Evaluasi Skema Konveksi dalam Model Iklim Regional RegCM4 untuk Simulasi Keragaman Curah Hujan Musiman dan Intra Musiman di Indonesia

Abstract

RegCM4 simulations for Indonesia based on two different convective schemes (MIT and Grell) have been done in this study. The simulations were conducted for two consecutive years between 1998 and 1999 periods for Indonesia. Two different convective schemes were evaluated based on their ability in simulating seasonal and intraseasonal rainfall variability in the region. The modeled seasonal rainfall were analyzed through their comparisons with satellite-based rainfall observation data from TRMM. The results show that the MIT-based rainfall simulation produced higher rainfall mostly over mountainous regions and lower rainfall in some other areas over Indonesia compared to the observation. Differently, the Grell scheme underestimated rainfall over almost all areas in the country. In analysis of monthly rainfall, Grell could describe monsoonal and equatorial pattern of monthly rainfall in Cengkareng and Pontianak station better than MIT. MIT couldn’t describe monsoonal and equatorial pattern of Cengkareng and Pontianak rainfall which are located in low land. Despite its tendency of being more sensitive over mountainous areas, MIT was found to be better in simulating the seasonal cycle of rainfall than Grell. In order to ilustrate intraseasonal variability of rainfall, MJO was used as the case reference. Principal component analysis of TRMM, MIT, and Grell were calculated and analyzed in order to detect MJO phases. This was done by comparing the PC results with RMM Index. The output of MIT and Grell Schemes can well recognize MJO signal by giving higher rainfall value on the MJO events affecting the region. However, it has not known yet which better scheme could be used in ilustrating intraseasonal rainfall variability, because the PCA time series of MIT and Grell still have another cycle beside of MJO cycle. MIT scheme consider to be more dominant in describing intraseasonal rainfall variability based on the higher PCA’s percentage of variant. As a whole of this study, MIT was found better in representing Indonesian Rainfall Variability than Grell. Thus, MIT scheme can be used in other simulations of RegCM4 on Indonesian Climate Studies