Development of Kyushu University Atmosphere-Ocean General Circulation Model and Research of Climate

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The objective of this project is to develop the Kyushu University Atmosphere-Ocean general circulation model, and to investigate the short term climatic changes such as El nino and ENSO. The research of this project has been done by two different methods.At first, in order to understand the theoretical background of the coupled ocean-atmosphere dynamics, a simplified atmosphere-ocean coupled model is constructed by using Anderson-McCreary type ocean model and Gill type atmosphere model. Several numerical simulations have been done to investigate the necessary condition for generating the Elnino. It is found that the high oceanic heat content in the westem Pacific and the westerly burst over the western Pacific are the necessary condition for the generation of the El nino. Some numerical integrations have also been done to simulate the ENSO cycle. The model used in these integrations consists of a limited ocean surrounded by lands imitating the Pacific Ocean. An external land heating we … More st of the Pacific is added to simulate the land heating associated with the monsoon. The repetitious generation of the coupled disturbance has nothing to do with the linear model of Hirst (1988) as well as off-equatorial Rossby waves. It is perfectly determined by the amplitude of the external land heating. The mass budget analysis demonstrates that the change of zonal wind direction in the western Pacific, which is due to relative importance between the external land heating and the heating associated with the previous coupled disturbance, modulates the oceanic heat content relevant to the origin of the following coupled disturbance. This mechanism gives the oscillation between two stable equilibria (La Nina and El Nino), which are very different from those described in Battisti (1988), Schopf and Suarez (1987), and Zebiak and Cane (1987). Despite lots of model limitations, the present results seem to be compatible with the recent analyses of the air-sea-land system in the western Pacific.A numerical experiment has been performed using a coupled ocean-atmosphere model in order to examine possible relationships between the atmospheric intraseasonal oscillation and the air-sea coupled interannual disturbance. The model is composed of a T21 atmospheric general circulation model and a simple ocean model. When the ocean is kept motionless with a fixed SST, intraseasonal oscillation is reproduced in the atmosphere. When the ocean is replaced by the active one, the intraseasonal oscillation becomes rather sporadic both in space and time over the warm ocean region produced by the ocean-atmosphere interaction. The mean structure of this warm SST region is very similar to that obtained by the simple coupled ocean-atmosphere model. However, The coupled disturbance in this model has a multi-scale structure having both intraseasonal and interannual modes. Less