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].

Acknowledgments: This work is supported by funding from the National Science Foundation.

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, 22, 5319-5345, doi: 10.1175/2009JCLI2785.1. Full Text (PDF)
  • Fogt, R. L., J. Perlwitz, A. J. Monaghan, D. H. Bromwich, J. M. Jones, and G. J. Marshall, 2009: Historical SAM Variability. Part II: 20th century variability and trends from reconstructions, observations, and the IPCC AR4 Models. J. Climate, 22, 5346-5365, doi: 10.1175/2009JCLI2786.1. Full Text (PDF)


    CONTACTS: Ryan L. Fogt (fogtr@ohio.edu)



    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



    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
    

    Last Revised May 4, 2012