Modeling Aircraft Contrails and Emission Plumes for Climate Impacts
Stanford University, 2011
Aircraft emissions lead to contrails and change cloud coverage in the upper troposphere/lower stratosphere, but their quantitative impact on climate is highly uncertain. As environmental policy turns toward regulating anthropogenic climate change components, it will be necessary to improve quantification of the climate impacts of aviation. Toward this end, we present two models of aircraft emissions. The first model is a large eddy simulation (LES) with three-dimensional, eddy-resolving flow physics and ice deposition/sublimation microphysics. Modeled ice properties, cloud optical depths, and contrail width growth rates are consistent with observational field studies. A series of sensitivity cases shows the effect of various parameters over twenty minutes of simulation time. The analysis focuses on properties such as contrail optical depth and cross-sectional width that are relevant to climate impacts. Vertical wind shear is found to have the strongest effect on these properties through the kinematic spreading of the contrail. In cases with no shear, optical depth is most sensitive to aircraft type and ambient humidity. One model parameter, the effective emission index of ice crystals, is also found to affect optical depth. A subset of the LES cases is run for two hours of simulation time to approach the scale of dynamical time steps modeled by global climate simulations. These cases use more realistic ice microphysics, including sedimentation, and forced ambient turbulence, both of which are processes that control contrail development at late times. The second model is a simple, low cost parameterization of aircraft plume dynamics, intended to be used as a subgrid plume model (SPM) within large scale atmospheric simulations. The SPM provides basic plume cross-section time advancement that has been used as a dilution model within a coupled global atmosphere-ocean climate simulation to study the effects of aviation on air quality and climate. Comparison to the twenty-minute and two-hour LES results demonstrates that the SPM captures important plume development characteristics under the effect of vertical shear and atmospheric turbulence.
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aircraft type ambient air atmospheric baseline contours of exhaust contours of ice contrail simulations contrail width CP/b cross-section dispersion phase Domain integrated Dürbeck and Gerz emission index equations exhaust scalar Figure flight Flight-direction averaged contours fluid dynamics Gaussian Gerz global climate model horizontal humidity with respect ice area ice mass density initial condition isosurface Konopka Lagrangian large eddy simulation Lewellen Medium 2-Engine Ncomp optical depth optical properties parameters particle number density particle statistics PDFs plotted against simulation primary wake relative humidity respect to ice row shows spanwise row shows streamwise row shows vertically second row shows sedimentation sensitivity Shirgaonkar and Lele shows spanwise integrated shows streamwise averaged shows vertically integrated simulation domain spanwise integrated contours streamwise averaged contours supersaturated temperature third row shows throughout the simulation turbulence twenty-minute simulations two-hour simulations vertical shear vertically integrated contours vortex phase vortex system vortices water vapor wavenumber wind shear