Stochastic modeling of contrail formation

Contrails and contrail cirrus are the largest contributors of aviation radiative forcing, yet the exact quantification of their global impact remains far more uncertain compared to other sources, such as direct CO2 emissions. This uncertainty involves all phases of contrail lifetime –from formation until dilution in the free atmosphere. It is known for example that aircraft induce persistent contrails when flying in ice-supersaturated regions by providing condensation nuclei (soot particles or liquid aerosols) onto which ice nucleates and accumulates. These processes are strongly non-linear and also depend on the atmospheric conditions and engine setup among other parameters. Since it is not possible to explore the effects of all these parameters using detailed modeling such as 3D large-eddy simulations, low or mid-fidelity modeling approaches have been used in the literature with mixed success. In an effort to assist industry and modelers with design tools and flight trajectories definition, we developed an efficient computational method based on Reynolds Average Navier Stokes (RANS) simulations coupled to a stochastic model that captures the essence of jet turbulent mixing and the microphysical processes occurring in the plume. The method is validated for pure mixing using existing database of jet flow experiments and simulations, and it is then applied to contrail formation by activating simple ice microphysical models.