A GCSS model intercomparison for a tropical squall line observed during TOGA-COARE. I: Cloud-resolving models

Results from eight cloud-resolving models are compared for the first time f or the case of an oceanic tropicalsquall line observed during the Tropical Ocean/Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. There is broad agreement between all the models in describing the overall struct ure and propagation of the squall line and some quantitative agreement in t he evolution of rainfall. There is also a more qualitative agreement betwee n the models in describing the vertical structure of the apparent heat and moisture sources. The three-dimensional (3D) experiments with an active ice phase and open la teral boundary conditions along the direction of the system propagation sho w good agreement for all parameters. The comparison of 3D simulated fields with those obtained from two different analyses of airborne Doppler radar d ata indicates that the 3D models are able to simulate the dynamical structu re of the squall line, including the observed double-peaked updraughts. How ever, the second updraught peak at around 10 km in height is obtained only when the ice phase is represented. The 2D simulations with an ice-phase par ametrization also exhibit this structure, although with a larger temporal v ariability. In the 3D simulations, the evolution of the mean wind profile is in the sen se of decreasing the shear, but the 2D simulations are unable to reproduce this behaviour.