Response of convection to relative SST: Cloud-resolving simulations in 2D and 3D

The properties of equilibrated tropical convection are studied using a cloud-resolving model with large-scale dynamics parameterized by the weak temperature gradient (WTG) approximation. Model integrations are carried out in both two-dimensional (2D) and three-dimensional (3D) geometries. The target profile towards which horizontal mean free tropospheric temperature is relaxed is held fixed while SST is varied. Consistent with previous studies, large-scale ascent and precipitation increase under WTG as the SST is increased, but more rapidly in 2D than 3D. This is related to greater extremes of near-surface buoyancy in 2D as well as a lower gross moist stability, and perhaps also to weaker entrainment. In both 2D and 3D, the vertical profiles of large-scale vertical velocity are top-heavy and remarkably self-similar in shape as SST is increased. When all integrations are analyzed together, precipitation increases with column-integrated relative humidity once the latter reaches a threshold, as in observations and other models. However, within each integration, the two quantities are correlated negatively, albeit over a very narrow range.