The ESRL website will be unavailable for 24 hours starting Friday, March 6th at 5:00pm MT due to building maintenance.

20CR Climate Indices:SOI

This mode describes variability of the tropical atmosphere. It is often used as a measure of El Nino/La Nina and is correlated highly with ENSO indices. A high value represents higher surface pressure in the eastern tropical Pacific with more typical easterlies along the equator and is associated with La Nina's. A low value is associated with tropical surface westerlies and El Ninos.
Correlation of the 20CR-derived SOI timeseries and SLP from the NCEP/NCAR Reanalysis for 1948 to 2011.
Calculation Method:
We used the definition in Ropelewski 1987 MWR. Surface pressure at the grid points nearest to Tahiti and Darwin represent the timeseries at those two locations. Each timeseries is first standardized using the 1981-2011 monthly climatology. The Tahiti minus Darwin timeseries is calculated. This timeseries is then re-normalized using the entire time period for the standardization.
Time Interval: Monthly
Time Coverage: 1871 to 2011
Update Status: none

Get Data:
SOI index: Standard PSD Format (What is standard format?)
SOI index: Standard PSD Format (1948 onwards version)(What is standard format?)
NOAA/ESRL PSD using method in reference below.
  1. Ropelewski, C.F. and Jones, P.D., 1987: An extension of the Tahiti-Darwin Southern Oscillation Index. Monthly Weather Review, 115, 2161-2165.
  2. NOAA/NCEP Climate Prediction Center (CPC) SOI monitoring data
Other Links
  1. See History of the SOI