Land‐Atmosphere Coupling Contributing to Anomalous Rainfall Before the Onset of Australian Monsoon

Abstract

This study applies idealized climate model simulations to investigate the influence of a continent‐sized ponded surface of limited heat capacity on the regional and remote atmospheric state. The analysis focuses on the wet season in northern Australia where precipitation provides critical water resources for agriculture and inland ecosystems. Model results show that the most significant precipitation change occurs before the onset of the Australian monsoon, which cannot be explained by the conventional “sea breeze” monsoon model. We use the moist static energy (MSE) budget to examine the underlying mechanism. When the Australian continent is turned into a large shallow lake, the increased latent heat flux contributes to increased net energetic forcing and export of MSE. As a result, wetting the land surface strengthens moisture convergence and divergence of dry static energy, demonstrating a top‐heavy atmospheric structure associated with deep convection. This study concludes that increased surface water availability in Australia strongly enhances pre‐monsoon precipitation via intensified land‐atmosphere coupling. This asymmetric response reflects the differing controls on rainfall across the wet season: pre‐monsoon rainfall over northern Australia is more strongly influenced by local land‐atmosphere coupling and synoptic‐scale processes, whereas rainfall during the mature monsoon is dominated by large‐scale oceanic convection and remote drivers of variability, including interactions with the ocean surface. Because the land surface perturbation imposed here primarily alters land surface fluxes while leaving oceanic processes unchanged, its impact is strongest prior to monsoon onset and weaker during the monsoon period.