Development of a general circulation model of the middle atmosphere

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In this project we have developed a community general circulation model of the middle atmosphere. This model is based on the community general circulation climate model for troposphere and lower stratosphere developed by A. Sumi at University of Tokyo, this model was originally developed by kanamitu et. al. at Japan Meteorological Agency.The model developed in this project is a spectral model with T21 horizontal resolution, which includes from the ground to 83km height(Model 1) and from the ground to 160km height(Model 2). As a vertical coordinate system, a sigma phybrid coordinate is used with a resolution of about 2.5km. Newtonian cooling radiation scheme is used in the stratosphere, mesosphere and lower thermosphere. In the near future a more accurate radiation scheme will be introduced.A trial integration was conducted for two Model years using model 1. It is shown that the model has a capability to represent a qualitative structure of the middle atmosphere circulation. A stratospheric sudden warming like events are also simulated in the models northern hemisphere winter.A diurnal cycle of the radiation is included in the model. In Model 2, the upper boundary is high enough to simulate the vertical propagation of the tidal waves. A trial integration using Model 2 shows that the tidal waves are breaking at about 100km height and easterlies are induced by the momentum deposition due to the breaking.This model is also used as an nonlinear integrator. As an example, a non-linear propagation of the diurnal tidal waves is investigated. It is shown that the dry convective adjustment and the nonlinearity in the model can simulate the saturation of the wave at about 100km height.