A NUMERICAL INVESTIGATION OF SQUALL LINES .3. SENSITIVITY TO PRECIPITATION PROCESSES AND THE CORIOLIS-FORCE

The effects of various microphysical processes and the Coriolis force on the dynamics of squall systems were investigated with a two-dimensi onal, anelastic numerical model. The incorporation of ice-phase microp hysics into the model has been found to be important in the successful simulation of realistic storm structure and evolution of squall lines . The significance of the ice-phase microphysics is largely accounted for by the small terminal velocities of ice particles and cooling by m elting. The response of the atmosphere to the cooling by melting is a complicated one and has been shown to play an important role in shapin g the kinematic and precipitation characteristics of the observed and modeled squall systems. The interaction between the front-to-rear (FTR ) flow and cooling by melting would both intensify (by enhancing the m esoscale updraft and the FTR flow above the melting layer) and limit ( by partially driving the rear-to-front flow at the back of the stratif orm region) the stratiform precipitation development. The Coriolis for ce has also been found to have significant effects on the simulated sq uall systems. The rotational component of the storm flow field constra ins the strength of the divergent wind field, which in turn limits the horizontal scale of the mesoscale circulation and the associated stra tiform region. The model squall lines seemed to be most sensitive to t he variations of f in the range between f = 0.7 x 10(-4) s-1 and f = 1 X 10(-4) S-1.