SST sensitivities in multiday TOGA COAREA cloud-resolving simulations

Abstract

A two-dimensional cloud-resolving model (CRM) was used to simulate the evolution of convection over the western Pacific between 19 and 26 December 1992, during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. A control simulation (CONTROL) was performed in which observed, time-evolving, spatially homogeneous SSTs were used as a lower boundary condition. It showed that the CRM was able to properly represent the evolution of the cloud systems. Sensitivity experiments were carried out, in which the sea surface temperature was increased (SST+) or decreased (SST-) by 1°C and the same evolving large-scale forcing used in CONTROL. The similarities among all simulations suggested that the large-scale forcing is the dominant mechanism controlling the statistics of the cloud systems, including the total precipitation. However, the convective-stratiform partition of the cloud systems was altered, the convective part being favored in SST+ and the stratiform part favored in SST-. In terms of the radiative budget, the reduced low-level cloud coverage in SST+ acted to compensate the enhancement of high-cloud coverage produced by more vigorous convection (the opposite occurred in SST-). As a consequence, the surface downward radiation was approximately the same in CONTROL, SST+, and SST-.