Seasonal Southern Hemisphere Annular Mode (SAM) Reconstructions

OVERVIEW:

The dominant mode of climate variability across the Southern Hemisphere is the Southern Hemisphere Annular Mode (SAM), which has been associated with warming in the Antarctic Peninsula and a weak cooling across the remainder of the continent (Marshall 2007). Fundamentally, the SAM is an expression of the meridional pressure gradient between the sub-Antarctic and middle latitudes. The mode has been increasing towards its positive polarity (in the annual, summer, and autumn means) since the late 1960s, leading to lower (higher) surface pressures over Antarctica (southern mid-latitudes). A number of modeling studies attribute these recent positive trends to stratospheric polar ozone depletion and increasing greenhouse gas concentrations, while natural forcing mechanisms (such as solar, volcanic, or internal climate processes arising from tropical sea surface temperature variability) may also be playing a role (see Fogt et al. 2009 and references therein).

Despite the significance and importance of these recent trends, little is known of historical SAM variability as reliable SAM indices only extend back until 1957. Thus, it is difficult to separate the contributions of natural and externally-forced fluctuations in driving the recent trends, given the knowledge gap of natural SAM fluctuations prior to the last 50 years. To accomplish this goal, long-term reliable SAM indices are required.

Using the methodology (i.e., principal component regression) of previous studies (see Jones et al. 2009 and references therein), SAM reconstructions have been obtained for all seasons using only observed pressure records across the Southern Hemisphere. A cross-validation procedure was used to determine the robustness of each reconstruction (Jones et al. 2009), and these statistics are given below. The reconstructions listed here are calibrated to the Marshall (2003) observationally-based SAM index as outlined in Jones et al. (2009). However, the reconstructions here are adjusted slightly so that the mean over 1971-2000 is zero, as in the Marshall (2003) index. Indices created by Dr. Julie Jones calibrated to ERA-40 principal component 1 are housed at a different location [TBD].

RELEVANT PUBLICATIONS:

Jones, J. M., and M. Widmann, 2003: Instrument-and tree-ring estimates of the Antarctic Oscillation. J. Climate, 16, 3511-3524.

Marshall, G. J., 2003: Trends in the Southern Annular Mode from observations and reanalyses. J. Climate, 16, 4134-4143.

Jones, J. M., and M. Widmann, 2004: Atmospheric science - Early peak in Antarctic Oscillation index. Nature, 432, 290-291.

Marshall, G. J., 2007: Half-century seasonal relationships between the Southern Annular Mode and Antarctic temperatures. Int. J. Climatol., 27, 373-383.

Visbeck, M., 2009: A station-based Southern Annular Mode index from 1884 to 2005. J. Climate, 22, 940-950.

Jones, J. M., R. L. Fogt, M. Widmann, G. J. Marshall, P. D. Jones, and M. Visbeck, 2009: Historical SAM Variability. Part I: Century length seasonal reconstructions. J. Climate, in press. PDF preprint

Fogt, R. L., J. Perlwitz, A. J. Monaghan, D. H. Bromwich, J. M. Jones, and G. J. Marshall, 2009: Historical SAM Variability. Part II: 20^th century variability and trends from reconstructions, observations, and the IPCC AR4 Models. J. Climate, revised. PDF preprint

CONTACTS: Ryan L. Fogt (ryan.fogt@noaa.gov)

NOTE: Reconstructions updated March 2008 using slightly different calibration methodology. Reconstruction statistics also reflect these changes.
Annual mean reconstructions are also available, but are not published. Please contact Ryan Fogt at above email for information about obtaining these data.

RECONSTRUCTION METADATA

Station Statistics Plots of Station Beta Weights
(with ERA-40 MSLP / SAM correlation 1979-2001) Reconstruction Statistics
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON
DJF
MAM
JJA
SON

Station Statistics	Plots of Station Beta Weights (with ERA-40 MSLP / SAM correlation 1979-2001)	Reconstruction Statistics
DJF MAM JJA SON	DJF MAM JJA SON	DJF MAM JJA SON

DATA

Click here to download the below data in ascii format (-999.9 is missing). DJF values are defined based on the year of the December. (i.e., DJF 1900 = December 1900, January-February 1901).

