NONHYDROSTATIC SIMULATIONS OF A COLD-FRONT OBSERVED DURING THE FRONTS-87 EXPERIMENT

A two-dimensional non-hydrostatic cloud model is used to simulate a fr ontal system observed on 11 November 1987 during the FRONTS 87 experim ent. The cloud-resolving model is able to reproduce a large variety of frontal bands, starting from only the meso-alpha-scale fields produce d by a hydrostatic forecast model. A narrow cold-frontal rainband is i dentified at the surface cold front. Two classes of wide bands are als o simulated: a wide cold-frontal rainband and warm-sector wide rainban ds. The vertical-velocity fields exhibit similar banded features in bo th the simulations and the Doppler-radar observations, with bands havi ng the same position, intensity and width. Several sensitivity experim ents are presented. One of them shows that the initial knowledge of th e ageostrophic circulation is not necessary to give a successful simul ation. Other experiments show that the along-front baroclinicity drive s the wide-band formation whereas the along-front deformation is not i mportant. The heat, moisture and horizontal momentum budgets are also investigated, in order to determine the rainband effects on larger sca les.