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EAS 212: The Oceans > 8. Ekmann Upwelling etc > Flashcards

8. Ekmann Upwelling etc Flashcards

1
Q

Wind-driven circulation happens in the upper __-__m of the ocean

A

500-1000m

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2
Q

Winds generate movement in the ocean in 2 ways:

A
  1. by transferring its energy to the surface water through friction
  2. by blowing/ pushing the surface waters in a given direction, creating a slope on the sea sfc –> pressure gradient
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3
Q

wind energy transfer (via ____) generates currents and waves

A

friction

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4
Q
A
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5
Q

Generally, about __-__% of the wind energy is converted to ocean kinetic energy

For example, 60km/hr winds give __-__km/hr ocean currents

A

1-3%

1-2km/hr

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6
Q

T/F

Ocean speed generally decreases with depth

A

true

b/c as subsequent layers interact, only a fraction of the kinetic energy is transferred down

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7
Q

____ observed that the surface layer of the ocean is deflected __-__ degrees to the right of the wind

____ developed the circulation model to explain this observation

A

Nansen
20-40

Ekman

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8
Q

Ekman spiral states:

A

The surface current will deflect 45 degrees
(to the right in NH and left in SH).

The deflection increases as you go deeper (at a certain depth, current can go opposite direction of the wind)

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9
Q

In practice, does the surface current deflect exactly 45 degrees via Ekman?

A

No, it’s usually less than 45 degrees

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10
Q

What’s the total transport of water when you average all the currents (at different depths)?

A

The total transport of water is 90 degrees

(to the right in NH and left in SH)

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11
Q

Give 3 conditions that must hold true for the Ekman motion to be set up

A
  1. the water column must be nearly uniform in density over the spiral
  2. the winds must blow at a constant speed for at least 1-2 days
  3. if the water is too shallow, friction with the bottom stops the establishment of the ekman spiral
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12
Q

T/F

Interactions with the bottom (friction) set up another ekman spiral at the bottom of the oceans

A

true!

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13
Q

Explain how winds can drive vertical movement of water in the ocean

A
  • When winds blow away from an area, they cause divergence, which lets water UPWELL from below (cold water from below the pycnocline)
  • When winds blow towards an area (eg landmass), = convergence of ocean currents= downwelling
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14
Q

Explain how ekman can cause upwelling

A

If the offshore winds are parallel to the shore, the resulting water movement is either outward or inwards, depending on wind direction (deflection to right in NH). Water then upwells or downwells to fill that space

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15
Q

Give 3 causes of upwelling/ downwelling

A
  • offshore winds
  • seafloor obstructions
  • sharp bends in coastlines
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16
Q

t/f

downwelling areas have high productivity

A

false

low

17
Q

Why might the mean flow in deeper layers oppose the Ekman transport?

A

Pressure gradient transfer!

18
Q

Flows are accelerated and deflected until the pressure gradient is balanced by the ________ ______. This is called a _______ _______

A

Coriolis force

Geostrophic current

19
Q

Geostrophic currents are __ degrees to the ___of the pressure gradient in the northern hemisphere

A

90

right

20
Q

Ideally, geostrophic currents flow parallel to the ___

A

isobars

21
Q

In the open ocean, surface currents are initiated by ___ ___, and then maintained as ______ _______

A

Ekman transport

Geostrophic currents

22
Q

The larger the pressure gradient, the ___ the geostrophic current

A

larger

23
Q

What is the typical ocean unit of volume transport?

Equivalent to:

A

Sverdrup (Sv)

1Sv= 10^6m^3/sec

24
Q

Ekman transport is based on the large-scale ____ circulation

This leads to a band of convergence at __ degrees and divergence at __ degrees. What does this create?

A

atmospheric

convergence= 30 degrees
divergence= 60 degrees

Large-scale geostrophic currents that flow around the earth

25
Q

Gyre=

A

closed circulation loop within the ocean

26
Q

Only 1 current can flow all the way around the world, unobstructed by land:

A

Antarctic Circumpolar Current

27
Q

Do gyres spin at a constant speed?

A

Nearly constant, yes

It reflects the average wind input to the gyre

Doesn’t stop

28
Q

Subtropical gyres have a ____(lowered/raised) sea surface height in the middle. Why?

A

raised

Coriolis deflection of boundary currents towards the center + ekman transport to right (NH)= subtropical convergence of water in the middle of the gyre
- balanced by PGF pointed outwards

29
Q

Do subpolar gyres have a raised or depressed sea surface height in the middle?

A

depressed

30
Q

Sea surface height maximum appears shifted to the ___(east/west) side of subtropical gyres

A

west

31
Q
A

EAS 212: The Oceans (18 decks)

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