Relationship between rainfall and weather regimes in south-eastern Queensland, Australia

摘要

The present study aims to determine synoptic regimes associated with rain and no-rain days in south-eastern Queensland. A k-means cluster analysis is used on upper-air data from Brisbane Airport to identify dominant weather regimes for the region. Eight weather regimes appear to succinctly describe the main types of conditions experienced in south-eastern Queensland. Using rainfall data from 307 sites across the region, the rainfall associated with each weather regime is then characterized. Four of the regimes are associated with moist conditions; each accounts for about 15-20% of the mean total annual rainfall. These regimes preferentially occur during the summer and are characterized by high onshore moisture flux. The four dry regimes are characterized by southerly moisture flux and generally occur throughout the year. These regimes combined account for less than 25% of the mean total annual rainfall but more than 60% of the days in a year. Back trajectories at five levels were computed for each of the regimes using the HYSPLIT model. Case studies were selected for the four wet regimes and examined in detail. The wet regimes exhibit geographically shorter back trajectories, particularly at lower levels, than the dry regimes. In addition, there is usually a northerly component to the 500 m level trajectories close to Brisbane for the wet regimes.