A comparison of convergence- and surface-flux-based convective parameterizations with applications to tropical cyclogenesis

The evolutions of radially symmetric vortices and idealized easterly waves are compared using three simple convective parameterization schemes. The pa rameterizations are formulated for a model atmosphere consisting of three c oupled, shallow, constant-density layers. The first was developed by Ooyama and later refined by DeMaria and Pickle (the ODP scheme). Their scheme use s horizontal convergence in the boundary layer to define a vertical mass fl ux, along with a closure relation based on conservation of moist static ene rgy that determines the vertical redistribution of mass. The second scheme is a modification of the ODP scheme in that convection is allowed to stabil ize the profile. A third scheme has the convective mass flux from the bound ary layer determined by the assumption that convective up- and downdrafts k eep the equivalent potential temperature of the boundary layer in near equi librium (the BLQ scheme). For vortices that are initially radially symmetric, the ODP scheme produces a hurricane-like vortex, provided that the middle atmosphere is sufficient ly moist. However, the intensification is slow unless an unrealistically we ak density stratification is used. For the modified ODP scheme, the vortex intensifies on a shorter timescale in an atmosphere with a realistic strati fication, regardless of the midlevel moisture profile. After the intensific ation, convective transport of air with high equivalent potential temperatu re stabilizes the profile, and the vortex begins to decay. For the BLQ sche me, the vortex will intensify, provided that the middle atmosphere is suffi ciently moist and after the atmosphere has been conditioned for deep convec tion by the shallow convection. For the idealized easterly waves, the development between the schemes is qu ite different. Only the BLQ scheme allows convection to condition the atmos phere for further deep convection, which results in a developing disturbanc e.