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:
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