Ground-based contrail observations: comparisons with flight telemetry and contrail model estimates

Abstract. Observations of contrail are vital for improving understanding of contrail formation and lifecycle, informing models, and assessing contrail mitigation strategies. Ground-based cameras offer a cost-effective means to observe the formation and evolution of young contrails and can be used to assess the accuracy of existing models. Here, we develop a methodology to track and analyse contrails from ground-based cameras, comparing these observations against simulations from the contrail cirrus prediction model (CoCiP) with actual flight trajectories. The ground-based contrail observations consist of 14 h of video footage recorded on five different days over Central London, capturing a total of 1,619 flight waypoints from 283 unique flights. Our results suggest that the best agreement between the observed and simulated contrail formation occurs at around 35,000–40,000 feet and at temperatures at least 10 K below the Schmidt-Appleman Criterion threshold temperature (T_SAC). Conversely, the largest discrepancies occurred when contrails are formed below 30,000 feet and at temperatures within 2.5 K of T_SAC. On average, the simulated contrail width is 17.5 % smaller than the observed geometric width. This discrepancy could be caused by the underestimation of sub-grid scale wind shear and turbulent mixing in the simulation, and model representation of the contrail cross-sectional shape. Overall, these findings demonstrate the capability of ground-based cameras to inform weather and contrail model development when combined with flight telemetry.