The potential for thin clouds to enhance the greenhouse effect has led to considerable interest regarding the perturbation on cirrus cloud caused by the wake of commercial aircraft. It has been estimated that an increased cirrus cloud cover in the main global aircraft corridors of 2 to 10 percent yields significant effects on land-surface temperatures due to the absorption and scattering of solar radiation by the thin cloud. Cloud-ice is formed via homogeneous freezing nucleation of ambient haze droplets in the upwelling limbs of the wake vortex pair behind an aircraft. The aerodynamically induced ice clouds are similar in microphysical and radiative respects to contrails as formed by the nucleation of exhaust particles. Numerical simulation has been conducted to study the evolution of the aerodynamically induced thin clouds, which depends on the dynamic properties of the wake and the ambient atmosphere. Turbulence also plays an important role in the slow dissipation process. The commonly used formulation relating stress tensor and grid-scale strain rate tensor is inadequate for this study. A generalized formulation that relates stress tensor to strain rate tensor and vorticity is used. The coefficients are self-determined by using a dynamic closure method. This method converts previously prescribed subgrid-scale (SGS) model coefficients for turbulent flow to nonsingular and self-determined parameters that vary with space and time. Within the large eddy simulation (LES), the SGS representation is locally and dynamically adjusted to match the statistical structure of the smallest resolvable eddies.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics