A numerical experiment in predicting stratus clouds

Abstract

This study is concerned with the development and testing of a theoretical model for predicting the formation of air-mass stratus clouds in the region of south-central Texas. The basic equations which define the model are the horizontal equations of motion, the continuity equation for incompressible flow, the first law of thermodynamics for non-adiabatic processes, and the equation which expresses the conservation of mass for water substance. The vertical variation of pressure is assumed to be hydrostatic. Free -air temperature changes due to the divergence of radiative flux are disallowed. The turbulent transfer of heat, moisture, and momentum is permitted. Precipitation is excluded. The equations are integrated numerically with respect to time over a two-dimensional grid which has one axis oriented perpendicular to a coastline and the other axis oriented vertically. The grid is arrayed approximately along a line through Beeville, Texas and San Antonio, Texas with one boundary 20 km offshore and the other boundary 280 km inland. The vertical extent of the model is approximately 1 km. All variables except pressure are assumed to be horizontally homogeneous in a direction parallel to the coast. The initial conditions are chose so that they depict as closely as possible the conditions existing in the region of south-central Texas in the late afternoon of a specific day on which stratus formed later in the evening. ...