituents• Constant relative composition of seawater• Gases in seawater (O2)• Methods for determination of salinity• Methods for determination of density

Standard instruments

• Reversing thermometers• Water samplers (e.g. NIO bottles)• ST electronic bridges• CTD sensors• Irradiance meters• Secchi disk• Echo sounders• Current meters

Equation of Motion

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Simplified models

•Hydrostatic equilibrium

•Geostrophic current

•Ekman spiral

•Equilibrium tide

Hydrostatic equilibrium – hydrostatic pressure

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Geostrophic current

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Ocean dynamic topography

Tuva

Ekman spiral – wind current

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Wind speed

Equilibrium tide

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Energy exchange with the atmosphere

• Kinetic energy (currents, waves)

• Radiative energy (shortwave, longwave)

• Heat exchange (latent heat of evaporation, latent heat of freezing, heat conduction)

Budgets

• Heat budgets

• Volume budgets

• Salt budgets

• Knudsen’s Relations

General oceanic circulation

• Surface currents• Interaction between atmospheric wind and

pressure systems and the major oceanic gyres• Estuarine circulation• Upwelling• El Niño (ENSO)• Thermohaline circulation• Vertical convection• Bottom and deep-water formation

Polarfront

Estuaries

• Estuaries

• Fjords

• Estuarine circulation

• Deep water exchange in fjords

Front: brackish water / sea water

Gåsøyrenna: T and S 04.04.2008

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Gåsøyrenna: Density 04.04.2008

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Global distribution of temperature, salinity, and density

• Relationship between temperature, salinity and the large-scale pressure and wind systems at the surface

• Typical vertical profiles at low, middle and high latitudes

Waves

Wind waves

Wave height depends on:• speed (the force of the wind);• duration (the time the wind has been blowing); • fetch (the length of the area the wind is blowing

over).

Significant wave height : the average height of the highest third of the waves.

Wave height definition for a regular wave

Wave height definition for an irregular sea surface

Histogram of wave heights

Wave speed (phase velocity)

• Short waves (deep water waves)

• Long waves (shallow water waves) including tsunamies and tides

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Wave height

Storm

Typhoon Wipha

Earth – Moon Orbit

Tides

• Equilibrium tide (spring and neap tide, diurnal inequality)

• Real tides in the ocean

M2 amplitude

Bay of Fundy; High Tide

Bay of Fundy; Low Tide

Saltstraumen; mean speed 4-5 m/s, max speed 10 m/s?

Ice in the sea

• Slush, grease ice

• Pancake ice

• Pack ice

• Hummocs

• Icebergs

Grease and pancake ice

Pancake ice

Pack ice

Iceberg

Iceberg

GLACIER