Persistent Contrails and Contrail Cirrus. Part II: Full Lifetime Behavior

Abstract

ore than 200 large-eddy simulations of long-lived contrails from several-seconds age until their demise have been performed and their lifetime-integrated behavior has been analyzed. The simulations employ size-resolved microphysics and include variations of effective ice crystal number emission index, temperature, relative humidity with respect to ice, stratification, shear, supersaturated-layer depth, uplift/subsidence, and coupled radiation. Basic scaling behaviors are analyzed for contrail lifetime, width, ice mass, and surface area. Lifetimes exceeding 40 h, widths exceeding 100 km, and ice masses exceeding 50 kg m?1 of flight path were sometimes encountered. Distinct behavior regimes produced by radiative forcing are identified and found to be predicted by a simplified model. The lifetime-integrated ice crystal surface area per length of flight path SΣ is used as an approximate metric of contrail significance, and a simple, physically based model is derived. Over much of the parameter space, SΣ is found to vary approximately simply as the product of the maximum contrail depth and the effective number of ice crystals per flight path; other parameters have their impact on SΣ dominantly through their effects on these two quantities. Model and simulation results highlight the importance of crystal number loss mechanisms, the interaction between shear and ice sedimentation, the depth of the supersaturated layer below flight level, and the potential integrated significance of ?cold? subvisible contrails. The results can aid in estimating the effects of more complex contrail scenarios or mitigation strategies and in understanding some aspects of natural-cirrus dynamics.