S ep 1 99 5 Hadley circulations and large scale motions of moist convection in the two dimensional numerical model Masaki Satoh

As a tool for understanding the meridional circulation of the atmosphere, a two-dimensional ( latitude – height ) numerical model is used to clarify the relationship between the Hadley circulation and large-scale motions associated with moist convection. The model is based on the primitive equations including the moist process, and two kinds of coordinates are used: the spherical coordinate and the Cartesian coordinate with a uniform rotation. The surface temperature is externally fixed and the troposphere is cooled by the radiation; unstable stratification generates large-scale convective motions. Dependencies on the surface temperature difference from north to south ∆Ts are investigated. The numerical results show that a systematic multi-cell structure exists in every experiment. If the surface temperature is constant (∆Ts = 0 ), convective motions are organized in the scale of the Rossby deformation radius and their precipitation patterns have a periodicity of the advective time τD. As ∆Ts becomes larger, the organized convective system tends to propagate toward warmer regions. The convective cells calculated in the Cartesian coordinate model is very similar to those of the mid-latitudes in the spherical coordinate model. In particular, the Hadley cell can be regarded as the limit of the convective cells in the equatorial latitudes.