SO231 General Oceanography Fall 2000

Temperature, Salinity, and Density in the Pacific Ocean

 

If you need help with the computer programs, note that there is help available and that it has an index which you can Search.

 

You should understand the following after this lab:

a.  Variation in surface water temperature with latitude.

b.  East-west variation in surface water temperature in the major ocean basins.

c.  The variation in salinity and temperature in the deep isothermal layer throughout the Pacific.

d.  Latitudinal trends in the thickness of the mixed surface layer and thermocline, and in the depth to the sound channel.

e.  Latitudinal variation in the water column on a T-S diagram.

This lab is a precursor to two that will deal with geostrophic currents, probably the hardest concept in this course.  Insure that you understand what we are doing in this lab or you will be in trouble later.

 

MCSST Map

 

Use the SST-CZCS program to look at a map of MCSST (multi-channel sea surface temperature) for the month on August.  This map comes from the AVHRR instrument on NOAA's polar orbiting satellites.  You load a file with the File, Load option.  The file names are SNYYDDDI.BMP, where “SN” stands for  sea surface temperature, Night, YY is the year, and DDD is the Julian day, and “I” means they interpolated for missing data.  Pick one of the August dates, and you should probably avoid the 1982-83 “mother all El Ninos” to date (excluding perhaps the one just ending).  You can use the mouse function to move around and see the surface temperature at any location you want.  The Modify, Blowup will make the image large, and you can Overlay a latitude grid.  Double clicking will post the temperature value on the screen.

 

Before answering the question, look at the Movie, Play option.  Think about what the overall pattern shows: high temperatures are in purple and red, cold water in blue.

 

1.  What is the surface temperature at each of the following latitudes in the Pacific during August (perhaps a single value will not be sufficient, and you need to show the trend across the ocean basin):

Equator:   

 

Tropics (23½° N and S):

      

 

Mid latitudes (45° N and S):

       

 

Polar circles (66½° N and S):

      

 

 

2.  Are your answers different for the two hemispheres?  Why or why not?

 

 

3.  Which side of the north Pacific Ocean appears to have warmer water, the coast of North America or the coast of Asia?

 

 

 

4.  Which side of the south Pacific Ocean appears to have warmer water, the coast of South America or the coast of Australia?

 

 

 

5.  Do the same trends appear to hold in the Atlantic Ocean?

 

 

 

6.  Can you generalize about which side of an ocean basin is heated by the transfer of warm water from the equator, and which side is cooled by the transfer of cool water from the poles?

 

 

 

 

 

 

T-S Profiles and Plots

 

Select the TSPLOT program, and then the pacific.rom data set.  The pacific.rom data set consists of CTD data taken by various oceanographic ships.  This consists mostly of data taken during the month of August, supplemented in some cases by data from other months for those parts of the Pacific not visited by research vessels during August.

 

1.   Where are the highest surface salinities in the Pacific?  Why is this the case?  (Use View, Map Surface, Salinity)

 

 

 

2.  Where are the lowest surface salinities in the Pacific?  Why?

 

 

3.  Look at overlaid single station depth profiles of temperature, salinity, and sound velocity  at each of the following latitudes.  (Use View, Depth Profiles, and note that after picking your stations and displaying them for one parameter, you can switch to another parameter easily on the same graph (by using the Parameter menu choice) or you can open multiple graphs).  How does each parameter vary through the Pacific, and between summer and winter?

Equator:

 

Tropics (23½° N and S):

 

Mid latitudes (45° N and S):

 

Polar circles (66½° N and S):

 

 

 

 

 

4.  Look at T-S diagrams for the same locations. (Also uses View, Depth profiles, or you can just change the Parameter on another graph). Compare the surface waters and the water at depth.

 

 

 

5.  Construct a N-S profile through the Pacific, and look at temperature and sound velocity. (View, Profile Contours.) How does the thickness of the mixed surface layer and the thermocline vary with latitude?  How does the depth of the sound channel vary?   You may want to rescale the depth to concentrate on that part of the profile that has significant changes, and adjust the contour interval for the Sound Velocity diagram..

 

 

 

 

6. Which parts of the Pacific have no August data?   Why?  To plot the data by month, go to Other, Highlight, Station, Month.  (These areas benefit the most from the availability of satellite data.)