The construction and application of numerical models to the study of cloud dynamics and the structure of winter frontal rainbands

Abstract

The objectives of the present research are to construct a set of equations for simulating the evolution of frontal systems, to develop a finite-difference scheme of their solution, and to carry out numerical modelling. Numerical models with detailed descriptions of cloud particle evolution (nuclei, drops, crystals, aggregates, etc.) including condensation (sublimation) and coagulation processes are constructed to study the inner structure of frontal mixed stratiform clouds and precipitation development. Two- and three-dimensional diagnostic and prognostic simulations of two occluded winter frontal systems that passed over Ukraine and a two-dimensional prognostic model of an occluded frontal system that passed over USA are presented. A two-dimensional model with nested and stretched grids is used for the simulation of convective cells embedded in stratiform. The structure of the simulated atmospheric fronts in occluded cyclones exhibits many common features described in other previous studies, for other mid-latitude regions: hyperbaroclinic zones of different scales within the mesoscale range, small and large mesoscale rainbands, embedded convective cells, wave-like features of cloud and precipitation evolution, etc. The qualitative estimations of instability in frontal zones implies that large rainbands can apparently be generated in baroclinic zones with stable stratification. In unstable zones, small mesoscale rainbands with embedded convective cells are mainly formed. The clouds' precipitation is determined largely by dynamical features. The mechanisms of ice nucleation, sublimation, freezing or coagulation processes have a crucial role in cloud and precipitation formation if there is an inability to realise all of the precipitable moisture.