A Numerical Investigation of Squall Lines. Part I: The Control Experiment

Abstract

A two-dimensional, anelastic, cloud-resolving numerical model was used to simulate squall systems. Large domain and fine grid resolutions were utilized so that both the convective and mesoscale components of squall lines could be handled adequately. Detailed cloud microphysics including the ice phase and the Coriolis force have been included in the basic model. Both the life cycle and storm structure of observed squall systems have been simulated successfully. Some details in the observed precipitation and kinematic characteristics of squall lines, such as the locations of front-to-rear jet core, the base of the stratiform cloud, the formation of a transition zone, and the organized mesoscale updraft, have been simulated by the model. The storm-generated meso-?-scale low pressure center located behind the convective updraft has been shown to be instrumental in the initiation and maintenance of the mesoscale circulation and the associated trailing stratiform region. Diagnostically, the horizontal pressure gradient forces associated with this low center drove the front-to-rear flow as well as the front portion of the rear-to-front flow. The front-to-rear flow destabilized the upper troposphere to the rear of the squall line, thus providing a suitable environment for the development of the mesoscale updraft and stratiform precipitation. The storm-relative rear-to-front flow possessed a double jet core structure that was found to be forced by different zones of horizontal pressure gradient force in the interior of the storm.