20CR Climate Indices: Southern Annular Mode (SAM)
- Description:
- 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.
- Image:
- 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):
- sam.20crv2c.mon.ncl
- Time Interval: Monthly
- Time Coverage: 1851 to 2011 (V2c)
- Update Status: none
- Get Data:
- Update Status: none
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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?)
- Source:
- Data is calculated at PSL using method in paper below.
- References:
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- Geophysical Research Letters, Vol. 26, No.4 pages 459-462 DOI: 10.1029/1999GL900003 "Definition of Antarctic Oscillation index" Daoyi Gong, Shaowu Wang
- See annular modes webpage at Colorado State
- Other Links
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- AAO from the 20th Century Reanalysis.
- AAO/SAM from JISAO
- NOAA/NCEP Climate Prediction Center (CPC) AAO monitoring page
Spatial pattern of the SAM for January-December (correlation with SLP from NCEP/NCAR Reanalysis). |