Nested Coupled Air/sea Modeling for Multi-scale Processes in the Maritime Continent

We have conducted simulations of the western Pacific region utilizing high-resolution nested coupled air/sea modeling. Our 3-km resolution COAMPS results are compared with observations on land, at sea and by satellite. The confluence of several factors operating at multiple scales created a winter of extreme precipitation in the Philippines in 2008. These factors included: a moderately strong La Nina, a neutral to negative Indian Ocean Dipole, northeast monsoon conditions with strong synoptic monsoon surges, and intense MJO activity. On land, towns were evacuated due to rain-induced flooding of rivers emanating from mountainous regions. In the ocean, near-surface low salinity measured from a research vessel in adjacent coastal waters was attributed to freshwater run-off from the rivers draining the mountains. The 3-km model simulations revealed high precipitation in the mountains coinciding with peak MJO wet phase and monsoon cold surge episodes, and consistent with the interpretation of ocean measurements and ground-based reports. However rain gauges were not well situated to capture the rainfall signal in the mountains, and it is likely the model overestimated rainfall totals. The need for additional rain gauge and river discharge monitoring is highlighted as important aspects for the upcoming international Years of the Maritime Continent field and modeling campaign (2017-2019). Additional elements are being added to the COAMPS system that will be able to seamlessly represent the hydrological processes that are important in the multi-scale impacts documented in this study.