Articles | Volume 17, issue 1
Atmos. Chem. Phys., 17, 403–438, 2017

Special issue: ML-CIRRUS – the airborne experiment on natural cirrus...

Atmos. Chem. Phys., 17, 403–438, 2017
Research article
10 Jan 2017
Research article | 10 Jan 2017

Properties of individual contrails: a compilation of observations and some comparisons

Ulrich Schumann1, Robert Baumann1, Darrel Baumgardner2, Sarah T. Bedka3, David P. Duda3, Volker Freudenthaler4, Jean-Francois Gayet5, Andrew J. Heymsfield6, Patrick Minnis7, Markus Quante8, Ehrhard Raschke9, Hans Schlager1, Margarita Vázquez-Navarro1, Christiane Voigt1,10, and Zhien Wang11 Ulrich Schumann et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, 82234 Oberpfaffenhofen, Germany
  • 2Droplet Measurement Technologies Inc., Boulder, CO, USA
  • 3Science Systems and Applications, Inc., Hampton, VA, USA
  • 4Ludwig-Maximilians-Universität, Meteorologisches Institut, Munich, Germany
  • 5Laboratoire de Météorologie Physique, CNRS, Clermont-Ferrand, France
  • 6National Center for Atmospheric Research, Boulder, CO, USA
  • 7NASA Langley Research Center, Hampton, VA, USA
  • 8Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Geesthacht, Germany
  • 9Max Planck Institute for Meteorology and University of Hamburg, Hamburg, Germany
  • 10Johannes Gutenberg-Universität, Institut für Physik der Atmosphäre, Mainz, Germany
  • 11University of Wyoming, Department of Atmospheric Sciences, Laramie, WY, USA

Abstract. Mean properties of individual contrails are characterized for a wide range of jet aircraft as a function of age during their life cycle from seconds to 11.5 h (7.4–18.7 km altitude, −88 to −31 °C ambient temperature), based on a compilation of about 230 previous in situ and remote sensing measurements. The airborne, satellite, and ground-based observations encompass exhaust contrails from jet aircraft from 1972 onwards, as well as a few older data for propeller aircraft. The contrails are characterized by mean ice particle sizes and concentrations, extinction, ice water content, optical depth, geometrical depth, and contrail width. Integral contrail properties include the cross-section area and total number of ice particles, total ice water content, and total extinction (area integral of extinction) per contrail length. When known, the contrail-causing aircraft and ambient conditions are characterized. The individual datasets are briefly described, including a few new analyses performed for this study, and compiled together to form a contrail library (COLI). The data are compared with results of the Contrail Cirrus Prediction (CoCiP) model. The observations confirm that the number of ice particles in contrails is controlled by the engine exhaust and the formation process in the jet phase, with some particle losses in the wake vortex phase, followed later by weak decreases with time. Contrail cross sections grow more quickly than expected from exhaust dilution. The cross-section-integrated extinction follows an algebraic approximation. The ratio of volume to effective mean radius decreases with time. The ice water content increases with increasing temperature, similar to non-contrail cirrus, while the equivalent relative humidity over ice saturation of the contrail ice mass increases at lower temperatures in the data. Several contrails were observed in warm air above the Schmidt–Appleman threshold temperature. The emission index of ice particles, i.e., the number of ice particles formed in the young contrail per burnt fuel mass, is estimated from the measured concentrations for estimated dilution; maximum values exceed 1015 kg−1. The dependence of the data on the observation methods is discussed. We find no obvious indication for significant contributions from spurious particles resulting from shattering of ice crystals on the microphysical probes.

Short summary
The initially linear clouds often seen behind aircraft are known as contrails. Contrails are prototype cirrus clouds forming under well-known conditions, but with less certain life cycle and climate effects. This paper collects contrail data from a large set of measurements and compares them among each other and with models. The observations show consistent contrail properties over a wide range of aircraft and atmosphere conditions. The dataset is available for further research.
Final-revised paper