EARTH SYSTEM SCIENCE
WRITING ASSIGNMENT # 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 answers for the written questions 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 our basic tools (Windows Movie Maker) to download a number of images so that we can create "time-lapsed" images 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, scroll down and click on the "Monthly Time Series Images" link.
3. Once on the "Science " page, click on one of the bars for "Monthly Global SSH and SST" of the calendar.
4. Select a month and a year, then dowload the corresponding images of both SSH and SST to your computer. (By the way, you should detemine what SSSh and SST mean at this point).
5. Select imagery for 1997 and 1998, two consecutive years that are available.
8. Load these images into Windows Movie Maker. When the images are loaded, 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 continued into 1998, so if you can add some 1998 images if you want to see how the movie ends. Make a similar movie showing variation in sea surface temperature anomalies for the same time interval.
QUESTIONS TO ANSWER:
1. What is the magnitude of the sea surface anomaly in the eastern tropical Pacific? (i.e. how tall is it?)
2. 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?
3. 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 2002 (48 images). Once these images are downloaded, paste them into Windows Movie Maker 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 ANSWER:
1. Does anyone know what is meant by calling these drifters "Lagrangian"?
2. Print a hard copy of one of your images and identify the areas where the Gulf Stream and other currents in the North Atlantic (e.g. the Labrador Current, North Atlantic Drift, Canary Current, the Antilles Current, etc.) should be. Once you have labelled your map, compare it to the motion observed on your animation. Can you verify the presence of each of these currents?
3. Do the drifters move to the center of gyre? What causes this?
4. 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
