Climate simulation for typhoongenesis by high resolution AGCM

Each year, about 30 typhoons develop on the Western North Pacific basin. Some of them approach to or make landfall onto Japan. One of our concerns is how the ongoing global climate change will influence behavior of tropical cyclones. For example, how will the frequency and intensity of typhoons be modified and how the track of storms altered? Numerical simulation studies have been conducted to obtain hint of answer to the above kind of questions. Ideally, spatial resolution of the models used should be sufficiently fine so that the simulated storms exhibit realistic scale and structure. A new supercomputer called Earth Simulator (ES) is a powerful tool to study various kinds of meso-scale phenomena. It is a vector-parallel computer composed of 640 nodes with each having 8 processors. It enables us to run the atmospheric general circulation model (AGCM) with horizontal resolution of a few tens kilometers. In other words, the model can be regarded as a global meso-scale model. It is considered appropriate to use such a model in investigation of impact of the global change on meso-system as well as on regional climate. The AGCM for ES (AFES) is constructed through inter- and inter-node parallelization and vectorization. The model is based on the AGCM version 5.4.02 of CCSR/NIES. In the present talk, we show the results from the AFES with T319L24, i.e., T319 horizontal resolution and 24 vertical layers. As the first step of simulation of typhoon response to climate change, it is appropriate to study climatological field producing typhoons during northern summer. Time integration of the model started from the condition corresponding to January 1, 1979, in the NCEP/NCAR reanalysis and ran for 5 years with the use of seasonally varying climatological SST. It is found that frequency and intensity of typhoons vary year to year even though seasonally cyclic SST does not vary. Global circulation in an active typhoon year will be composed against that in an inactive year.