MODIS Land Data Operational Product Evaluation (LDOPE) software toolsEntry ID: LDOPE
Abstract: 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].
Credit: Ryan L. Fogt and Byrd Polar Research Center.
Data Set Citation
Dataset Originator/Creator: Ryan L. Fogt
Dataset Title: Seasonal Southern Hemisphere Annular Mode (SAM) Reconstructions 1979-2001Online Resource: http://polarmet.osu.edu/
Start Date: 1979-06-01Stop Date: 2001-08-31
ISO Topic Category
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.
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, revised.
Creation and Review Dates
DIF Creation Date: 2010-10-14
Last DIF Revision Date: 2012-02-15