A climatology of coastal ridging over south-eastern Australia

Abstract

The dominant feature of sea-level pressure (SLP) patterns over the coastal regions of south-eastern Australia is the ridging that extends northwards along the coast. This ridging is particularly evident in the warmer months, October to March, when it is present on part or all of approximately 65 per cent of days, usually occurring in sequences ranging from one to several days. In this paper, three distinct forms of coastal ridging are identified, and are referred to as types 1, 2 and 3. Their distinguishing synoptic and subsynoptic characteristics are described. As well as their ubiquity and synoptic significance, all three types are important because each can generate severe weather of the following types: heavy precipitation, strong winds, or sudden changes in wind direction and temperature. Climatologies of the three types are prepared for the 20-year period 1974-1993 in the form of both monthly and annual frequencies of occurrence. Given that south-eastern Australia is one of the areas of the globe most affected by the El Niño-Southern Oscillation (ENSO), correlations are calculated between monthly ridging frequencies and monthly values of the Southern Oscillation Index (SOI). Also, annual frequencies are correlated with the annual (January to December) SOI value. Three diagnostic case studies are presented in considerable detail because they are very important to understand thoroughly the nature of and differences between the three types of ridging. ©1997 by the Royal Meteorological Society.