Improving forecasts of persistent contrails through ice deposition adjustments

Abstract. Aviation-induced clouds, especially persistent contrails, contribute significantly to anthropogenic climate forcing, often surpassing the short-term impact of aviation CO2 emissions. These clouds form in ice-supersaturated regions, where they trap longwave radiation and warm the climate. On 25 November 2023, widespread ice-supersaturated layers over eastern Canada and the USA led to extensive contrail formation, confirmed by GOES-16 satellite imagery and ground-based photography. Atmospheric conditions were characterized using ceilometer data from Toronto Pearson Airport and radiosonde soundings. To investigate these events, high-resolution, limited-area simulations were performed using the Global Environmental Multiscale (GEM) model coupled with the Predicted Particle Properties (P3) microphysics scheme. A deposition-adjusted simulation incorporating the deposition coefficient reduced ice particle growth rates and enhanced upper-tropospheric moisture buildup, shifting the relative humidity with respect to ice peak from ∼102 % to ∼108 %, closer to observations. The Contrail Avoidance Tool, a diagnostic for identifying and forming persistent contrails, was then applied to simulate persistent contrails for an A321 and a B747 under varying soot emission regimes. The B747 maintained higher contrail ice number concentrations (CINC) because its higher fuel flow injected more soot per flight distance, partly offset by wake-vortex sublimation. Consequently, a low-soot B747 produced CINC comparable to an A321 burning conventional Jet A fuel. Aircraft-specific wake dynamics and soot regimes jointly control ice crystal survival, indicating that contrail models using constant soot emission indices without accounting for wake-vortex losses may overestimate contrail ice production and possibly contrail radiative impacts.