20CR Climate Indices: Southern Annular Mode (SAM)

This mode describes low frequency variability of the Southern Hemisphere extratropics. A positive index (lower polar pressure) is associated with weaker, zonal winds in the extratropics. A negative value is associated with stronger zonal winds.
Spatial pattern of the SAM for January-December (correlation with SLP from NCEP/NCAR Reanalysis).
Calculation Method:
This version of the SAM is calculated using SLP from the 20CRV2c. (SAM) is defined as the difference of zonal mean sea level pressure between 40°S and 65°S. The zonal means at 40°S and 65°S are each calculated. Each month's zonal mean is standardized by the mean/standard deviation determined for the climatological time period (1981-2010). Then, the 65°S value is subtracted from the 40°S value for each month.
Download generation code (NCL):
Time Interval: Monthly
Time Coverage: 1851 to 2011 (V2c)
Update Status: none

Get Data:
SAM index: Standard PSL Format(20CRV3: 1836-2014) (What is standard format?)
SAM index: Standard PSL Format(20CRV2c) (What is standard format?)
SAM index: Standard PSL Format(20CRV2c) (1948 onwards version)(What is standard format?)

Data is calculated at PSL using method in paper below.
  1. Geophysical Research Letters, Vol. 26, No.4 pages 459-462 DOI: 10.1029/1999GL900003 "Definition of Antarctic Oscillation index" Daoyi Gong, Shaowu Wang
  2. See annular modes webpage at Colorado State
Other Links
  1. AAO from the 20th Century Reanalysis.
  2. AAO/SAM from JISAO
  3. NOAA/NCEP Climate Prediction Center (CPC) AAO monitoring page