Convection in the tropics is comprised of multi-scale quasi-periodic structures ranging from the Madden-Julian Oscillation, convectively-coupled waves, down to land and sea breezes initiated along complex coastlines. In the maritime continent, especially, the diurnal cycle is a prominent feature of the convective cloud and precipitation distributions. In addition to the afternoon peak in convective activity over land, many adjacent oceanic regions have a secondary nocturnal or early-morning precipitation maximum. While parts of this secondary maximum can be linked to land breeze circulations, other prominent offshore propagating disturbances are linked to gravity waves. However, many aspects of the dynamics of these processes and their regional variation are poorly understood. They also have broader implications in that most numerical models with parameterized convection have difficulty reproducing the timing of the daytime peak in convective activity and the occurrence of the secondary maximum.

Here we summarize progress over the last few decades in the understanding of gravity waves and their role in the diurnal cycle of convection in the tropics, including the mechanisms underlying the gravity wave source. We also present recent results using large-domain convection-permitting model simulations over the maritime continent to diagnose the gravity waves and their influence. These simulations demonstrate that diurnally-forced offshore-propagating gravity waves play a dual role: (1) they destabilize the environment to promote the longevity of pre-existing offshore-propagating convective systems; and (2) they initiate convection significant distances offshore. The simulations also demonstrate that daytime moist convection makes a critically important contribution to the gravity wave generation, alongside the diurnal heating/cooling of the mountainous island terrain.

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*email: tplane@unimelb.edu.au
*Preference: Invited