Slopes of glacier ELAs in the Southern Alps of New Zealand in relation to atmospheric circulation patterns

The links between climate and glaciers of the Southern Alps are investigated by examining the relationships between atmospheric circulation and glacier mass balance changes, as measured by end-of-summer snowlines (ELAs) over a 21-year period on 48 index glaciers. Trend surfaces are fitted to the ELAs data for each mass balance year, and the elevation and slope of each surface is computed. These are compared to atmospheric pressure anomaly maps generated for the southwest Pacific from long-period climate station data. The results show that atmospheric circulation patterns exert a strong control on elevation and slope of the trend surfaces. A simple “sloping roof” model is suggested to represent the ELAs surface, with its tilt across the Southern Alps varying from year to year, depending upon the nature of the atmospheric circulation. Steeper sloping trend surfaces across the Southern Alps are associated with anomalous southwest to westerly flow, whereas less steep slopes are associated with anomalous airflow from the south, southeast, and easterly directions.