The Impact of Orographically-Induced Gravity Waves on the Diurnal Cycle of Rainfall over Southeast Kalimantan Island

Abstract

Precipitation measurements from the Tropical Rainfall Measuring Mission (TRMM) satellite indicate that the southeastern area of Kalimantan (Borneo) Island receives much less rainfall than elsewhere on the island during the period from July to October. Results from sur- face meteorological observations show that the diurnal cycle of rainfall differs greatly between the eastern and western coasts of the island. Rainfall on the western coast of the island is frequent in the afternoon and evening, whereas almost all rainfall on the eastern coast occurs in the morning. Meanwhile, the Global Positioning System (GPS)-derived precipitable water (PW) on the eastern coast shows a substantial decrease in moisture in the af- ternoon and evening. Numerical experiments with a mesoscale model reveal that gravity waves driven by di- urnal heating of the elevated land surface of the moun- tains on Sulawesi Island, which lies approximately 300 kilometers to the east of Kalimantan Island, significantly affect the diurnal cycle of rainfall over southeast Kali- mantan Island. Keywords: diurnal cycle, rainfall, precipitable water, Kalimantan (Borneo) Island, gravity wave Citation: Wu, P., J. I. Hamada, M. D. Yamanaka, et al., 2009: The impact of orographically-induced gravity waves on the diurnal cycle of rainfall over southeast Ka- limantan Island, Atmos. Oceanic Sci. Lett., 2, 35−39.