| Popis: |
Numerical experiments are conducted with a hydrostatic primitive equation model initialized in a baroclinically unstable state to simulate the passage of cold fronts over the ocean. The model includes K-theory planetary boundary layer (PBL) parameterization with implicitly defined diffusion coefficients. An adiabatic and inviscid simulation provided the control for these experiments. The PBL simulations are integrated 1) with zi held constant at 0.4 m and no heat flux; 2) with sea surface temperature (SST) set equal to e1 at t = 0 h; 3) with a 5 warmer SST; 4) with diffusion coefficients set equal to 1. Horizontal resolution is increased to achieve smaller scale fronts in the inviscid and ocean simulations. The frontogenetic effects of shear, tilting, convergence, and the PBL on isentropic surfaces are evaluated. Relative to the inviscid simulation, the PBL simulations produce reduced frontogenesis. Surface heat and momentum fluxes combined with turbulent mixing of heat promote the development of a deep, well-mixed layer whose depth is dependent on the air-sea temperature difference. The rate of frontogenesis is extremely dependent on the parameterization of the PBL, specifically surface roughness lengths. Smaller scale fronts were produced during the ocean simulations than the PBL land case. Forcing in all simulations is due primarily to shearing deformation initially. As the wave grows in amplitude, convergence contributes more to frontogenesis than shear. Other terms in the frontogenetic equation become important in the PBL simulations. |
