gef2610 physical oceanography
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GEF2610 Physical Oceanography. Course content The physical structure and circulations of the oceans, and the physical processes influencing them. Learning outcomes - PowerPoint PPT PresentationTRANSCRIPT
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
ji sin3
4sin
zKeEzE 0)(
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
ji v
j
v
i sinsin
)(
2
2
00
0)( RRceR
RR
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
TgFcba
Simplified models
•Hydrostatic equilibrium
•Geostrophic current
•Ekman spiral
•Equilibrium tide
Hydrostatic equilibrium – hydrostatic pressure
gb
0
h
hgpdzzghp0
)0()()(
Geostrophic current
gcb
0
)tan(f
gv
Ocean dynamic topography
Tuva
Ekman spiral – wind current
Fc
0
Wind speed
Equilibrium tide
Tgb
0
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
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30 35
salinityD
ep
th
S-Gaasoy
S-Gaasoy-feb
T-Gaasoy
T-Gaasoy-feb
Gåsøyrenna: Density 04.04.2008
0
10
20
30
40
50
60
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19 20 21 22 23 24 25 26
Density - 1000D
ep
th Gaasoy
Gaasoy-feb
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
TsmLsmLg
c 215.0 56.125.12
hsmhgc 15.015.3
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