Abstract
Numerical simulations of two-dimensional tropical squall-line clusters (TSL) are performed using a nonhydrostatic, inelastic cloud model in the ambient winds and stratification, which are based on the sounding in GATE on Sept. 12, 1974. Water substance in the model is divided into 6 forms; water vapor, cloud water, rain, cloud ice, graupel and hail. The parameterization of cloud microphysics is mainly based on Lin et al. (1983). The grid sizes are stretched in both horizontal and vertical directions and the model domain is 241km and 14.45km in the horizontal and vertical direction, respectively. A cumulonimbus is initiated by an initial thermal under an imposed low-level large-scale convergence.
Quasi-steady convection is attained after 2 hours of the model integration. The convective system is composed of convective and stratiform regions. In the convective region, a slant strong updraft is obtained and its angle from the horizontal is about 15 degrees. In the stratiform region, motions are nearly uniform in the horizontal direction and layer structures of strong horizontal winds are seen. There is weak updraft in the anvil cloud which is occupied by graupel and weak downdraft below the melting level where rain prevails. The sharp jumps of winds, temperature, water vapor mixing ratio and heat/moisture fluxes are obtained near the gust front on the surface. These features of the convective system simulated in the model are similar to those of the observed TSLs. However, fast propagation of the convective system is not well simulated. This may be due to that the simulated pressure rise on the surface is not sufficiently large to proceed the convective system fast.
