Indonesian Maritime Continent has the second longest coastline in the world, but the characteristics of offshore rainfall and its relation to coastline type are not clearly understood. As a region with eighty percent being an ocean, knowledge of offshore rainfall is important to support activity over oceans. This study investigates the climatology of offshore rainfall based on TRMM 3B42 composite during 1998-2015 and its dynamical atmosphere which induces high rainfall intensity using WRF-ARW. The result shows that concave coastline drives the increasing rainfall over ocean with Cenderawasih Bay (widest concave coastline) having the highest rainfall offshore intensity (16.5 mm per day) over Indonesian Maritime Continent. Monthly peak offshore rainfall over concave coastline is related to direction of concave coastline and peak of diurnal cycle influenced by the shifting of low level convergence. Concave coastline facing the north has peak during northwesterly monsoonal flow (March), while concave coastline facing the east has peak during easterly monsoonal flow (July). Low level convergence zone shifts from inland during daytime to ocean during nighttime. Due to shape of concave coastline, land breeze strengthens low level convergence and supports merging rainfall over ocean during nighttime. Rainfall propagating from the area around inland to ocean is approximately 5.4 m/s over Cenderawasih Bay and 4.1 m/s over Tolo Bay. Merger rainfall and low level convergence are playing role in increasing offshore rainfall over concave coastline.
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机译：印尼海事大陆拥有世界上第二长的海岸线，但人们尚不清楚海上降雨的特征及其与海岸线类型的关系。作为一个百分之八十的海洋区域，了解近海降雨对于支持海洋活动至关重要。本研究调查了1998-2015年基于TRMM 3B42复合材料的近海降雨气候及其使用WRF-ARW诱发高降雨强度的动态大气。结果表明，凹形海岸线带动了整个海洋降雨的增加，其中Cenderawasih湾（最宽的凹形海岸线）的离岸强度最高（每天16.5mm），是印度尼西亚海域的最高。凹陷海岸线每月海上峰值降水量与凹陷海岸线的方向和昼夜周期峰值受低层辐合移动的影响有关。面对北方的凹形海岸线在西北风季风期间（3月）达到峰值，而面对东方的凹形海岸线在复活节风季风期间（7月）达到峰值。低层汇聚区白天从内陆转移到夜间海洋。由于海岸线呈凹形，陆风加强了低层汇合，并在夜间支持海洋上的降雨合并。从内陆周围地区到海洋的降雨在Cenderawasih湾上约为5.4 m / s，在Tolo湾上约为4.1 m / s。合并降雨和低水准收敛在增加凹形海岸线上的近海降雨中起着作用。
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