Components of precipitation and temperature anomalies and change associated with modes of the Southern Hemisphere

Abstract

AbstractA long simulation of climate by the CSIRO Mark 3 coupled atmosphere—ocean model is analysed to assess the role of three modes of the Southern Hemisphere (SH) circulation on the inter‐annual variability of precipitation and surface temperature and the contribution of the modes to patterns of change under global warming. Indices of El Niño‐southern oscillation (ENSO) and the high‐ and low‐latitude modes (HLM, LLM) of zonal mean zonal wind are extracted from monthly means during the period 1871–1970. The model El Niño brings mostly drier and warmer conditions to Australia—New Zealand (NZ), South America and southern Africa in both annual and seasonal means. The HLM and LLM modes impact rainfall and temperature in banded patterns. Positive HLM [which is closely related to the southern annular mode (SAM) in pressure] moistens and cools around 20–35°S particularly near the east coast of each continent. Farther south it mostly dries and warms, especially in the austral winter. The LLM has some impacts, including increased summer rain in western Australia, and temperature anomalies in eastern South America in autumn. Mostly similar patterns are found in the ERA40 observational data. Changes in the indices in the 22nd century, following warming forced by the A1B greenhouse gas (GHG) scenario, are positive, in most cases, and similar in magnitude to their inter‐annual variability. The drying and warming of Australia associated with an El Niño‐like change are largely countered by the HLM‐like change, and similar effects are seen in parts of the other continents. The far south of NZ and South America are dried and warmed by the HLM change, but these relative changes are countered by non‐modal effects in the Southern Ocean. Overall the impact of the simulated modes is largest on Australia, with the HLM being as important as ENSO in the mid‐latitudes. Copyright © 2008 Royal Meteorological Society