Half-century seasonal relationships between the Southern Annular Mode and Antarctic temperatures

In this short communication we examine the relationship between the Southern Hemisphere Annular Mode (SAM) and Antarctic near-surface temperatures using data from Antarctic stations for 1957-2004. This near half-century period is significantly longer than analysed in previous studies. Furthermore, the four seasons are considered independently while the longer datasets allow the temporal stability of the relationship to be investigated. A general pattern of positive (negative) correlations between the strength of the SAM and temperatures in the northern Antarctic Peninsula (East Antarctica) is shown to be valid for the last half century but detailed differences are established between the seasons. These include a seasonal change in the sign of the relationship at one station, while at others there are single seasons when temperatures there are or, in some cases, are not significantly related to the SAM. Generally, SAM-temperature correlations are stronger across Antarctica in austral autumn and summer. Estimates of the contribution that trends in the SAM have made to Antarctic near-surface temperature change between 1957 and 2004 are greatest in autumn: in this season they exceed 1°C at half the 14 stations examined with a maximum change of –1.4°C. There does not appear to have been any significant long-term change in the strength of SAM-temperature relationships over the period examined, even with the onset of ozone depletion. However, on an annual basis, the long-term relationship between the SAM and near-surface temperatures can be disrupted and even reversed at some stations although coastal East Antarctica appears stable in this respect. These findings give support to the exploitation of appropriate ice core data to determine longer-term changes in the SAM based upon transfer-functions derived from recent data.

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