Response of convection to relative sea surface temperature: Cloud-resolving simulations in two and three dimensions

Abstract

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 performed in both 2-D and 3-D geometries. The target profile toward which horizontal mean free tropospheric temperature is relaxed is held fixed, while sea surface temperature (SST) is varied. Consistent with previous studies, large-scale ascent and precipitation increase under WTG as the SST is increased, but more rapidly in two dimensions than in three dimensions. This is related to greater extremes of near-surface buoyancy in two dimensions as well as a lower gross moist stability, and perhaps also to weaker entrainment. In both two and three dimensions, 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. Copyright 2011 by the American Geophysical Union.