Abstract
Three numerical simulations of cyclogenesis in a baroclinic channel model with realistic physical parameterizations are compared to examine the influence of surface heat and moisture fluxes on the structure and development mechanisms of an idealized midlatitude cyclone. Identical atmospheric initial conditions are used in the three numerical simulations, which differ only in their surface flux conditions. The impact of the surface heat and moisture fluxes on the thermal structure and vertical circulation in the model cyclone is examined by comparing the geopotential height, temperature, static stability, surface convergence and wind stress as well as the surface heat and moisture flux distributions in the three simulations. Boundary layer stratification effects on convergence are examined and the associated changes in the boundary layer-free atmosphere interaction are compared.
Results indicate that the direct influence of the surface beat and moisture fluxes is limited to the boundary layer structure of the developing cyclone except when horizontal variations in the surface wind stress act to increase the boundary layer convergence. Upward surface heat fluxes to the northeast of the surface low and warm front produce unstable boundary layer stratification in this region, which increases the downward momentum fluxes and associated ageostrophic flow toward the surface low and warm front. Increased convergence results and increases the vertical circulation and the release of latent heat above the boundary layer due to this increased Ekman convergence. This boundary layer-free atmosphere interaction offsets the strong damping effect of the surface heating to lessen the baroclinity from which the cyclone derives its energy.
