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
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
- 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
- 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?
5 September, 2004