SIMULATION OF AN OBSERVED SQUALL LINE WITH A MESO-BETA-SCALE HYDROSTATIC MODEL

This paper reports on simulations of an observed squall line with the meso-beta-scale hydrostatic PERIDOT model. An attempt is made to answe r the question of what model changes are necessary to roughly simulate a squall line with a hydrostatic model lacking explicit microphysics. A qualitatively satisfactory simulation is obtained by modifying the physical package of the model and by increasing the resolution compare d to that of the operational model. Sensitivity experiments are conduc ted in order to determine the necessary components for the simulation of the squall line. The authors find that both increased resolution an d a downdraft parameterization are required. The energetics of the inn er circulation of the squall line are investigated using the best simu lation. The main supply for the rear to front now is identified as con version of potential energy into kinetic energy, which is linked to th e line-normal horizontal gradient of perturbation pressure. This resul t agrees with the conclusions of the sensitivity experiments and with previous studies on the important role played by the density current i n squall-line propagation.