Hadley circulations and large-scale motions of moist convection in the two-dimensional numerical model

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 Delta T-s are investigated. The numerical results show that a systematic multi-cell structure exists in every experiment. If the surface temperature is constant (Delta T-s = 0), convective motions are organized on the scale of the Rossby deformation radius and their precipitation patterns have a periodicity of the advective time tau(D). As Delta T-s becomes larger, the organized convective system tends to propagate toward warmer regions. The convective cells calculated in the Cartesian coordinate model are very similar to those of the mid-latitudes in the spherical coordinate model. As the convective cells approach the equator, their cell scales become larger. In particular, in the case of the symmetric condition about the equator, the Hadley cell can be regarded as one of the convective cells which exists at the equator.