Numerical Simulation of the Genesis of Cyclone Nargis Using a Global Cloud-System Resolving Model, NICAM

Abstract

We have been challenging the simulation of tropical cyclone (TC) geneses using a global/regional cloud-system resolving model (GCSRM), non-hydrostatic ICosahedral-grid atmospheric model (NICAM) (Satoh et al. 2008). A GCSRM has the advantages that it can deal with the organization of meso-scale cloud systems into a tropical cyclone during the cyclogenesis process, and that it can cover the long-distance movement of TC sources such as tropical waves. Using a GCSRM, our goal is to reveal the relation between predictabilities and mechanisms of TC geneses. In the previous studies, two important perspectives have been suggested related to TC geneses: environments and sources. The large-scale environments explain probability distribution of TC geneses including climatological seasonal change, interannual variability like ENSO, and intraseasonal oscillation such as Madden-Julian Oscillation. On the other hand, the precise timings of TC geneses seem to be triggered by synoptic-scale sources such as tropical waves, extratropical disturbances, and energy dispersions from neighboring TCs. Recently we have demonstrated that the 14-km-grid GCSRM can predict the timing of Typhoon 21st in 2006 with the lead time of more than 3 days, which was controlled by the westward propagating wave over the North Pacific. In 2008, Cyclone Nargis caused terrible disaster in Myanmar; we examined the predictability of Nargis genesis using the NICAM model.