The Impact of Concave Coastline on Rainfall Offshore Distribution over Indonesian Maritime Continent.

Furqon Alfahmi,Rizaldi Boer,Ardhasena Sopaheluwakan,Rahmat Hidayat,Perdinan Perdinan

doi:10.1155/2019/6839012

Abstract

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.

Highlights

Indonesian Maritime Continent (IMC) is an archipelago tropical country which has the second longest coastline in the world after Canada
Sea breeze raises up convergence zone over a convex coastline and divergence zone over concave coastline
Upward movement of air induced by convergence zone fostering the development of clouds brings out high rainfall intensity over coastline [4, 5]

Summary

Introduction

Indonesian Maritime Continent (IMC) is an archipelago tropical country which has the second longest coastline in the world after Canada. Distribution of global and regional rainfall is affected by IMC’s coastline. The distribution of local rainfall amount (a rainfall point less than 300 km from coastline) is a gradually decreasing as function of coastal distance, while total regional rainfall (rainfall area more than 10,000 km2) is increasing as function of coastline density (coastal length/land area) [1]. There are three shapes of coastline which affect the rainfall amount, straight coastline, concave coastline, and convex coastline [2, 3]. Sea breeze raises up convergence zone over a convex coastline and divergence zone over concave coastline. Land breeze creates convergence over convex coastline and divergence zone over a concave coastline. Upward movement of air induced by convergence zone fostering the development of clouds brings out high rainfall intensity over coastline [4, 5]

Methods

Results

Conclusion