Sensitivity of radiative properties of persistent contrails to the ice water path

摘要

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