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Statistical Analysis of Contrail to Cirrus Evolution During the Contrail and Cirrus Experiment (CONCERT)

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Statistical Analysis of Contrail to Cirrus Evolution During the Contrail and Cirrus Experiment (CONCERT) Atmos. Chem. Phys., 18, 9803–9822, 2018 https://doi.org/10.5194/acp-18-9803-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Statistical analysis of contrail to cirrus evolution during the Contrail and Cirrus Experiment (CONCERT) Aurélien Chauvigné1, Olivier Jourdan1, Alfons Schwarzenboeck1, Christophe Gourbeyre1, Jean François Gayet1, Christiane Voigt2,3, Hans Schlager2, Stefan Kaufmann2, Stephan Borrmann3,4, Sergej Molleker3,4, Andreas Minikin2,a, Tina Jurkat2, and Ulrich Schumann2 1Laboratoire de Météorologie Physique, UMR 6016 CNRS/Université Clermont Auvergne, Clermont-Ferrand, France 2Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany 3Institut für Physik der Atmosphäre, Universität Mainz, Mainz, Germany 4Max Planck Institute for Chemistry, Department for Particle Chemistry, Mainz, Germany anow at: Flugexperimente, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany Correspondence: Aurélien Chauvigné ([email protected]) Received: 11 October 2017 – Discussion started: 13 October 2017 Revised: 19 June 2018 – Accepted: 20 June 2018 – Published: 12 July 2018 Abstract. Air traffic affects cloudiness, and thus climate, by erties are well suited to identify and discriminate between the emitting exhaust gases and particles. The study of the evolu- different contrail growth stages and to characterize the evo- tion of contrail properties is very challenging due to the com- lution of contrail properties. plex interplay of vortex dynamics and the atmospheric envi- ronment (e.g. temperature, supersaturation). Despite substan- tial progress in recent years, the optical, microphysical, and macrophysical properties of contrails and ambient cirrus dur- 1 Introduction ing contrail formation and subsequent ageing are still subject to large uncertainties due to instrumental and observational Aircraft exhaust plumes have a significant impact on climate limitations and the large number of variables influencing the and tropospheric chemistry (Lee et al., 2010; IPCC, 1999). contrail life cycle. In this study, various contrail cases cor- The Intergovernmental Panel on Climate Change IPCC Spe- responding to different aircraft types and atmospheric con- cial Report on Aviation (1999) estimates that NOx emis- ditions are investigated using a statistical method based on sions from subsonic aircraft increase ozone concentrations the in situ optical measurements performed during the Con- at cruise level. Short- and long-lived pollution species have trail and Cirrus Experiments (CONCERT) campaigns 2008 different impacts on atmospheric chemical composition de- and 2011. The two aircraft campaigns encompass more than pending on the flight level (Frömming et al., 2012). Emis- 17 aircraft contrail cases. A principal component analysis sions of water vapour, black carbon (BC) or soot particles, (PCA) of the angular scattering coefficients measured by the sulfate (SO4) aerosols, and nitrogen oxides (NOx) contribute polar nephelometer is implemented. The goal is to classify to the modification of the chemical composition of the upper the sampled ice cloud measurements in several clusters rep- troposphere on shorter timescales (Lee et al., 2010; Gettel- resentative of different contrail development stages (primary man and Chen, 2013; Liou et al., 2013). The long-term cli- wake, young contrail, aged contrail, and cirrus). Extinction mate impact is mainly driven by CO2 emissions. Modelling and asymmetry coefficients, nitrogen oxide concentrations, studies have shown that the direct radiative forcing from avi- − and relative humidity with respect to ice and particle size ation is expected to represent 3–4 % (50–60 mW m 2) of distributions are analysed for each cluster to characterize the the anthropogenic forcing (Lee et al., 2010; De León et al., − evolution of ice cloud properties during the contrail to cirrus 2012) and could reach 87 mW m 2 in 2025 (Chen and Gettel- evolution. The PCA demonstrates that contrail optical prop- man, 2016). Aircraft-induced cloudiness also has an impor- tant impact on climate, although the quantitative assessment Published by Copernicus Publications on behalf of the European Geosciences Union. 