Observing formation and early evolution of contrails formed by IAGOS aircraft using high-resolution LEO satellite imagery

Abstract. Persistent contrails and contrail cirrus are estimated to be a major contributor to the climate impact of aviation. The mitigation of these impacts by means of technological or operational changes benefits from the ability to skillfully model the formation, evolution, and impacts of contrails. Although these models can be evaluated and improved by use of observations of contrails obtained from remote sensing instruments, these comparisons are hindered by uncertainty in the required meteorological data (such as relative humidity) and limitations in the method of observation (such as younger contrails not being observable in geostationary satellite imagery). To address these challenges, we collocate aircraft equipped with in-situ humidity sensors from the IAGOS fleet in high-resolution (10–30 m) satellite imagery obtained by instruments aboard the low Earth orbit Sentinel-2 and Landsat missions. The resulting dataset consists of 543 IAGOS aircraft found in satellite imagery (51 % of which form contrails), which we use to evaluate predictions of contrail formation by the Schmidt-Appleman criterion (SAC) as well as predictions of contrail growth by the CoCiP model. When accounting for uncertainty in the IAGOS measurements of humidity and temperature, we find that the SAC correctly explains 98.3 % of the observations. Disagreement between predictions and observation increases when using meteorological data from the ERA5 reanalysis, with only 92.1 % of the observations being explained correctly. Out of the 195 annotated contrails, 48.2 % of these contrails were found to persist for longer than 10 s (approximately the jet phase) and 8.7 % longer than 120 s (approximately the vortex phase). The relative humidity with respect to ice is found to correlate most strongly with observed contrail lifetime, exhibiting an R² value of 0.49 with the logarithm of contrail age. The observed horizontal growth during the jet and vortex phases is consistent with previous observations and contrail model results. Although the limited lifetimes of the annotated contrails prevent robust statistical conclusions for the dispersion phase, three example cases show horizontal growth rates consistent with simulations by CoCiP and that of observations in literature. Overall, this study demonstrates the potential of high-resolution LEO satellites to create observational datasets for evaluating and improving models of contrail formation and early evolution.