Ocean Circulation 2 - Dr Davis Evans

Question 1

describe the Coriolis effect

Answer 1

At the equator the earth rotates at ~1000 miles/hour. At 60 deg latitude the velocity is ~500 miles/hours. An object fired northwards from the equator will initially retain the eastward velocity of ~1000 miles hour so will veer to the right as it travels northwards. In the southern hemisphere, an object fired from the equator southwards will veer to the left.

The Coriolis effect is maximum at the poles and zero at the equator

Question 2

main gyre rotations

Answer 2

clockwise in the northernhemisphere

anticlockwise in the southern hemisphere

Question 3

Coriolis effect deflect which direstion in the north and south?

Answer 3

Right in the north

Left in the south

Question 4

how was the Coriolis ffect first observed?

Answer 4

Nansen - a Norwegian explorer observed that ice did not travel parallel to wind, but 20-40 degrees to the right of it

Question 5

Ekman’s model

Answer 5

Ekman transport should be at 90 degrees to right of wind (in N Hemisphere)

The mathematical formulation of the Ekman layer can be found by assuming a neutrally stratified fluid, with horizontal momentum in balance between the forces of PRESSURE GRADIENT, CORIOLIS and TURBULENT DRAG.

in reality movement is less than this. The entire layer that moves is the Ekman layer (usually < 100 m deep). In shallow water (<100m), friction with the bottom dominates and the water tends to move with the direction of the wind.

Question 6

domes?

Answer 6

Ekman transport tends to pile water up in te centre of ocean gyres
this sinks, compressing the layers beneath

forcing those layers to spread, pushing the thermocline deeper

Question 7

geostrophic current

Answer 7

. When the Coriolis and horizontal pressure gradients balance, the system is geostrophic equilibrium and the current is a geostrophic current

Question 8

Horizontal pressure gradients?

Answer 8

due to the hill of water formed at the centre of a gyre, the water will want to move from the centre (high pressure)to the outside (lower pressure)

Question 9

asymmetry of the gyres

Answer 9

Westward intensification creates fast, deep, narrow western boundary currents and shallow, slow, wide eastern boundary currents.

Question 10

Counter currents

Answer 10

Equatorial counter currents occur in all oceans (Atlantic, Pacific and Indian). The trade winds blow from the north east in the Northern hemisphere and from the south east in the Southern hemisphere. This creates a sea surface slope, higher in the west and lower in the east. The slope creates a horizontal pressure gradient from from the west to the east which results in the counter current. Close to the equator, the Coriolis affect is small but in the Atlantic the counter current is in the northern hemisphere and is diverted slightly to the right (towards the equator).

Question 11

Antarctic divergence

Answer 11

The East Wind Drift (wind at the continent) causes the Antarctic coastal current to flow westwards. The westerly West wind drift promotes the clockwise Antarctic Circumpolar current. In the Southern hemisphere the Coriolis acts to the left so the Antarctic coastal current tends to be diverted south towards Antarctic while the Antarctic Circumpolar Current is diverted northwards.

Question 12

Antarctic convergence

Answer 12

1. Upwelled NADW moves north at the sea surface (it’s now called Antarctic surface water, AASW)
2. At the convergence, AASW (Antarctic water) meets Sub Antarctic water (which is much warmer)
3. The AASW (Antarctic surface water) sinks to form Antarctic Intermediate Water (AAIW)

this causes vertical circulation