Implementation of a non-hydrostatic, adaptive-grid dynamics core in CAM3. Part II: dynamical influences on ITCZ behavior and tropical precipitation

Previous aqua-planet simulations reported in the literature have shown the existence of both single and double inter-tropical convergence zones (ITCZs). In this study, horizontal grid resolution strongly affects ITCZ morphology as well as the amount of tropical precipitation through its influence on resolved dynamics. The grid adaptation capability of our global model enables simulations that separate the influence of tropical and extra-tropical dynamics on both the ITCZ and tropical precipitation. The presence of single versus double ITCZs in our aqua-planet simulations depends on the resolution of convectively coupled equatorial waves. When the tropical resolution is sufficiently high to resolve prominent equatorial waves a double ITCZ occurs, otherwise a single ITCZ occurs. In contrast, tropical resolution does not affect the magnitude of tropical precipitation in our aqua-planet simulations. Instead the magnitude is sensitive to extra-tropical resolution, through its influence on the strength of baroclinic eddies and their forcing of the Hadley circulation.