The Offshore Propagation of Convection From a Tropical Island: Mechanisms and Sensitivity

The diurnal cycle of convection is one of the most fundamental modes of climate variability in the tropics. Despite all the research that has been conducted on this topic, a deep understanding of this phenomenon remains elusive, which results in significant biases in global climate models. The challenges of representing the diurnal cycle are particularly egregious near tropical islands, where the complex interaction between land, ocean, and atmospheric processes leads to extensive offshore propagation of convection. Despite extensive observations, a comprehensive understanding of the underlying physical mechanisms and potential upscaling effects remains elusive.

Here, we approach this problem from a modeling perspective using a series of idealized simulations. Leveraging observational soundings from the Years of the Maritime Continent (YMC) field campaign, we employ a cloud-resolving model to simulate the offshore propagation of convection perpendicular to the coastline of an idealized island. This work simulates an offshore propagating mesoscale system and explores the fundamental processes and sensitive environmental dynamic and thermodynamic factors that significantly impact offshore propagation. Our findings indicate that high sea surface temperatures and initial low-level wind are necessary conditions for long-distance offshore propagation, and high-level wind accelerates the propagation. Precipitation-driven cold pools are identified as the primary dynamic source for the propagation speed over the ocean, while gravity waves generated on the second day tend to slow down the propagating convective system.