A station based Southern Annular Mode index from 1884-2005
The Southern Annular Mode (SAM) is a large scale mode of atmospheric variability and arguably the most significant forcing of intraseasonal to decadal climate variability in the middle to high latitude Southern Hemisphere. Statistical analysis revealed a largely zonally-symmetric mass sea-saw between the subtropical latitudes centered at 45ºS and the Antarctic continent which is characteristic of the strength and position of the circumpolar westerlies (Hall and Visbeck, 2002; Visbeck and Hall, 2004).
A thematic website for annular modes can be found at http://ao.atmos.colostate.edu/
Atmospheric pressure observations from the Southern Hemisphere are used to estimate a monthly index of the Southern Annular Mode back to 1884. The analysis groups all relevant observations in four regions, one for Antarctica and three in the subtopical belt. By the end of the 19th century pressure observations are available at a number of locations in the subtropical regions. Systematic observations in the subpolar regime around the Antarctic continent began only during the 1940-1960 period seriously compromising the length of a traditional SAM index. Here estimates of Antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 20ºS. A detailed description of the methods used is given in a paper submitted to the Journal of Climate.
(pdf)
Publikations
Hall, A. and M. Visbeck, 2002: Synchronous Variability in the Southern Hemisphere Atmosphere, Sea Ice, and Ocean Resulting from the Annular Mode. J. Climate, 15, 3043-3057.
Visbeck, M., and A. Hall, 2004: RESPONSE To - Comments on "Synchronous Variability in the Southern Hemisphere Atmosphere, Sea Ice, and Ocean Resulting from the Annular Mode." J. Clim., 17(11), 2255-2258.
Visbeck, M., 2009: A station-based Southern Annular Mode index from 1884 to 2005. J. Climate, 22, 940-950. (pdf)
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 Figure 1. Upper panel: The top four time series represent annual averaged sea level pressure (SLP) indices for the regions of South Africa, South America, Australia/New Zealand, and Antarctica (see also Table 1 for the names of individual stations). Note, that the pressure anomalies for Antarctica have been reversed to better show the anticorrelation. The lower time series is the reconstructed index for Antarctica based on the upper three time series (see text for details). Lower panel: The final annual averaged SLP index is shown together with the number of individual stations that have been used. The dashed line indicates the year 1954. Before 1954 the proxy SLP index for Antarctica was used to derive the SAM index. |
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 Figure 2. Black stars represent locations of SLP stations used for SAM index calculation. Open circles represent other stations not used here. Gray shading represents the correlation between the monthly SAM index and the NCAR/NCEP reanalysis 850 hPa geopotential anomaly between 1970 and 2002. Negative correlation is indicated by dotted contour lines. |
