A CLIMATOLOGY OF COASTAL RIDGING OVER SOUTH-EASTERN AUSTRALIA

The dominant feature of sea-level pressure (SLP) patterns over the coa stal regions of south-eastern Australia is the ridging that extends no rthwards 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 rang ing from one to several days. In this paper, three distinct forms of c oastal ridging are identified, and are referred to as types 1, 2 and 3 . Their distinguishing synoptic and subsynoptic characteristics are de scribed. As well as their ubiquity and synoptic significance, all thre e 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 ar e prepared for the 20-year period 1974-1993 in the form of both monthl y and annual frequencies of occurrence. Given that south-eastern Austr alia is one of the areas of the globe most affected by the El Nino-Sou thern Oscillation (ENSO), correlations are calculated between monthly ridging frequencies and monthly values of the Southern Oscillation Ind ex (SOI). Also, annual frequencies are correlated with the annual (Jan uary to December) SOI value. Three diagnostic case studies are present ed in considerable detail because they are very important to understan d thoroughly the nature of and differences between the three types of ridging. (C) 1997 by the Royal Meteorological Society.