Assignment #5
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Texas A&M University *
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Course
608
Subject
Geography
Date
Dec 6, 2023
Type
docx
Pages
3
Uploaded by MagistrateOtterMaster1954
Assignment #5
OCNG 608
3/1/18
5.1) Sketch
∂v
∂ z
>
0,
∂v
∂ z
<
0,
∧
∂v
∂z
=
0
in y-z space. What are the implications for vertical exchange
if Ri > 0, if Ri < 0 and if Ri > 0 but small, respectively?
If the Richardson Number (Ri) is less than zero then the water column is statically unstable. For the
Richardson Number to be less than zero, E would be less than zero and vertical exchange would occur. If
Ri > 0, E>0 and it would be statically stable with no vertical exchange. If Ri > 0 but very small then E > 0
and the water column would be statically stable but the velocity shear would be large, and it would have
dynamic instability. The velocity shear creates turbulence and the turbulence mixes the water leading to
vertical eddy viscosity and diffusivity.
5.2) What is convection all about? Where and what type of convection do we find in the ocean? How
is it triggered? What are the typical horizontal scales involved?
Convection happens when surface water is denser than the water underneath it. The water then mixes
downward. Convection occurs in the ocean because of the different density of ocean water either caused
by differences in temperature or salinity.
There are two types of convention in the ocean, open ocean convection and near boundary convection.
Open ocean convection occurs in the middle of the ocean, far from land. A preconditioning situation
(gyre) and circulation causes the surface to deform and intense surface forcing occurs due to background
cyclonic circulation. After water evaporates, salt remains and creates denser water which sinks and
spreads into the deep water.
The other type of convection in the ocean is near boundary convection. Near boundary convection occurs
near as solid boundary, such as land. With the boundary, a dense water reservoir is made in the ocean.
Remaining water will be more salty and denser. This dense water sinks due to water evaporation and
remaining salt. The dense water moves horizontally to the deep-water zone.
There are three phases of deep water convection, precondition which is on the large scale occurring at a
scale of 100km, deep convection plumes which occurs localized at a scale of 1km, and lateral exchange
which is between the connection site and the fluid through advection processes at a scale of 30km.
5.3) Why is there a depth of minimum sound speed? Why is the layer around that depth called
sound channel?
Acoustic waves are dependent on temperature and pressure, because of this there is a depth of minimum
sound speed which follows acoustic properties. The speed that sound travels depends on temperature and
pressure. Sound speed at the surface of the ocean is faster because the water temperature is warmer from
the sun heating the upper layers. As the water depth increases the water temperature gets colder until it
reaches a constant value of 2
o
C at about 1000m in the mid-latitudes. So sound speed is decreasing linearly
with increasing depth due to the decreasing temperature. Pressure also effects sound speed. Pressure
increases with depth and sound speed increase linearly with pressure. As you increase pressure you
increase your sound speed. As shown in the chart, the minimum sound speed in the mid-latitudes is about
1000m. Where sound speed is decreasing with temperature until then, and after increases with depth.
Salinity does not have a great effect on sound speed compared to temperature and pressure.
The layer around this depth of minimum sound speed is called a sound channel because it forms a channel
which sound can propagate over long distances.
5.4) How do ARGO floats work? What do they measure?
An ARGO float is a type of ocean drifter or floater used for taking measurements of temperature, salinity
and currents in the ocean. ARGO floats work by floating on the water surface for about 6-12 hours to
transmit data to a satellite. Then the ARGO sinks to a predetermined depth with a speed of 10cm/s by
reduce its volume and increasing its density with a hydraulic bladder. When ARGO reaches its desired
depth, it moves horizontally for approximately 9 or 10 days recording and measuring data. When the time
is up the ARGO returns to the surface by increasing its volume with the hydraulic bladder and sends the
data back to the satellite and sends a signal to be retrieved. ARGO floats not only measure ocean currents
at different water depths they also measure temperature and salinity while they are traveling and while
they are ascending/descending.
5.5) What variables of interest to physical oceanography can be derived using visible range,
infrared, and microwave sensors, respectively? What inherent problem is there with passive
microwave retrievals?
Using visible range, infrared, and microwave sensors are very important to physical oceanography and
are all part of the electromagnetic spectrum. Visible range can be used to see visible colors on the ocean
that can be related to biological productivity and the amount of chlorophyll on the ocean surface. Infrared
sensors use heat to see sea surface temperature patterns. Microwave sensors use reflection/radiators to see
the microwave emission of ice and can be used to derive sea ice concentrations. Microwave sensors can
also be used for sea-surface salinity,
surface wind speed, and dynamic topography including wind
generated waves, gyres, eddies and currents.
With passive microwave retrievals the microwave signals need to be converted to the sea ice
concentrations using many different algorithms, these different algorithms yield different results which
can cause problems.
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