EXPLOSIVE MARINE CYCLOGENESIS IN A 3-LAYER MODEL WITH A REPRESENTATION OF SLANTWISE CONVECTION - A SENSITIVITY STUDY

A three-layer primitive equation model with a representation of slantw ise convection is used to study explosive marine cyclogenesis. A simpl e representation of boundary layer and shallow and deep cloud types is considered. Apart from the control simulation, experiments are conduc ted to test the sensitivity of the bent-back warm front and the explos ive deepening to various model parameters. The major results are as fo llows: 1) The control simulation produces a realistic explosive cyclon e. 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, ess entially determines the cloud mass flux transported into the large-sca le atmosphere. The thermal gradient in the bent-back warm frontal regi on and the final deepening strongly depend on this parameter. 3) Shall ow clouds are relatively insignificant in affecting the dynamics of ex plosive cyclones. 4) The surface drag force weakens the development of strong horizontal wind shear and the bent-back warm front. 5) The the rmal gradient in the bent-back warm front gradually increases with the thermodynamic disequilibrium between the sea surface and the atmosphe ric boundary layer. 6) Enhanced vertical wind shear increases the deep ening rate. However, the asymmetry in the wave development and strong pressure falls near the warm front are associated with slantwise conve ction. 7) Weak low-level stability has significant impact on cyclogene sis. 8) The effect of stable condensation is to moderately accelerate the development of the baroclinic wave.