Explosive Marine Cyclogenesis in a Three-Layer Model with a Representation of Slantwise Convection: A Sensitivity Study

Abstract

A three-layer primitive equation model with a representation of slantwise convection is used to study explosive marine cyclogenesis. A simple representation of boundary layer and shallow and deep cloud types is considered. Apart from the control simulation. experiments are conducted to test the sensitivity of the bent-back warm front and the explosive deepening to various model parameters. The major results are as follows: 1) The control simulation produces a realistic explosive cyclone. 2) The cloud mass fraction at the top of the boundary layer, which is equal to the fractional area of slantwise ascent in a grid box, essentially determines the cloud mass flux transported into the large-scale atmosphere. The thermal gradient in the bent-back warm frontal region and the final deepening strongly depend on this parameter. 3) Shallow clouds are relatively insignificant in affecting the dynamics of explosive cyclones. 4) The surface drag force weakens the development of strong horizontal wind shear and the bent-back warm front. 5) The thermal gradient in the bent-back warm front gradually increases with the thermodynamic disequilibrium between the sea surface and the atmospheric boundary layer. 6) Enhanced vertical wind shear increases the deepening rate. However, the asymmetry in the wave development and strong pressure falls near the warm front are associated with slantwise convection. 7) Weak low-level stability has significant impact on cyclogenesis. 8) The effect of stable condensation is to moderately accelerate the development of the baroclinic wave.