TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 65 (No. 1), pp. 53-60, 2009

The Southern Annular Mode and Opposite-Phased Basin Mode of the Southern Ocean Circulation

Yuji Iijima1*, Shigeru Aoki2 and Kunio Kutsuwada3

1Graduate School of Environmental Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan
2Institute of Low Temperature Science, Hokkaido University, Kita-ku, Sapporo 060-0819, Japan
3School of Marine Science and Technology, Tokai University, Orido, Shimizu-ku, Shizuoka 424-8610, Japan

(Received 1 August 2007; in revised form 25 July 2008; accepted 25 July 2008)

Abstract: Over the Southern Ocean the dominant modes of the atmospheric field are known as the Southern Annular Mode (SAM) or Antarctic Oscillation, and the Pacific South American (PSA) pattern. Statistical analysis of sea surface wind (SSW) from satellite observation revealed two leading modes of SAM-like and PSA patterns. In the high latitudes, the SAM-like pattern of the SSW had a large amplitude over the Bellingshausen Basin and Australian-Antarctic Basin, with opposite phase between the two basins. On the intraseasonal time scale, large-scale sea surface height (SSH) also had notable variability, showing a basin-scale anti-phase mode over the two basins. To explain the response of oceanic variations to these atmospheric modes, we analyzed the relationship between the dominant modes of wind stress and large-scale SSH on the intraseasonal time scale. The SAM-like pattern of wind stress was correlated with the SSH variation over the two basins. The SSH basin mode was most simply explained by a simple barotropic response to the SAM-like mode of wind stress, with the curl of opposite phase between the two basins. We conclude that the zonal asymmetry of the wind field of the SAM plays an important role in driving the anti-phase SSH basin modes.

*Corresponding author E-mail: i-yu-ji@lowtem.hokudai.ac.jp

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