# Part 3—Discover SST Associated with El Niño and La Niña

## Step 1 – Investigate an El Niño Year

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?
1. We have already calculated the average SST for the period of 1982 to 1998 (Overall Average). Now calculate the average SST for Dec. 1997. Enter Monthly Average, Dec 1997 as the name for the result.
2. To view the differences between two grids is 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."
3. 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.

## Step 2 – Investigate a La Niña Year

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.

1. Create a monthly average from the five weeks of 1998. Enter Monthly Average, Dec 1998 as the name for the result.
2. Subtract the overall average from the 1998 average.
3. 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.

## Step 3 – Choose Another Year to Analyze

1. Choose another year to do a similar analysis. Decide if that year was an El Niño , a La Niña year or a "normal" year.
2. Hint: 1982 was considered another strong El Niño year while the next year, 1983, was considered to be a La Niña year.
3. Compare the following difference images for each year with your selected year.
4. Compare your interpretation with a SST anomaly graph for the Pacific Ocean located along the equator. How does your year fit into the overall trend of SST? Try comparing this graph with another year.
5. Hint: Try showing one year at a time from above while comparing it to the SST Anomaly graph below.