Radiative Effect of Two Contrail Cirrus Outbreaks Over Western Europe Estimated Using Geostationary Satellite Observations and Radiative Transfer Calculations

Estimation of the perturbation to the Earth's energy budget by contrail outbreaks is required for estimating the climate impact of aviation and verifying the climate benefits of proposed contrail avoidance strategies such as aircraft rerouting. Here we identified two successive large-scale contrail outbreaks developing in clear-sky conditions in geostationary and polar-orbiting satellite infrared images of Western Europe lasting from 22-23 June 2020. Their hourly cloud radiative effect, obtained using geostationary satellite cloud retrievals and radiative transfer calculations, is negative or weakly positive during daytime and positive during nighttime. The cumulative energy forcing of the two outbreaks is 7 PJ and -8.5 PJ, with uncertainties of 3 PJ, stemming each from approximately 15-20 flights over periods of 19 and 7 hr, respectively. This study suggests that an automated quantification of contrail outbreak radiative effect is possible, at least for contrails forming in clear sky conditions. Contrail cirrus is produced by aircraft and perturb the energy budget of the Earth. However, the actual size of the perturbation is uncertain. In this study, we calculate the energy budget perturbation of two successive contrail-cirrus outbreaks over Western Europe from 22-23 June 2020. An infrared image composite allows the identification and tracking of contrails with a 15 min frequency, which is verified by comparison to satellite images with better horizontal resolution from several polar-orbiting platforms. Cloud properties of the contrail-cirrus clusters, estimated from geostationary satellite data, are used in radiative transfer calculations. We find that one contrail cirrus outbreak adds an average power of 2 TW over 20 hr, while the other removes 3.3 TW over 8 hr. This cumulative energy depends on the lifespan and cloud properties of the outbreaks. This case study suggests that geostationary satellite observations allow the estimation of the energy perturbation of a contrail outbreak, with encouraging implications for contrail-cirrus monitoring and the verification of contrail avoidance strategies. The cloud radiative effect (CRE) of two successive contrail-cirrus outbreaks is estimated from geostationary satellite measurements These two outbreaks have different CRE sign and magnitude, which can be explained by their different cloud properties and time evolutions The study suggests that automated quantification of contrail-cirrus CRE for monitoring or verification of contrail avoidance is feasible