Three-Dimensional Modeling Study of Squall Lines Observed in COPT81

Abstract

Two long-lived tropical squall lines (TSLs) observed during the COPT81 experiment are studied numerically by using a three-dimensional compressible model with warm-rain cloud physics. An initial impulse of potential temperature and moisture, which is made from the retrieved data of Doppler radar, is adopted to initiate the TSL efficiently. To examine cell structures in the convective region, a large-domain model (normal-to-TSL domain length Lx ? 2300 km) with no forcing is used. Quasi-equilibrium three-dimensional convective systems, in which cells evolve repetitively, are simulated in both TSLs. In the strong convective TSL case, transient short-lived cells characterized by intense updrafts and active development of new cells at the leading edge are attained. The convective region is composed of several cells with different evolution stages, and is multicellular. In the weak convective TSL case, long-lived cells and slow development of new cells are simulated. These features are compared with observations and other numerical results. Four sensitivity experiments are performed to examine (i) a role of the parallel-to-TSL basic wind, (ii) comparison between two- and three-dimensional simulations, (iii) the impact of Lx on quasi-equilibrium characteristics of the convective system, and (iv) the effect of the rear-inflow forcing.