First 4 lectures init

Question 1

Description of Upper Mixed Layer

Answer 1

• Layer at surface of ocean of ocean driven by winds and possibly convection via T & S fluxes
• Turbulence is present which homogenises momentum, temperature and salinity
• Thickness 10-200m depending on stratification & season
• Directly below is permanent thermocline
• Thermocline stretches from 300-1000m and is steep T gradient
• A seasonal thermocline may also be present

Question 2

Physical Description of Ekman layer

Answer 2

• Layer at top of ocean directly influenced by wind stress
• Ocean currents at the surface are 45 to the wind direction (R in N hemi)
• Ekman spiral where magnitudes of currents decay exponentially and at increasing angle to wind with depth
• Vertically intergrated transport perpendicular to wind stress direction
• Balance between coriolis and vertical viscous effects (coriolis, drag, wind)
• 50-300m depth

Question 3

Why is there Ekman Pumping at the equator?

Answer 3

Sign of coriolis changes across the equator resulting in divergence of surface currents resulting from trade winds.

Question 4

What are the units of flux?

Answer 4

Q = X m-2 s-1   e.g. J m-2 s-1
Q = Qm-2 (Watts per m squared)

Question 5

What is an f-plane approximation?

When is it used?

Answer 5

Assume Coriolis force is constant

Describing flow in small regions relative to the radius of earth but larger than few 10s km

Question 6

What is an beta-plane approximation?

When is it used?

Answer 6

For larger domains than f-plane where Coriolis assumed to vary linearly with latitude

Question 7

What are the major aspects of circulation in N. Atlantic

Answer 7

• Basin scale sub-tropical and sub-polar gyres
• WBC, the gulf stream
• Gulf stream recirculation due to baroclinic instability (2-3x mass transport as larger gyre)
• Equatorial current and counter-currents
• Strong cross equatorial flow in West

Question 8

What behaviour do we expect for large reynolds numbers?

Answer 8

Turbulent behavior

Question 9

What is turbulent behavior

Answer 9

• Property of fluid flow
• Irregular and unpredictable advection of interacting vortices
• on varying temporal and spatial scales
• where small perturbations can grow rapidly
• Leads to enhanced mixing of momentum

Question 10

Describe the four principal processes that influence freshwater fluxes

Answer 10

• Evap
• Ppt
• River runoff
• Ice freeze/melt

Question 11

List four components of heat flux in order of their relative magnitudes close to the equator

Answer 11

Shortwave (insolation)
Latent
Longwave
Sensible

Question 12

Describe the concept of eddy diffusivity

Answer 12

-Large Reynolds no
- Turbulent Behaviour
- Leads to enhanced mixing of momentum
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