         DJF     MAM     JJA     SON

1865    0.088  -1.740  -999.9  -999.9
1866    0.937   0.726  -999.9  -999.9
1867   -2.675   1.564  -999.9  -999.9
1868   -1.724  -0.246  -999.9  -999.9
1869   -2.429  -0.649  -999.9  -999.9
1870   -0.469   0.441  -999.9  -999.9
1871   -0.438  -0.185  -999.9  -999.9
1872    0.391   0.496  -999.9  -999.9
1873    1.203  -0.524  -999.9  -999.9
1874   -0.510   1.746  -999.9  -999.9
1875    0.307  -0.245  -999.9  -999.9
1876   -0.682  -1.495  -999.9  -999.9
1877    1.339  -1.848  -999.9  -999.9
1878   -0.839  -1.473  -999.9  -999.9
1879   -0.832   1.642  -999.9  -999.9
1880    0.290   0.479  -999.9  -999.9
1881   -2.604   0.937  -999.9  -999.9
1882    0.647  -0.765  -999.9  -999.9
1883   -1.909   0.198  -999.9  -999.9
1884   -2.034   2.657  -999.9  -999.9
1885    1.029  -0.178  -999.9  -999.9
1886    0.115  -0.489  -999.9  -999.9
1887    0.112   0.427  -999.9  -999.9
1888    0.825  -1.181  -999.9  -999.9
1889   -2.173   0.780  -999.9  -999.9
1890   -0.272   3.018  -999.9  -999.9
1891   -1.621   2.454  -999.9  -999.9
1892   -0.239   2.583  -999.9  -999.9
1893    0.317   0.302  -999.9  -999.9
1894    2.477   0.245  -999.9  -999.9
1895   -0.960   0.129  -999.9  -999.9
1896    0.699  -0.391  -999.9  -999.9
1897   -2.276  -2.991  -999.9  -999.9
1898   -0.668  -1.519  -999.9  -999.9
1899   -1.125  -1.324  -999.9  -999.9
1900    0.119  -0.460  -999.9  -999.9
1901   -2.468  -1.014  -999.9  -999.9
1902   -2.457  -1.835  -999.9  -999.9
1903   -0.444  -1.464  -999.9  -999.9
1904    0.215   0.390  -999.9  -999.9
1905    0.322   0.155   0.572   0.779
1906    0.176  -2.458  -0.915   0.574
1907    1.622  -0.148  -0.237  -1.705
1908    0.191  -0.706  -0.249  -0.013
1909    0.315  -0.758  -0.193   0.708
1910    0.086   0.733  -2.800   0.043
1911   -3.867   0.471   2.989  -0.920
1912   -0.849   0.644   0.276  -1.872
1913    0.819  -0.966  -1.000  -0.232
1914   -0.777  -0.293   0.277   3.035
1915   -0.221  -1.300  -0.359  -4.667
1916   -0.424  -0.599  -1.924   0.073
1917    0.572   0.259  -2.150  -0.821
1918   -0.655  -0.966  -1.670  -2.028
1919    1.115   0.309   0.723   0.574
1920    0.982  -1.268   0.134  -0.178
1921    0.961   0.057  -1.083  -0.684
1922   -2.424  -1.589   1.114  -0.454
1923   -0.680  -1.603  -2.673  -1.557
1924   -0.885   0.139   0.644  -0.413
1925   -3.246   0.565   0.984  -1.049
1926   -0.681  -0.170  -0.125  -2.173
1927    3.252  -1.289   0.825   0.170
1928   -2.527   0.030  -0.309  -3.087
1929   -2.900   0.045   0.313   1.002
1930   -1.485   2.568   0.716  -1.832
1931   -1.019   2.549  -0.122  -0.860
1932   -2.289   1.164  -0.710   2.766
1933    1.396  -0.957   1.847   2.109
1934    1.188   2.392   1.983   1.165
1935    1.452  -1.104  -1.318   0.958
1936   -1.502  -0.533   0.571  -1.104
