1997 Articles

Circulation changes and teleconnections between glacial advances on the west coast of New Zealand and extended spells of drought years in South Africa

Tyson, Peter; Sturman, Andrew; Fitzharris, Blair; Mason, Simon J.; Owens, Ian

Twentieth century changes in the terminal position of the Franz Josef Glacier on the west coast of New Zealand are compared with an area‐averaged mean annual rainfall series for the summer rainfall region of South Africa. Distinctive teleconnections are evident in an out‐of‐phase relationship between the two series, each of which exhibits an oscillation of 18–20 years. Periods of glacial advance are shown to coincide with extended dry spells in South Africa, when drought years are prevalent.

Reconstructed pressure anomaly fields are presented for periods of advance and recession of the glacier and for the inter‐decadal wet and dry spells in South Africa. In both cases major regional atmospheric circulation adjustments take place in a quasi‐regular fashion over time to produce an enhancement in westerly airflow during the periods of drought in Africa and glacial advance on the west coast of New Zealand. Extended wet periods and glacial recession are likewise shown to be associated with an enhancement of easterly components of the circulation. Changes in precipitation, temperature and moisture transport are examined and associations with the Southern Oscillation Index are investigated.

Franz Josef glacial advances are shown to occur 4–5 years after the onset of enhanced south‐westerly airflow on to the west coast of New Zealand. Advances occur on average 4 years after the onset of extended dry spells in South Africa. Similar atmospheric circulation anomalies in the respective sectors of the Southern Hemisphere and adjustments in the locations of the positions of the ridges in standing wave three are responsible for this correspondence.