Atmos. Chem. Phys. Discuss., 9, 14955-14993, 2009
www.atmos-chem-phys-discuss.net/9/14955/2009/
doi:10.5194/acpd-9-14955-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Numerical simulations of contrail-to-cirrus transition – Part 2: Impact of initial ice crystal number, radiation, stratification, secondary nucleation and layer depth
S. Unterstrasser and K. Gierens
Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. Simulations of contrail-to-cirrus transition were performed with an LES model. In Part 1 the impact of relative humidity, temperature and vertical wind shear was explored in a detailed parametric study. Here, we study atmospheric parameters (like stratification and depth of the supersaturated layer) and processes which may affect the contrail evolution. Under suitable conditions (controlled by the radiation scenario and stratification) radiative heating lifts the contrail-cirrus and prolongs its lifetime. The radiation scenario affects the radiance incident on the contrail layer and is characterised herein by the season, time of day and the presence of lower-level cloudiness. The potential of contrail-driven secondary nucleation, both via heterogeneous nucleation of preactivated soot cores (from former contrail ice crystals) and homogeneous nucleation is investigated. It turned out that in our model the pure contrail dynamics (triggered by radiative heating) does not suffice to force homogeneous freezing of ambient liquid aerosol particles. Our model results suggest that heterogeneous nucleation of preactivated soot cores is unimportant mainly because the relative humidity does not exceed ice saturation substantially close to the contrail core. Contrail evolution is not controlled by the depth of the supersaturated layer as long as it exceeds roughly 500 m. Deep fallstreaks however need thicker layers. A variation of the initial ice crystal number is effective during the whole evolution of a contrail which implies that engine modifications that lead to lower soot emissions would lead to optically thinner and shorter living contrail-cirrus.

Citation: Unterstrasser, S. and Gierens, K.: Numerical simulations of contrail-to-cirrus transition – Part 2: Impact of initial ice crystal number, radiation, stratification, secondary nucleation and layer depth, Atmos. Chem. Phys. Discuss., 9, 14955-14993, doi:10.5194/acpd-9-14955-2009, 2009.
 
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