Note: Covert aerosol climate engineering takes advantage of the warming effect produced by contrail-cirrus cloud formation as described below. But like contrail-cirrus on steroids, chemical trails secretly deployed by aircraft are able to force climate warming more aggressively than contrail-cirrus, since the aerosol chemistry produces a darker cloud where albedo (sunlight reflection into space) is non-existent/negative and the resulting effect of long-wave radiation entrapment as “overcast” is significantly enhanced. (H Saive)
Contrail-cirrus is probably the largest climate forcing of aviation. The evolution of contrail-cirrus and their radiative impact depends on a multitude of atmospheric parameters, but also on the geometric and microphysical properties of the young contrails evolving into 5 contrail-cirrus. The early evolution of contrails (t < 5min) is dominated by an interplay of ice microphysics and wake vortex dynamics. Young contrails may undergo a fast vertical expansion due to a descent of the wake vortices and may lose a substantial fraction of their ice crystals due to adiabatic heating. The geometric depth H and total ice crystal number N of young contrails are highly variable and de10 pend on many environmental and aircraft parameters. Both properties, H and N, aect the later properties of the evolving contrail-cirrus, as they control the extent of shearinduced spreading and sedimentation losses. In this study, we provide parametrisations of H and N after 5 min taking into account the eects of temperature, relative humidity, thermal stratification and aircraft type (mass, wing span, fuel burn). The parametri15 sations rely on a large data set of recent large-eddy simulations of young contrails. They are suited to be incorporated in larger-scale models in order to refine the present day contrail initialisations by considering the processes that strongly aect the contrail
evolution during the vortex phase.
Contrail-cirrus is probably the largest contribution of aviation to climate change in terms of radiative forcing (Burkhardt and Kärcher, 2011). However, its quantification is associated with large uncertainties and the confidence of those estimates is still rated low (Boucher et al., 2013). Contrail radiative forcing is estimated by global circulation 25 models (GCMs) whose parametrisations of contrails have been improved in the recent past. In particular, the analysis methods switched from diagnostic approaches for young (line-shaped) contrails (Ponater et al., 2002; Rap et al., 2010; Chen and Gettelman, 2013) towards a process based treatment of contrail cirrus evolution (Burkhardt and Kärcher, 2009; Schumann, 2012)