Constraints on Tropical Convection and Precipitation in a Changing Climate

During the last 100 years, except for a cessation in the late 1940s to early 1970s, there has been a steady increase in the temperature of the planet. The SST in all oceans has increased with the largest change occurring in the tropical Indian Ocean. Yet, whilst the overall SST has increased, the area of active and precipitating convection in the tropics has remained the same. But within this relatively constant area of convection, the intensity of convection appears to have marginally increased. These observations suggest that a critical SST value does not exist for convection to occur. Other constraints must determine convection.

In addition, during this period of warming, a number of curiosities have emerged: The ratio between the total annual precipitation of the northern and southern hemispheres (measured either in terms of rate or volume) has remained the same despite the large differences in the geography of the two hemispheres and the unevenness of SST changes. Also, annual averaged top-of-the–atmosphere radiation between the two hemispheres has remained essentially identical. Finally, while there has been a constancy in the area of positive column integrated heating, and etc., there appears to be an oscillation between total heating over land and ocean areas. Here, we explore the basic thermodynamic/dynamic constraints that produce interhemispheric symmetry and synergies in the present climate and what these constraints may portend for the future climate. This paper is presented in honor of the substantial and fundamental contributions to the understanding of the dynamic and thermodynamics of the tropics by Professor Wayne Schubert throughout his distinguished career.