Simulation of the hierarchy structure in tropical disturbances by a three-dimensional model treating the cloud physical process

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Tropical disturbances generally have the hierarchy structure. The typical example is the intraseasonal oscillation in which superclusters having the scale of 1, 000km are composed of mesoscale convection having the scale of lOOkm. The aim of this research is to simulate this hierarchy structure of tropical disturbances, using a model with Yamasaki's parameterization. In this parameterization, cloud water and rainwater as well as water vapor are predicted, and meso-scale convection can be resolved explicitly. The grid length is as fine as 40km in the tropics. Therefore, we can perform a qualitatively different experiment from previous ones. The surface is covered with the ocean whose temperature is zonally uniform and symmetric with respect to the equator.In the simulation, convection near the equator is suppressed and the supercluster does not appear ; the hierarchy structure associated with the intraseasonal oscillation is not well simulated. However, the ITCZ is formed along about 10ﾟN and 10ﾟS, and ITCZ disturbances show the hierarchy structure. That is, their scales are 1, 000km or more, and are composed of meso-scale convection with the scale of 100km. The disturbances generally move westward, while the meso-scale convection is almost stationary. Also in this respect, the characteristics of the hierarchy structure are simulated. Further, it is suggested that these results are attributed to several inherent effects of this model.In the future, sensitivity experiments must be carried out. In particular, an experiment for radiative cooling is important, because this affects the static stability, which in turn has a great influence on the activity of convection near the equator and the moving direction of disturbances. The hierarchy structure associated with the intraseasonal oscillation will probablyappear in this course.