Study of The Impact of Convectively Coupled Equatorial Kelvin and Rossby Waves on Rainfall Extremes in Sulawesi, Indonesia

Abstract

Abstract This study examined the impact of Equatorial Kelvin and Equatorial Rossby (ER) waves on rainfall extremes over Sulawesi Island, Indonesia. Impacts are assessed by changes in the probability of rainfall events that exceeded extreme value and changes in the fraction of wet days. Using Asian Precipitation – Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) rainfall data and Outgoing Longwave Radiation (OLR) from NOAA, impacts are quantified with the respect to wave’s local phase grouping. The local wave phase is based on the standardized OLR anomalies and their temporal tendency. Results showed that Kelvin and ER wave can modulate daily rainfall extremes over Sulawesi Island. Kelvin wave has the strongest impact with changes in the probability of extreme rainfall by up to +100% (-70%) in phases 5 and 6 (1 and 2) and increases the value of wet day fraction by up to > 0.04. Followed by the ER wave with changes in the probability of extreme rainfall by up to +50% (-50%) in phase 4 (1 and 2) and increases the value of the wet day fraction by up to 0.05. The superposition between ER and Kelvin wave occurrence increases the possibility of extreme rainfall occurrence by up to 100 % in almost every part of Sulawesi island in phases 4,5 and 6. The results suggest that Kelvin and ER waves can be another important source of predictability for extreme rainfall on Sulawesi Island.