The Linear Response of a Global Atmosphere to Mobile Heating

Abstract

The horizontal structures of circulations induced by mobile global heating are investigated by using the linearized shallow water equations on the sphere. The parameters involved in this system are the Lamb parameter (i. e., the parameter representing the effect of planetary rotation), the velocity of heat source and the damping rate (the coefficient of Rayleigh friction and Newtonian cooling). Numerical solutions for a wide range of these parameters are obtained by using the eigenmodes of shallow water equations (Hough functions). The circulations obtained are classified into the following four types. Type I is a direct circulation between the day and night sides. This type appears when the motion of heat source is slow and the damping rate is large. Type II is a “Gill pattern"-like circulation ; its horizontal flow pattern is similar to the “Gill pattern" obtained by Gill (1980), but it extends to the extratropics. This type appears when both the motion of heat source and the damping rate are small. Type III is a zonally uniform circulation. This type appears when the motion of the heat source is considerable. Type IV is a circulation characterized by an inertio-gravity wave. This type appears when the resonance of an inertio-gravity wave with mobile heating occurs. This resonance is conspicuous when the damping rate is small. In the regime diagram (in the parameter space), the region of Type IV exists between those of Types II and III.