Download Oceanography Lecture 12

Because,
OF ALL
THE ICE!!!
How do you
know there’s
an Ice Age?
Global Circulation Patterns:
3) Atmosphere-Ocean “coupling”
Low latitudes: Oceans
High latitudes: Atmosphere
Oceanography
Lecture 12
i. The Ocean/Atmosphere coupling
ii.Surface Ocean Circulation
Atmosphere-Ocean “coupling”
Atmosphere – Transfer of moisture to the
atmosphere (heat released in higher latitudes
as water condenses!)
Atmosphere-Ocean “coupling”
Atmosphere – Transfer of moisture to
the atmosphere: Hurricanes!
In summary
Latitudinal Differences in Energy
www.weather.com
Amount of solar radiation received annually at the Earth’s surface
Latitudinal Differences in Salinity
Latitudinal Differences in Density Structure of the Oceans
Heavy
Light
T has a much greater
impact than S on
Density!
Atmospheric – Wind patterns
January
Atmospheric – Wind patterns
January
Westerlies
Easterlies
Easterlies
Westerlies
High/Low Pressure systems: Heat capacity!
High/Low Pressure systems: Wind generation
Wind drag
Zonal Wind Flow
Wind is moving air
Air molecules drag water molecules
across sea surface (remember waves generation?):
frictional drag
Westerlies
If winds are prolonged, the frictional drag generates a
current
Easterlies
Only a small fraction of the wind energy is transferred to
the water surface
Easterlies
Westerlies
Any wind blowing in a regular pattern?
High/Low Pressure systems: Wind generation by flow from
High to Low pressure systems (+ Coriolis effect)
1) Ekman Spiral
Once the surface film of water molecules is set in motion, they exert a
frictional drag on the water molecules immediately beneath them,
getting these to move as well.
Motion is transferred downward into the water column
! Speed diminishes with depth (friction)
! Direction changes with depth (coriolis)
1) Ekman Spiral
Spiraling current in which speed and direction change with
depth:
Net transport (average of all transport) is 90° to right
(North Hemisphere) or left (Southern Hemisphere) of the
generating wind.
Transport occurs at most down to 100m!
1) Ekman Transport
An example:
July
1) Ekman Transport
An example:
January
1) Ekman Transport
Surface circulation
Large central “gyres” in ocean basins
2) Geostrophic Flow
Ekman transport is limited to ~100m!
How come the Gulf Stream extends down to 500-800m?.
Pressure or geostrophic gradients (P = ! gh)
1)
2) Geostrophic Flow
Dynamic equilibrium between Coriolis deflection and
pressure gradient
2)
2) Geostrophic Flow
Western intensification due to transport and vorticity
3)
Ekman Transport
1) Downwelling:
Convergence zones generate downwelling of water and nutrients
The Gulf Stream
Western intensification
Grand scheme of things…
Surface circulation: Heat transport
Ekman Transport
2) Upwelling:
If wind blows parallel to a shore in the proper direction
Ekman
transport moves near-surface water offshore. Water must then
rise from below to compensate for seaward surface flow.
1) Ekman Transport
Upwelling: Peru; California; Africa; Australia
Grand scheme of things…
Surface circulation: Warm and cold currents
Balance of Earth Heat budget