Download EPSS 15 Spring 2017 Introduction to Oceanography Atmospheric

5/12/17
EPSS 15 Spring 2017
Introduction to Oceanography
Laboratory #6
Ocean and Atmosphere Circulation
Atmospheric Circulation
•  The amount of
heat per unit
area at the
equator is
greater than at
higher latitudes.
•  This creates a
heat differential/
imbalance.
•  The winds are
generated to
restore
equilibrium.
1
5/12/17
If the Earth did
not rotate we
would observe
a single
circulation cell
in each
hemisphere
that would
bring hot air
from the
equator to the
cooler polar
regions.
Warm air
rises
near the
Equator
and
travels
toward
the poles
This is deflected by the Coriolis effect and sinks at 30°
where it flows as surface winds toward the Equator
(Trade winds) and toward 60°(Westerlies)
2
5/12/17
Ocean Circulation
•  Surface currents
- driven by winds
•  Deep ocean circulation
- caused by buoyancy forces
(temperature and salinity
differences; driving force is gravity)
Ekman Transport
Winds push the ocean surface and set it in motion, but due
to the Coriolis effect transport is deflected. Deflection is to
the right in the northern hemisphere and left in the
southern hemisphere. Under ideal conditions, the
surface layer is deflected 45°and net transport is 90°.
3
5/12/17
Ocean Circulation
•  Surface circulation
is driven by the
winds. Transport is
deflected by the
Coriolis effect and
by continents
forming the
subtropical gyres.
These subtropical
gyres are the main
component of
surface circulation
North
subtropical
gyre
South
subtropical
gyre
Subtropical Gyres
There are five subtropical gyres; each has
four component currents
4
5/12/17
Subtropical Gyres have four components:
1.  Equatorial Current - driven by Tradewinds
2.  Western Boundary Current (HOT) - deflected by Coriolis
and continents
3.  West wind drift - driven by Westerlies
4.  Eastern Boundary Current (COLD) - deflected by
Coriolis and continents
Eastern
BC
Western
BC
Deep Currents
•  Driven by buoyancy (density) forces - Gravity is
the driving force.
•  Referred to as thermohaline circulation:
- thermo=heat, haline=salt.
•  Both of these affect density.
•  Flow is much slower than surface currents: ~1000
years for deep water to circulate.
•  Formation of deep water is primarily due to
evaporation and the formation of sea ice:
- both these processes make the water more
dense and thus sink to the bottom.
5
5/12/17
NADW - North Atlantic Deep Water
–  forms near Greenland; evaporation and cooling causes
surface water to sink and flow south
AABW - Antarctic Bottom Water
–  Densest deep water
–  Cold, dense water from sea ice formation in the Weddell
Sea sinks and mixes with NADW to form AABW
Young deep
water here
mixing
here
Old deep
water here
Deep Currents
6
5/12/17
Oceans have a stable density stratification, with
less dense layers over deeper, more dense layers
Pycnocline is a
region of rapid
density change,
caused by steep
gradients in
temperature and
salinity
Water masses can be distinguished by
their temperatures and salinities
7
5/12/17
EPSS 15 Fluid Dynamics Demo
8
5/12/17
9
5/12/17
10
5/12/17
11