Modelling the winds on days of high ozone in Perth

In summer, the coastal city of Perth, Western Australia is influenced mainly by easterly synoptic winds, with strong southwesterly sea breezes dominating during the afternoon period. In this paper we use both data analysis and mesoscale meteorological modelling to reveal the major meteorological mechanisms conducive to high ozone levels in the region. Analysis of the data revealed that practically all high-ozone days appear to be associated with recirculation of ozone or its precursors over the Perth area. Numerical modelling points to both same-day and next-day recirculation of surface air over the Perth region in easterly synoptic flow as being conducive to high ozone levels. An hydraulic jump effect over the nearby escarpment is both observed and predicted under moderate easterly synoptic flow. The locally well known West Coast Trough produces southeasterly surface flow off the coast of Perth, and the modelling in this study has confirmed that the trough is caused mainly by differential heating between the land and sea.