Relationship of Island and Offshore Diurnal Rainfall Over Sumatra

Predictability of onshore and offshore rainfall patterns across the Maritime Continent has long been a challenge for numerical models. This is largely due to the insufficient understanding how synoptic and mesoscale features interact to create conditions favorable for offshore- or onshore-migrating convective systems in this region. Hovmöller diagrams using observational data from two Years of the Maritime Continent (YMC) campaign periods (Pre-YMC and YMC 2017) have been constructed and utilized to understand propagation speeds of these systems as well as finding the trend of rainfall enhancement over land in the early afternoon and offshore in the late evening/overnight. Initial findings show that the rainfall is enhanced only over land or offshore, but never both within this sampling period. Ongoing work is underway to understand what causes this relationship and why these regions of rainfall are never enhanced at both times in the same event. This is one segment of our overall goal to analyze the potential propagation mechanisms for these events, including land-sea breeze effects, effects of gravity waves, and thermodynamic features such as moisture and upper-level winds.