Part 2 Discover SST Associated with El Niño and La Niña

Part 2—Discover SST Associated with El Niño and La Niña

Step 1 – Investigate an El Niño Year

1. 1997 was considered a strong El Niño year. Let's see if the data supports that claim. What pattern of SST would you expect to observe in the Pacific if it were a strong El Niño year?

2. We have already calculated the average SST for the period of 1982 to 1998 (Overall Average). Now calculate the average SST for Dec. 1997. (Use previous instructions if you’ve forgotten how). Enter Monthly Average, Dec 1997 as the name for the result.

3. To view the differences between two grids you will need to generate a "difference" image. A difference image will show the "departure from normal" of each location as red if it is warmer than normal and blue if it is cooler than normal. This is known as an anomaly, or difference, map. Subtract the overall average from the 1998 average and name the result "1997 Difference from Overall Average."

a) Click the Analyze tab and Add a new field to the table of the Weekly Means of SST layer by Computing a difference between the 1997 average and the Overall Average.

b) Enter a Result name of "1997 Difference from Overall Average"

c) Your screen should look like this:

4. Apply a standard color scheme to your difference image that you'll be able to copy to other ones. Choose the red-white-blue color scheme and change the minimum temperature to -2 and the maximum temperature to 2.

a) Double-click the "Weekly Means of SST layer." to open the edit appearance window.

b) Colorscheme: red-white-blue

c) Check reverse box. (Very important)

d) Min: -2 Max: 2

e) Apply and close

5. Does this difference image agree with your prediction? Is this pattern consistent with a strong El Niño year?

Step 2 – Investigate a La Niña Year

1. The following year after this strong El Niño event, a La Niña set up in the Pacific Ocean. As you did for the El Niño year, predict what pattern in SST would you expect to observe in the Pacific if it were a strong La Niña year

You have already calculated the average SST for the period of 1982 to 1998. Next you will need to calculate the average SST for Dec 1998 and then subtract the Overall Average from it. This calculation will show you the difference between "normal" and the 1998 year. To do this:

2. Create a monthly average from the five weeks of 1998. Enter Monthly Average, Dec 1998 as the name for the result.

a) Click the Analyze tab.

b) Under Add field(s) to Layer, choose By Math Operation.

c) In the "Add Field to the Table of" dialog box, use the drop-down menus to Add a Field to Weekly Means of SST by Computing a difference.

d) Hint: Use the Deselect All before making your selection of the 1998 fields. This way you won't include any other years in the analysis.

e) Enter Monthly Average, Dec 1998 as the name for the result.

3. Subtract the overall average from the 1998 average.

a) Click the Analyze tab and Add a new field to the table of the Weekly Means of SST layer by Computing a difference between the 1998 average and the Overall Average.

b) Enter a Result name of "1998 Difference from Overall Average".

a. Double-click the "Weekly Means of SST layer." to open the edit appearance window. Choose the following settings:

· Colorscheme: red-white-blue

· Check reverse box. (Very important)

· Min: -2 Max: 2

b. Apply and close

5. Does this difference image agree with your prediction? Is this pattern consistent with a strong La Niña year?

Step 3 – Choose Another Year to Analyze

1. SEE ME and I will assign you another year to do a similar analysis. Decide if that year was an El Niño, a La Niña year or a "normal" year. You can do this with the following steps:

a) Create a monthly average for the weeks of the selected year

b) Subtract the overall average from the selected year average

c) Apply the standard color scheme to your difference image

d) Interpret the difference image. Is it an El Niño, a La Niña or a "normal" year.

2. Once you have created the difference image, take a screen shot of this image and cut/paste it into a Word document. MAKE SURE EACH PERSON HAS A COPY OF THIS IMAGE. ON YOUR OWN, create a well-written CLAIM, EVIDENCE, AND REASONING for you believe this year was an El Niño, a La Niña year or a "normal" year. THIS IS AN INDIVIDUAL ASSESSMENT. YOU MAY WORK WITH YOUR PARTNER, BUT IT SHOULD BE IN YOUR OWN WORDS. Your explanation should include:

3. Turn your explanation in to me along with any notes you took along the way. You will receive an individual grade for this. If you choose to turn one paper in for both partners, I will automatically split your grade in ½! Yikes!