Three-dimensional simulation of cloud street development during a cold air outbreak

Abstract

A three-dimensional numerical model is used to study boundary-layer eddy structure during a cold air outbreak. The model explicitly represents the large-scale three-dimensional motions, while small-scale turbulence is parameterized; it contains a water cycle with cloud formation and it takes into account infrared radiative cooling in cloudy conditions and the influence of large-scale vertical motions. The model is applied to conditions corresponding to an observed case of cloud street/stratocumulus development which occurred over the Greenland Sea during the ARKTIS 1988 experiment. The boundary layer is found to grow rapidly as the cold air flows off the ice over the relatively warm water. Coherent structures were identified in this boundary layer. It is found that the rolls become increasingly more convective in character with distance from the ice edge. Qualitative and quantitative descriptions of the flow field are given. Additionally, the relative importance of the various physical processes and external parameters in the evolution of the mean field of variables is indicated.