MARINE GEOLOGY - GEOL 5533
LABORATORY #6 - MAPPING OCEAN CURRENTS
This week's assignment will involve downloading image sets from two important programs involved in observing ocean dynamics. The TOPEX/Poseidon mission and the deployment/analysis of drifting buoys around the world. These sites provide a great resource for observing and understanding the basics of ocean dynamics as presented in our class. Follow the instructions below to complete the animations for this week and answer the questions that follow. Submit your animations and your answers via e-mail before next Monday. Most of all, have fun with the assignment - these are very cool data sets!
YOUR ASSIGNMENT FOR THIS WEEK:
Your assignment this week will be to observe the pattern of ocean circulation. There are a number of interesting ways to tackle this truly global problem. Recently, satellites (such as TOPEX) have been launched to take "snapshots" of Earth. A longer term but equally impressive activity is the launching of drifting buoys. We will use a new tool (Windows Movie Maker) to download a number of images so that we can create "time-lapsed" animations illustrating ocean dynamics.
Here's what to do:
EXERCISE 1:
1. Go to the TOPEX/Poseidon archive by clicking on the link at the bottom of the page.
2. From the TOPEX/Poseidon Home Page, click on the "Science and Data" link.
3. Once on the "Science and Data" page, look under "Data Sources" for TOPEX/POSEIDON Altimeter products for Research and Applications.
4. Scroll through the page to see the types of data that are available for educational and research uses. At the bottom of the page, there is a link for "TOPEX/POSEIDON "Quick-Look" & 10-Day Browse Images and Data (NASA/PO.DAAC)". Follow the underlined link.
5. Once at the TOPEX/Poseidon archive page, locate 10-Day Browse Images and go to the archive page.
6. Click on the data for "1997" (new format). The table that appears is a list of all available imagery for 1997 on 10-day cycles (i.e. one image ca. each two weeks).
7. The abbreviations SWH, SSA, WSP, WVC stand for Significant Wave Height, Sea Surface Anomaly (Dynamic Height), Wind Speed, and Water Vapor Content. We want to look at SSA. Begin dowloading these images in the same way we have done before (i.e., click on a 10-day cycle to view the image. Once the image loads, click on the right mouse button and select "Save Image As" and direct the image to your disk Alternatively, you can "Copy" the image and "Paste" it into WWW Gif Animator. Download all images for 1997.
8. Load these images into WWW Gif Animator. Resize all images to 480 x 320 pixels. When the images are loaded, optimize the animation (from the menu bar, choose "Edit" then "Optimize"). You can now observe how the dynamic topography of the ocean changed during 1997. Some of this change is seasonal, but a significant anomaly developed in the eastern tropical Pacific Ocean related to El Nino. Note the time-interval over which this anomaly developed. It continues into 1998, so if you can add some 1998 images if you want to see how the movie ends.
QUESTIONS TO CONSIDER:
What is the magnitude of the sea surface anomaly in the eastern tropical Pacific? (i.e. how tall is it?)
How does the TOPEX satellite measure the elevation of the sea surface? What factors need to be taken into account to be able to generate sea surface elevations?
Try to estimate the actual geographic size of the sea surface anomaly in the eastern Pacific Ocean. Compare the size of this anomaly to nearby continents (North and South America). How big is it? Try to estimate the average height of this anomaly, then estimate the volume of water contained within it.
EXERCISE 2:
1. Go to the Global Drifter Center by clicking on the link below.
2. Find the "DAC Data Products" link and follow it.
3. Scroll down the "DAC" page to the "Monthly Drifter Maps". Here, we will find many images from different ocean basins which show the progress of drifters on a monthly basis. These images come is a variety of sizes and have been produced and modified since the time they began placing them online, so there are some complications to pasting them together to make animations. But we will try to ignore those and proceed anyway.
4. Select data for the "North Atlantic". Display then download images beginning Jan 1999 and ending Dec 2000 (24 images). Once these images are downloaded, paste them into WWW Gif Animator to observe the circulation of the North Atlantic. Watch the movement of the drifters over time.
If you wish, you can repeat this process with data from other ocean basins (the North Pacific and Indian Oceans work well.
QUESTIONS TO CONSIDER:
Does anyone know what is meant by calling these drifters "Lagrangian"?
Can you identify the Gulf Stream and other currents in the North Atlantic (e.g. the Labrador Current, the Antilles Current, etc.)?
Do the drifters move to the center of gyre? What causes this?
Observe the motion of the red arrows versus the motion of the blue arrows. What do these two colors represent? Why do their motions differ?
TOPEX/POSEIDON HOME PAGE THE GLOBAL DRIFTER CENTER