|
Station Name |
lat |
lon |
Start of record |
SAM correl. |
Regional correl. |
|
Antarctica |
|
|
|
|
|
|
ESPERENZA + HOPE BAY |
-63.4 |
303.0 |
1945 |
-0.73 |
0.86 |
|
ORCADAS |
-60.8 |
315.3 |
1903 |
-0.40 |
0.73 |
|
HALLEY BAY |
-75.5 |
333.4 |
1956 |
-0.82 |
0.82 |
|
SIGNY ISLAND |
-60.7 |
314.4 |
1947 |
-0.62 |
0.75 |
|
BELLINGHAUSEN |
-62.2 |
301.1 |
1944 |
-0.66 |
0.82 |
|
MARAMBIO |
-64.2 |
303.3 |
1971 |
-0.72 |
0.83 |
|
FREI |
-62.2 |
301.0 |
1969 |
-0.60 |
0.77 |
|
B.A.ARTURO PRAT |
-62.5 |
300.3 |
1966 |
-0.62 |
0.78 |
|
BERNADO O'HIGGINS |
-63.3 |
302.1 |
1963 |
-0.65 |
0.78 |
|
ROTHERA 68DEG S |
-67.6 |
291.9 |
1946 |
-0.69 |
0.82 |
|
FARADAY&PORT LOCKROY |
-65.2 |
295.7 |
1944 |
-0.67 |
0.82 |
|
NOVOLAZAREV |
-70.8 |
11.8 |
1961 |
-0.77 |
0.72 |
|
SYOWA |
-69.0 |
39.6 |
1957 |
-0.79 |
0.78 |
|
MOLODZNAJA |
-67.7 |
45.9 |
1963 |
-0.81 |
0.81 |
|
MAWSON |
-67.6 |
62.9 |
1954 |
-0.75 |
0.75 |
|
DAVIS |
-68.6 |
78.0 |
1957 |
-0.78 |
0.77 |
|
MIRNY |
-66.5 |
93.0 |
1956 |
-0.72 |
0.71 |
|
CASEY |
-66.3 |
110.5 |
1957 |
-0.74 |
0.73 |
|
DUMONT DURVILLE |
-66.7 |
140.0 |
1956 |
-0.69 |
0.66 |
|
SCOTT |
-77.8 |
166.8 |
1957 |
-0.73 |
0.67 |
|
South Africa |
|
|
|
|
|
|
DURBAN |
-30.0 |
30.9 |
1884 |
0.50 |
0.89 |
|
PORT ELIZABETH |
-34.0 |
25.6 |
1887 |
0.53 |
0.92 |
|
CAPE TOWN |
-34.0 |
18.6 |
1841 |
0.44 |
0.76 |
|
MAPUTO |
-25.9 |
32.6 |
1910 |
0.44 |
0.86 |
|
GOUGH ISLAND |
-40.4 |
-9.9 |
1942 |
0.33 |
0.39 |
|
MARION ISLAND |
-46.9 |
37.9 |
1948 |
0.33 |
0.45 |
|
Australia and New Zealand |
|
|
|
|
|
|
CHRISTCHURCH |
-43.5 |
172.6 |
1864 |
0.40 |
0.90 |
|
ADELAIDE |
-34.9 |
138.5 |
1857 |
0.24 |
0.55 |
|
AUCKLAND |
-37.0 |
174.8 |
1863 |
0.37 |
0.83 |
|
DUNEDIN AIRPORT |
-45.9 |
170.2 |
1864 |
0.39 |
0.88 |
|
WELLINGTON |
-41.3 |
174.8 |
1864 |
0.41 |
0.92 |
|
SYDNEY |
-34.0 |
151.2 |
1859 |
0.30 |
0.68 |
|
HOBART AIRPORT |
-42.8 |
147.5 |
1866 |
0.30 |
0.75 |
|
HOKITIKA |
-42.7 |
171.0 |
1866 |
0.42 |
0.93 |
|
CHATHAM ISLAND |
-44.0 |
183.4 |
1930 |
0.38 |
0.82 |
|
CAMPBELL ISLAND |
-52.5 |
169.2 |
1941 |
0.21 |
0.62 |
|
South America |
|
|
|
|
|
|
ASUNCION |
-25.3 |
302.4 |
1893 |
0.41 |
0.78 |
|
CORDOBA ARGENTI |
-31.4 |
295.8 |
1873 |
0.49 |
0.93 |
|
BAHIA BLANCA AE |
-38.7 |
297.8 |
1860 |
0.48 |
0.91 |
|
MONTEVIDEO |
-34.9 |
303.8 |
1883 |
0.47 |
0.89 |
|
BUENOS AIRES |
-34.6 |
301.5 |
1858 |
0.51 |
0.94 |
|
NEUQUEN |
-39.0 |
291.9 |
1916 |
0.45 |
0.90 |
|
TRELEW |
-43.2 |
294.7 |
1916 |
0.41 |
0.85 |
Table 1. Stations used for the SAM index calculation grouped in four regions. The position, start year, correlation with the monthly SAM index and the correlation with the regional averaged pressure anomaly are given.
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