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.
- 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.
Temporal Coverage
- Monthly values: 1851/01 to 2011 (V2c)
- Monthly values: 1871 to 2012 (V2)
- Update Status:Static: Static
Data Notes
- Units: mb
- Missing data value: -99.0
Time-series List
-
SAM index: Standard PSL Format(20CRV2c) (What is standard format?)
SAM index: Standard PSL Format(20CRV2c) (1948 onwards version)(What is standard format?)
SAM index: Standard PSL Format(20CRV2) (What is standard format?)
SAM index: Standard PSL Format(20CRV2) (1948 onwards version)(What is standard format?)
Usage Restrictions
- None
Caveats
- None
Related Time-series
Links
- AAO from the 20th Century Reanalysis.
- AAO/SAM from JISAO
- NOAA/NCEP Climate Prediction Center (CPC) AAO monitoring page
Analysis pages
Original Source
- Data was calculated at NOAA/PSL. Download generation code (NCL):sam.20crv2c.mon.ncl
Time-series source dataset(s)
- Input data for the mode calculation is the 20CR Datasets.
References
- 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
- 20CR citations