How well can persistent contrails be predicted?

Abstract

To allow the planning of flights that avoid the formation of strongly warming contrails (so called Big Hits) it is necessary that three things can reliably be predicted from weather forecast data: 1) the formation conditions of contrails (Schmidt-Appleman criterion), 2) the persistence (ice-supersaturation or not) and 3) the expected instantaneous radiative forcing (iRF). In this paper we compare in-situ meteorological data from IAGOS/MOZAIC with and modelling data from meteorological reanalysis ERA 5 and chemistry-climate model EMAC (issues 1 and 2) and use radiation quantities from these models to estimate the iRF. We do this for all seasons. It turns out that contrail formation itself can be robustly predicted by using reanalysis data. The prediction of persistence is also quite reliable but less robust than the prediction of contrail formation. The estimate of optical thickness is of course not better than the estimate of the degree of supersaturation and thus the estimates of longwave, shortwave and net iRF differ substantially. It is clear that the problems originate mainly from the different relative humidities in the two data sources, and there are errors on both the modelling and the measurement sides. Our analysis of these errors and resulting differences can bring us further to the goal of green-flight planning, as atmospheric parameters are key for both assessing and avoiding aviation’s climate impact from contrail formation.