1937    1.395  -1.447   1.882   2.164
1938   -3.817   0.750   2.688   1.060
1939   -2.945   2.623  -3.703   1.406
1940    1.362  -1.916   3.408  -0.309
1941   -0.952  -0.307  -0.490  -0.735
1942   -1.022   0.568   0.858  -3.163
1943    1.222   0.078  -0.454   1.863
1944   -1.755  -0.168  -0.358  -3.254
1945   -1.905  -2.068  -0.171  -0.980
1946   -1.718  -0.248  -1.715  -1.215
1947    0.139   1.839  -1.448   0.972
1948   -2.565  -1.447   0.591  -1.705
1949   -3.153   0.879  -0.414   1.569
1950    0.584   0.340   1.745   1.555
1951   -1.342  -1.727   0.254  -2.107
1952    1.058  -1.808  -0.323   0.568
1953   -0.004  -1.206   0.654  -0.822
1954   -0.189  -1.497  -0.348   1.073
1955    0.024  -0.362  -1.182  -0.889
1956   -1.856  -1.200  -3.512   0.452
1957   -1.328  -1.734  -0.053  -2.066
1958    1.572  -2.070  -0.452   2.064
1959   -0.395  -0.374   0.561   2.679
1960    1.588  -0.063   1.357   1.939
1961    2.695   0.347   0.683   3.044
1962    3.157   0.077  -1.094  -1.407
1963   -0.263   0.546  -1.503   0.265
1964   -3.955   0.779  -4.077  -2.216
1965   -0.237  -1.351  -0.146   1.345
1966   -1.184  -1.443   1.051   1.809
1967   -0.638   0.259   1.860   0.608
1968   -0.450  -1.827  -0.316  -3.337
1969    0.650  -1.691   1.012   2.103
1970   -0.237  -1.988  -0.279  -1.259
1971   -1.118  -0.613   0.460  -2.002
1972   -0.354  -1.960  -2.177  -0.200
1973    1.550  -2.040   1.794  -1.150
1974   -0.688   1.733  -3.644   1.198
1975   -0.636  -1.662  -1.722   0.464
1976   -3.167   0.585   1.060   0.616
1977    1.654  -2.161   0.399   0.810
1978   -0.133   0.553  -0.419   0.814
1979   -2.216   0.108   2.614   0.233
1980    0.893  -1.453  -0.185  -2.391
1981    0.139   0.002  -1.585  -0.046
1982   -2.227   0.556   1.408   0.104
1983   -0.699  -1.284   0.838   0.657
1984   -1.805  -0.573   0.951  -0.698
1985   -1.368   1.178   1.061   1.562
1986   -0.486  -1.010  -0.186   0.870
1987   -0.193   0.050   0.786  -0.469
1988    0.150   1.574  -1.456  -2.582
1989    0.716   2.044   1.214   1.679
1990   -1.030  -1.827   0.349   2.734
1991   -1.018  -0.413  -1.632  -1.981
1992    0.643   0.482  -2.689   1.088
1993    0.594   0.562   2.154   1.285
1994    2.390  -0.758   0.018  -1.968
1995    0.767  -0.289  -2.144   0.692
1996    0.738   0.439  -1.572  -1.906
1997    1.365   0.853   1.571  -0.303
1998    2.858   0.729   2.609   0.615
1999    2.664   2.740   0.132   1.942
2000    0.027   1.847   0.002  -1.670
2001    1.015   1.686   1.583   1.485
2002    1.657  -0.943  -1.933  -3.352
2003    0.139   2.644   1.767  -0.555
2004   -0.488   1.072   0.018  -0.047
2005   -999.9   0.983  -0.047  -0.848

Page maintained by Ryan L. Fogt. Comments or suggestions should be sent to ryan.fogt@noaa.gov.

Last Revised March 31, 2009