: Generate the Southern Oscillation Index by standardizing
the differences in sea-level pressure anomalies at Tahiti and Darwin.
|Locate Dataset and Variable
Select the "Datasets by Catagory" link in the blue banner on the Data Library page.
- Click on the "Climate Indicies" link.
- Select the
Indicies Tahiti dataset.
- Click on the "sea level pressure" link under the Datasets and Variables subheading.
- Click on the "sea level pressure" link again under the Datasets and Variables subheading.
Notice that sea level pressure anomaly and standardized sea level pressure are also variables contained in this dataset.
These are variables that will be computed in this example, however you may select them in the future to save time.
|Select Temporal Domain
- Click on the "Data Selection" link in the function bar.
- Enter the text Jan 1960 to Apr 2004 in the Time text box.
- Press the Restrict Ranges button and then the Stop Selecting button.
- Click on the "Filters" link in the function bar.
- Choose the anomalies command. CHECK EXPERT
This operation calculates the difference between monthly climatology and the original data. These anomalies are not standardized.
|Standardize (Normalize) Tahiti Anomalies
- Click on the "Expert Mode" link in the function bar.
- Type the following command under the text already there:
- Press the OK button. CHECK
The standardize function divides each anomaly by the standard deviation of the data.
The result is a time series of standardized sea level pressure anomalies at Tahiti.
|Enter Darwin, Australia Standardized Anomaly Data
Southern Oscillation Index from January 1960 to April 2004
- To see the results of this operation, choose the time series viewer.
The resulting image is a graph of the SOI over the previous 44 years. Negative values
represent higher-than-average surface pressures at Darwin and lower-than-average
surface pressures at Tahiti, which in turn, often correspond to El Niño conditions.
The exceptionally strong El Niño event of 1982 / 1983 is prominent in this figure.