Numerical Modeling of Precipitation Cores on Cold Fronts

Abstract

A nonhydrostatic, three-dimensional, mesoscale model, including cloud physics, is used to simulate the structure of a narrow cold-frontal rainband (NCFR). The model simulations reproduce the observed ?core?gap? structure of the NCFR. Trapped gravity waves, triggered by regions of stronger convection on the cold front, induce subsidence and regions of warming aloft. In these regions, precipitation is suppressed, thereby creating precipitation gaps along the front separated by precipitation cores. The advection of hydrometeors is responsible for the parallel orientation and the elliptical shapes of the precipitation cores. Gravity waves produce pressure perturbations just behind the cold front, which modify the wind and thermal structure. Parts of the front behave locally like a gravity current, traveling at the theoretical gravity current speed in a direction perpendicular to the local orientation of the front, but the motion of the front as a whole is not well described by the gravity current speed calculated from quantities averaged along the length of the front.