Atmospheric circulation and monthly precipitation distribution in Canterbury, New Zealand
The relationship between atmospheric circulation and the distribution of precipitation over Canterbury is examined using monthly totals for 137 stations over the period 1961 to 1980. Monthly indices of atmospheric circulation based on daily isobaric maps are correlated with the precipitation totals. The generally weak but significant correlation coefficients exhibit a clearly organised spatial pattern, except for correlation with the southerly index. The influence of cyclonic isobaric curvature is greatest in the intermontane basins and southern parts of Canterbury, while westerly airflow produces a decline in monthly precipitation to the east and northeast. The map of correlations with easterly airflow shows the opposite precipitation gradient, but with more detail of the influence of Banks Peninsula on precipitation distribution. Stepwise regression was used to identify which circulation index was the best predictor of monthly precipitation for each station. The resulting map shows that the influence of westerly airflow is limited to the main divide of the Southern Alps, while cyclonicity is important for the intermontane basins, the eastern foothills, south Canterbury and around Banks Peninsula. Precipitation over the plains and northeast Canterbury is dominated by easterly airflow.