Combined Homework and Laboratory Set 5
Due 8 March 2004
Late homework will cost 15 points per week or part of a week it is late.
Stability in the Ocean Using Java Ocean Atlas
The goal of this laboratory session is to learn more
about stability using data from a meridional section across
the South Pacific and functions available in
OceanAtlas for Macintosh was developed by John
Osborne at the NOAA Pacific Marine Environmental Laboratory,
James Swift at the Scripps Institution of Oceanography, and
Edward Flinchem of Seattle.
- Do the work using the copy of OceanAtlas you used for
the last assignment.
- The software allows you to look at the internal
structure of the oceans, including temperature, salinity,
density, potential density, and stability frequency, as a
function of depth and as cross-sections using
hydrographic data collected by various expeditions to the
Atlantic, Pacific, and Indian Ocean.
For this laboratory:
- If you did not download data files with Java
OceanAtlas, download and unstuff the
JOA_data_preWOCE.sit.hqx from JOA
Data Files at the OceanAtlas
ftp site. It contains data from all the oceans.
- Open Java
OceanAtlas, then open S.Pacific
150_W.poa data file. It is in the JOA_data_preWOCE, Pacific
- Under Plots, choose Map, choose the
southern hemisphere, then Print the map. If you like, you
can select a part of the map and JOA will plot the
- Under Calculations, choose
Parameters... Check N under
Frequency (Hz) and Sigma-0. Click OK. This will
calculate the buoyancy frequency and store it in the
- Under Plots, choose Contour,
then choose BV3 on PRES; 0-6000.srf: Y-axis range 0-1000
with increments of 100, Style: Color fill w/contours;
Offset: Distance; Markers: Observations. Create autoscale
color bar by clicking on the linear plot. Click
Plot. The program should now open a new window
with the contour plot of stability frequency as a
function of depth.
- Print the contour plot.
- Data points in the contour plot window are linked to
data points and locations in the data window S. Pacific
150° W. Moving among the data points at the bottom of the
data window also moved the pointer in the contour plot.
Use this feature to find values for variables in the data
window corresponding to features in the contour
- In answering the questions below, you may also want
to make other contour plots.
- Which side of the plot is to the north, which to the
south? Label the print of the plot.
- What is Sigma-0?
- Where is the maximum buoyancy frequency? Latitude,
- Why is there a maximum at this location? That is,
what physical processes in the upper ocean lead to the
formation of a maximum in this location?
- Where is the minimum?
- Note these locations on the plot.
- Comment on the feature at a depth near 60 decibar
depth at station 230. What might cause such a
prominent, isolated minimum?
- JOA uses pressure in decibars instead of depth in
- How is pressure related to depth?
- What is the approximate depth of the maximum
- What is the depth of the 1000 dbar level at
station 231 using approximate density from that
station (pick an approximate density typical of the
upper 1000 decibars of the water column).
- Does the salinity or temperature gradient seem to be
more important in determining buoyancy frequency along
150° W? Please give reasons for your answer, referring
to the data or plots in support of your statements.
- Is there a mixed layer?
- Please give reasons for your answer, referring to the data or
plots in support of your statements.
- Where is the maximum of the buoyancy frequency relative to the
mixed layer? In answering this question review the definition of
a mixed layer.
- Describe two processes that might cause temperature of the mixed
layer at mid latitudes to become cooler at the end of summer.
- Why is there no mixed layer in some regions?
- What other processes seem to influence the buoyancy
frequency along 150° W? Please give reasons for your
answer, referring to the data or plots in support of your
- Are there any regions in the plot where
double-diffusion instability might be important?
- If there are regions, where are they?
- Which type of instability exists?
- What will the instability do to the density profile?
- Why is salinity at the surface higher at lower
latitudes for this section?
5 September, 2004