9804 A. Chauvigné et al.: Statistical Analysis of Contrail to Cirrus Evolution of the radiative forcing remains a major source of uncertain- take of water vapour as long as saturation with respect to ice ties (Lee et al., 2010). prevails. In ice-saturated conditions, contrails can persist af- ter the vortex breakdown, spread, and evolve into contrail cir- 1.1 Contrail formation and evolution rus (Schumann and Heymsfield, 2017). The associated cloud cover (larger than for linear contrails alone) increases the Contrail formation is mainly controlled by the thermody- radiative forcing of contrail cirrus (Burkhardt and Kärcher, namic properties of the ambient air and by the aircraft emis- 2011; Schumann et al., 2015). sions. The conditions for contrail formation can be deter- mined by the Schmidt–Appleman criterion (SAC) (Schu- 1.2 Optical and microphysical properties of mann, 1996). Contrail chemical composition can have a sig- contrail phases nificant impact on the contrail formation (Kärcher and Yu, 2009). Indeed, contrail microphysical properties such as the The assessment of the contrail radiative forcing requires, in total number densities and ice crystal diameters are directly particular, an accurate estimation of the cloud cover, the vis- linked to the emission index (e.g. soot emission index in ible optical depth, the single-scattering characteristics, and kg fuel−1). Several studies in the past have been dedicated to the ice crystal effective size and habit (Yang et al., 2010; the evolution of concentrations of nitrogen oxide (NO) and Spangenberg et al., 2013). Satellite observations provide a sulfur dioxide (SO2) and their oxidized forms (Kärcher and comprehensive dataset to study the contrail to cirrus evolu- Voigt, 2006; Voigt et al., 2006; Schäuble et al., 2009; Jurkat tion statistically. The combined contrail tracking algorithms et al., 2011). on the Spinning Enhanced Visible and Infrared Imager (SE- Two different processes of contrail formation have been VIRI) on board the Meteosat Second Generation (MSG) studied: combustion condensation trails and aerodynamic satellites with properties inferred by the Moderate Imag- condensation trails. Different studies (Gierens and Dilger, ing Spectroradiometer (MODIS) on board the Terra satellite 2013; Jansen and Heymsfield, 2015) have illustrated char- were used by Vázquez-Navarro et al. (2015) to character- acteristics of aerodynamically controlled contrail formation ize the properties of 2300 contrails. Properties included the associated with warmer temperatures (observations at tem- lifetime (mean values of 1 h), the length (130 km), the op- peratures above −38 ◦C). Contrails primarily initiated by the tical thickness (0.34), the altitude (11.7 km), and the radia- combustion processes result from the mixing of hot and hu- tive forcing (−26 W m−2 for shortwave forcing over land) of mid exhaust gases with cooler and dryer ambient air. This these contrails. increases the local relative humidity in the exhaust plume However, detailed in situ optical and microphysical mea- leading to the formation of contrails when the saturation with surements are still needed to evaluate satellite products and to respect to liquid water is reached. In this case, soot and sul- develop a more appropriate retrieval algorithm. Distinguish- fate aerosols emitted by the aircraft (Moore et al., 2017) may ing contrails from natural cirrus from satellite observations act as condensation nuclei to form liquid droplets. Homoge- remains extremely challenging. Although the optical and mi- neous ice nucleation of the liquid droplets can occur when the crophysical properties of young contrails (linear contrails) exhaust cools down through mixing with the ambient temper- differ from natural cirrus properties, the contrail properties ature, while preserving ice saturation. Small ice crystals are are highly time dependent, and persistent contrail cirrus can then formed in the jet phase within some tenths of a second be embedded in thin cirrus clouds. Recent in situ measure- (Kärcher and Yu, 2009). ments (Voigt et al., 2017) show that the microphysical prop- The life cycle of contrails depends on their interaction erties of contrail cirrus can still be distinguished from natural with the wake vortices behind aircraft and the ambient at- cirrus at contrail cirrus ages up to several hours. mosphere (Irvine et al., 2012; Graf et al., 2012; Duda et Most of the previous studies (Jeßberger et al., 2013; al., 2013; Carleton et al., 2013; Schumann and Heymsfield, Lewellen, 2012; Schumann et al., 2013) divide the contrail 2017). The ice crystals in the young contrails are captured analysis into the two wakes phases. Primary and secondary within two counter-rotating wake vortices in the downwash wake properties depend strongly on atmospheric conditions behind the aircraft induced by the aircraft lift; these vortices and aircraft type (emission index, vortex, flight level, ambient induce adiabatic compression, heating, and partial sublima- humidity, temperature, etc.). In the primary wake, contrail ice tion of the ice crystals within the primary wake (Lewellen crystals are quasi-spherical with values of the effective diam- and Lewellen, 2001; Sussmann and Gierens, 2001; Unter- eter (Deff) typically
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