Abstract
Abstract. Contrail–cirrus is probably the largest climate forcing from aviation. The evolution of contrail–cirrus and its radiative impact depends not only on a multitude of atmospheric parameters, but also on the geometric and microphysical properties of the young contrails evolving into contrail–cirrus. The early evolution of contrails (t < 5 min) 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 depend on many environmental and aircraft parameters. Both properties, H and N, affect the later properties of the evolving contrail–cirrus, as they control the extent of shear-induced spreading and sedimentation losses. In this study, we provide parametrisations of H and N after 5 min taking into account the effects of temperature, relative humidity, thermal stratification and aircraft type (mass, wing span, fuel burn). The parametrisations 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 affect the contrail evolution during the vortex phase.
Highlights
1.1 MotivationContrail–cirrus is probably the largest contribution from aviation to climate change in terms of radiative forcing (Burkhardt and Kärcher, 2011)
Both processes have an impact on the evolution of the contrail–cirrus while it spreads by vertical wind shear and produces a fall streak by sedimentation
The present study develops and provides a parametrisation for the depth and crystal number of young contrails, which accounts for the important physics and considers the dominant parameters, namely relative humidity, temperature, thermal stratification and aircraft parameters
Summary
Contrail–cirrus is probably the largest contribution from aviation to climate change in terms of radiative forcing (Burkhardt and Kärcher, 2011). Adiabatic heating may result in strong crystal loss Both processes have an impact on the evolution of the contrail–cirrus while it spreads by vertical wind shear and produces a fall streak by sedimentation. The present study develops and provides a parametrisation for the depth and crystal number of young contrails, which accounts for the important physics and considers the dominant parameters, namely relative humidity, temperature, thermal stratification and aircraft parameters. S. Unterstrasser: Properties of young contrails based on LES very roughly captured. Unterstrasser: Properties of young contrails based on LES very roughly captured This approach exhibits a way to condense information gained from LESs such that it finds its way into global-scale models. The present approach complements a parametrisation describing the long-term contrail–cirrus evolution in Lewellen (2014) where the ice crystal number is an important input parameter
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