Wind-regime modulation of cloud, precipitation and sea surface heat budget: case studies over the central Great Barrier Reef

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Abstract
The Great Barrier Reef (GBR) is increasingly threatened by marine heatwaves and mass coral bleaching events, with local atmospheric conditions playing a critical role in modulating sea surface temperatures and heat stress. This study examines how synoptic-to-mesoscale meteorological processes shaped cloud formation, precipitation and the ocean surface heat budget across the central GBR during the 2021–22 austral summer. Using a combination of observations, reanalysis data and high-resolution convection-permitting simulations, two representative cases are analysed: a trade wind breakdown period associated with early-summer heating and a trade wind regime linked to mid-summer cooling. The breakdown case featured enhanced convective available potential energy, deep convection, greater upper-level moisture transport and heavier rainfall, while exhibiting reduced latent heat flux owing to weaker winds. By contrast, the trade wind case was characterised by shallow clouds, dry atmospheric conditions, stronger latent cooling and minimal rainfall. Mesoscale convective systems during breakdown periods generated temporally limited but spatially extensive increases in surface winds and turbulent heat fluxes, particularly near the coast where coral reefs are concentrated. These episodes contributed to localised cooling of the ocean surface, offering temporary relief from heat stress, with this effect not being captured in coarser reanalyses. This study highlights the crucial role of synoptic-to-mesoscale atmospheric variability in influencing the surface heat budget of the GBR and demonstrates the added value of high-resolution simulations in resolving mesoscale processes relevant to reef-scale heat stress. These findings have important implications for assessing coral bleaching risk under current and future climate conditions.

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