Global Cloud Resolving Simulations By NICAM

Frontier Research Center for Global Change ( FRCGC ) has been developing a new high-resolution global atmospheric model in cooperation with Center of Climate System Research ( CCSR ) in the University of Tokyo. This global model, called NICAM ( Nonhydrostatic ICosahedral Atmospheric Model ), is intended to be run in super high-resolution for the climate research. The main aim of the high-resolution simulation is to resolve the cumulus convection explicitly on the entire globe in order to eliminate the ambiguity of cumulus parameterizations. Therefore, our target resolutions are five km or less in the horizontal directions and several hundred m in the vertical direction. For such very high resolution simulations, we apply the icosahedral grid in the horizontal grid configuration. The idea of using the icosahedral grid goes back to the 1969 ( Williamson, Sadourny ). However, at that time, the icosahedral grid model was suffered from the wavenumber 5 problem owing to shape of original icosahedron and grid noise and so on. Recently, several research groups have been reconsidering the icosahedral grid. We have also employed a new icosahedral grid, which is modified by spring dynamics, and confirmed its availability as the horizontal grid for the global model. On the other hand, we have been developing a new nonhydrostatic scheme that is suitable to climate simulations ( long time integrations ). Since this scheme is based on the finite volume method, the model guarantees the conservation of mass. Further, by considering the conversion term between the energies, the new scheme also guarantees the conservation of total energy. In this talk, we introduce the numerical algorithm of NICAM and show the recent several results from the global cloud resolving run; aqua planet experiment, short term integration like as numerical weather prediction, perpetual July experiment for investigation of cloud feedback, and so on.