Rapid simulation of 2-D contrail cross sections through Contrail Layer Approximation using Multi-crystal Particles (CLAMP) v1.0

Abstract. Aircraft condensation trails (contrails) are increasingly studied with the aim of understanding and mitigating their climate impacts. Forming at the scale of a single aircraft, an individual contrail can take several hours to become large enough to be resolved by global-scale climate models, if they are resolved at all. High-fidelity simulations of individual contrails are too computationally intensive for use in global applications, but comparisons with existing reduced-order parameterizations have shown the need for approaches which can capture the development of size-resolved structures in the contrail as well as the dynamic interaction of contrail ice with the ambient humidity field. We introduce a new model of contrail physics, the Contrail Layer Approximation using Multi-crystal Particles (CLAMP) v1.0. CLAMP resolves challenges observed in other reduced-order models including lack of thermodynamic consistency and the inability to represent heterogeneity between the primary and secondary wakes due to gravitational sorting, providing an intermediate-fidelity simulation of a contrail with typical run times of about 60 seconds on one computational core for a 12-hour case. We use CLAMP to simulate the physics and radiative forcing of contrails across a broad parameter space, evaluating the effect of synoptic-scale downdrafts, mixing, settling, and gravity waves on contrail lifetime and climate impacts. We find that gravity wave forcing in particular may shorten contrail lifetimes, but that the stochastic nature of these effects is unlikely to be well captured by simple parameterizations. We also compare CLAMP to published results from other, more computationally expensive models, finding that it reproduces key trends in contrail properties with respect to common meteorological and aircraft parameters at a fraction of the computational cost. Furthermore, we show that carefully enforcing closed mass and energy budgets – not currently the case for most Lagrangian contrail models - can drive large differences in contrail properties, implying a potential shortcoming of current-generation contrail simulations. Although more work is needed to evaluate models against observations of real-world contrail behavior, including determining the importance of such inconsistencies, CLAMP is proposed as an alternative to existing single-contrail models for standalone contrail studies with sufficient speed and flexibility to inform emulations for use in global climate modeling applications.