The nature of summer-time precipitation over north-western Australia

According to Bureau of Meteorology (BoM) statistics, summer-time (December-February) rainfall over north-western Australia has shown a significant positive trend over the last half-century. This research aims to identify the dominant physical mechanisms that regulate the spatio-temporal pattern of summer time rainfall in this region. This is accomplished using a combination of in-situ rainfall records, remote sensing platforms and numerical reanalysis products.

At the core of this research are long-term rainfall observations from four BoM climate stations, which lie along an 800-km line stretching south-eastwards across the Kimberley Plateau from the coast into the interior of the continent. These observations show that near the coast the diurnal cycle of rainfall is in phase with solar heating, whereas inland there is a distinct night-time maximum in rainfall amounts. Consistent with hypotheses from previous studies, composite synoptic structures from numerical reanalysis products indicate that this night-time peak coincides with maximum low-level convergence into the continental heat low. However, when the data are stratified by the occurrence of rainfall events, these composites reveal significant environmental differences exist prior to the onset of rainfall events. Further analysis suggests that these environmental differences tend to occur on synoptic timescales and are likely linked to the presence of transient synoptic features.