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Physical Oceanography
Combined Homework and Laboratory Set 7
Due 8 April 2004

Late homework will cost 15 points per week or part of a week it is late.


In this homework set you will learn more about the use of sea-surface temperature and sea-surface height measured from space to help determine ocean-surface geostrophic currents. You will compare various current maps and calculations produced by Bob Leben's group at the University of Colorado and the US Navy. The Navy maps are a major component of the Global Ocean Data Assimilation Experiment GODAE.


Surface Geostrophic Currents from Altimetry

The goal of this work is to learn more about using altimeter data to study surface geostrophic currents in the ocean. Satellite altimeter data are available from many sources. Today lets look at maps of the topography of the Gulf of Mexico produced by the Colorado Center for Astrodynamics Research (CCAR) at the University of Colorado. In particular, look at the Real-Time Altimeter Project page,

The group at the Colorado Center is calculating the topography of the Gulf of Mexico using Jason, Topex/Poseidon, Geosat Follow-On(GFO) and ERS-2 altimeter data processed in near real-time, usually within 12 to 36 hours of overflight.

Download and print the Latest Sea Surface Height Map for the Gulf by clicking on the submit values, using the default values. Also download and print the latest map with sea-surface temperature overlay. Then answer the following questions.

  • What is the date of the map, and what is shown on the map?
  • What is the relationship between the information displayed on the map and surface currents? In answering the question, please be specific.
    • Are there quantitative relationships between values on the map and currents?
    • What are the relationships? etc.
  • Using the map, describe the currents in the Gulf on the date shown on the map.
    • Where do currents enter and leave the Gulf?
    • Are there any eddies in the Gulf?
  • What is the approximate velocity of the current entering and leaving the Gulf?
  • If there are eddies, what is the approximate velocity of the current in the eddy? Using this value, what is the approximate rotation rate of the eddy in cycles per month?
  • Compare the map for November 29, 2003 with sea-surface temperature overlay with the same map you produced above.
    • How do they differ?
    • Is temperature closely related to sea-surface height?
    • If not, why not?
  • Look at sea-surface temperature maps for the Gulf of Mexico for September produced by the Ocean Remote Sensing group at the Johns Hopkins University Applied PhysicsLlaboratory.
    • Download a 7-day composite September map of sea surface temperature for the Gulf of Mexico. It can be for any year, 2003, 2002 or...
    • Does the map show any correlation with expected current?
    • Why not?

Now let's look at a similar product produced by the U.S. Navy's Real-Time Ocean Environment page.

  • Click on the image of the Gulf of Mexico and from the Gulf of Mexico page download and print the recent MODAS SST and NLOM SSH maps. Compare them with the similar maps from the Colorado Center for Astrodynamics Research.
    • Are they based on the same data?
    • Are the maps essentially the same, or different?
    • If different, how do they differ?
  • Click on section 1 on the Gulf of Mexico page for temperature to bring up a cross-section of temperature vs depth along the section. Print the section.
    • On the printed section show the location of strong currents.
    • How deep do the currents extend?

Now let's look at the forecasts of ocean currents by the U.S. Navy using their Navy layered Ocean Model NLOM.

  • Download and print the latest map of Sea-Surface Height/Currents Nowcast for the Inter-Americas Seas at the top of the page.
  • Download and print the forecasts for the same day from the SSH Forecast archive for 1-day, 8-day, 15-day, 22-day and 29-day forecasts. For example, if the nowcast is for 25 March 2004, use the forecasts for that day initialized on 24 March 2004, 17 March 2004, 10 March 2004, 3 March 2004, and 25 February 2004.
    • How far into the future can currents in this region be forecast with useful accuracy?
    • What do you mean by useful accuracy? To answer this question, you may need to pick some oceanographic problem that requires a forecast, such as ship routing, or planning of oil-drilling operations.
    • Look at but don't print out, the same forecasts for sea-surface temperature. How far into the future can sea-surface temperature be accurately forecast?
    • Why might the sea-surface temperature forecasts be less useful than sea-surface height forecasts?

Updated on: 5 September, 2004

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