ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-7893-2012 Sensitivity of radiative properties of persistent contrails to the ice water path De León R. R. 1 Krämer M. 2 Lee D. S. 1 Thelen J. C. 3 Dalton Research Institute, Manchester Metropolitan University, Manchester, UK Forschungszentrum, Jülich Institut für Energie und Klimaforschung Stratosphäre, Jülich, Germany Met Office, Exeter, UK 05 09 2012 12 17 7893 7901 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/7893/2012/acp-12-7893-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/7893/2012/acp-12-7893-2012.pdf

The dependence of the radiative properties of persistent linear contrails on the variability of their ice water path is assessed in a two-stream radiative transfer model. It is assumed that the ice water content and the effective size of ice crystals in aged contrails do not differ from those observed in natural cirrus; the parameterization of these two variables, based on a correlation with ambient temperature derived from in situ observations, allows a more realistic representation than the common assumption of fixed values for the contrail optical depth and ice crystal effective radius. <br><br> The results show that the large variability in ice water content that aged contrails may share with natural cirrus, together with an assumed contrail vertical thickness between 220 and 1000 m, translate into a wider range of radiative forcings from linear contrails [1 to 66 m Wm<sup>−2</sup>] than that reported in previous studies, including IPCC's [3 to 30 m Wm<sup>−2</sup>]. Further field and modelling studies of the temporal evolution of contrail properties will thus be needed to reduce the uncertainties associated with the values assumed in large scale contrail studies.

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