Download convection in the atmosphere and oceans

AOS 101 Weather and Climate
Lisha M. Roubert
University of Wisconsin-Madison
Department of Atmospheric & Oceanic Sciences
Differences between the Atmosphere
and Oceans

1.
Forcing in the oceans is different from forcing in the
atmosphere.
Heating destabilizes the atmosphere and
stabilizes the ocean.
 In
the atmosphere: the sun heats the surface, which
transfers heat and causes air it to rise.
 In the ocean: when the surface of the ocean is heated
nothing happens
2.
Buoyancy forcing is important as well.
Buoyancy



Buoyancy is an upward acting
force that opposes an object's
weight.
This force is caused by fluid
pressure.
If the object is either less dense
than the liquid or is shaped
appropriately (as in a boat),
the force can keep the object
afloat.
Structure of the Ocean



The oceans is stratified into layers of water of different density. The less
dense water will be at the surface and the density increases with depth.
Density in the ocean is determined by salinity and temperature.
 Warm and less salty=lower density
 Cold and very salty=higher density
Density is a measure of Buoyancy. Water masses with less density will be
more buoyant.
Profile of how Temperature, Salinity
and Density change with Depth
Convection in the Oceans

Convection in the oceans varies
with seasons.


In warm months: the sun warms
the upper layer of the ocean and
keeps it well mixed so that we
have warm water at the surface
of the ocean and cold water at
the bottom. Not much convection.
In cold months: cold wind blows
over the surface. This cools the
water at the surface of the ocean
and make it more dense causing
it to sink deeper. This causes
deep convection.
Normal Ocean in Summer
heat
warm
cold
Shallow
convection
Mixed Layers



Buoyancy and stratification determine mixing.
The thermocline is the transition layer between
the mixed layer at the surface and the deep
water layer.
The definitions of these layers are based on
temperature.



mixed layer- it is near the surface where the
temperature is roughly that of surface water.
thermocline-transition zone between mixed
layer and deep water. The temperature
decreases rapidly from the mixed layer to the
deep water
Deep water-water at the bottom with very cold
temperatures
Differences between convection in the
atmosphere and oceans



ATMOSPHERE
Convection propagates upward
into the atmosphere.
In warm months there is more
convection. The ground is
heated. This heat is transferred
to the air, the air will get warm
and rise and cold air descends
to replace the air that
ascended.
In cold months the air at the
surface will be very cold and
will not rise as much which
indicates less convection.



OCEAN
Convection propagates
downward into the ocean.
In warm months there is
less convection. The water
is heated but the heated
water will not reach great
depths.
In cold months we have
deep convection because
water at the surface
becomes more dense (less
buoyant) and thus sinks.
Today in the Lab



Satellites can only take
measurements at the surface
of the ocean, that’s why we
need probes instead to take
measurements at a much
greater depth.
The data you will be using
today was taken from an
XCTD probe.
XCTD probes take
measurements of
temperature, salinity,
conductivity, density at
different depths. (In our case
from 2m-999m)