A synoptic climatological evaluation of the changes in the CSIRO nine‐level model with doubled CO2 in the New Zealand region

Abstract

AbstractA synoptic climatological evaluation of the output of the CSIRO nine‐level model shows differences from the climatology derived by Kidson from ECMWF analyses for 1980–1988. The model climatology includes more days with winds from the westerly quarter, and fewer anticyclones are found to the south and south‐east of New Zealand. The difference in climate between the single and doubled CO2 runs was relatively small using the synoptic classes derived from the ECMWF analyses, and an alternative set of daily classifications was obtained from the model data.Significant differences between the single and doubled CO2 runs were then apparent, particularly in the winter season. The number of highs to the west of New Zealand decreased and both cyclonic and anticyclonic south‐west flow on to the country increased. Mean departures in the climatic elements were obtained for days in which a good match was obtained between the model‐derived synoptic classes and ECMWF analyses. These suggested that more rain should fall on the south and west of the country with increasing CO2. Relative to the overall warming trend, minimum temperatures may be a little higher in the central and western North Island and maximum temperatures lower in the south of the South Island and higher in the east of the North Island. Bright sunshine may decline slightly, and more wind is expected over the North Island.