New Zealand climate: The impact of major volcanic eruptions
Major volcanic eruptions which inject significant amounts of dust and sulphate aerosols into the atmosphere produce discernible climate signals in the New Zealand region. A superimposed epoch (compositing) method was used to determine the effects on regional temperatures of the six major volcanic eruptions since the 1880s that have been likely to have affected New Zealand climate. Regional atmospheric circulation anomalies during the three significant late twentieth century volcanic eruption events were examined. As El Nino – Southern Oscillation (ENSO) events significantly affect temperature and circulation anomalies, these climatic effects were removed. The results show that the effects on temperature and atmospheric circulation in the New Zealand region commenced rapidly, in the first few months after the volcanic eruption event, and lasted 24 months. These events were found to depress surface temperatures in the region by 0.3 to 0.4 C from 1 to 21 months after the eruption. Atmospheric circulation anomaly patterns were very distinct and show more surface southerlies and troughs near the Chatham Islands in the first two seasons (1 - 6 months) after the eruption, followed by stronger west to south west flow anomalies in seasons three to five (7 to 15 months) over the region. Finally, a period of more troughs over the North Island of New Zealand occurs in seasons six to eight (16 to 24 months) after the eruption episode. The magnitude of the volcanic signal in the New Zealand region is consistent with previous larger-scale global studies.