Three-dimensional Large Eddy Simulations of contrail ice crystal formation with an improved representation of aerosol and ice microphysics

尾迹卷云（由年轻和年老的尾迹组成）是已知的由航空引起的人为全球变暖的最大贡献者。形成的尾迹冰晶的数量，特别是由发动机烟灰数量排放和大气条件决定的，可以对进一步的尾迹卷生命周期、性质及其辐射影响产生强烈影响。到目前为止，有两种互补的方法来模拟喷射阶段尾迹的形成。目前的三维研究主要集中在射流动力学上，而以前的三维研究主要集中在射流羽流的微物理过程上。该项目的基本目标是结合这两种方法的优点，即通过三维大涡模拟（LES）和改进的尾迹冰微物理表示来模拟商用飞机后面的尾迹形成。在模型开发方面，最初为自然冰云开发的拉格朗日冰微物理（LCM）代码必须通过尾迹冰晶形成进行扩展，并与支持可压缩流动现象的最新EULAG版本相结合。3D LES的一个主要目标是分析在不同大气条件下可能形成尾迹的排气羽流中冰晶形成的时空演变。因此，对流层上层背景气溶胶颗粒的夹带，也可以在羽流中形成冰晶，将首次在三维模型中被考虑。在LES计算的基础上，推导出尾迹冰晶形成的启发式参数化，并将其整合到全球气候模式ECHAM5中。这应该与已经存在的旋涡阶段冰晶损失的参数化联系起来，以便改进气候模式中尾迹的初始化。在全球模拟中，将更详细地研究参数化过程及其对不同气象条件下尾迹云特性的影响。最后，一个重要的目标是分析减少烟灰数量排放（因为它们可以通过在巡航飞行中使用替代燃料混合物来实现）对尾迹冰晶形成的影响，并在全球气候模式内调查这种对尾迹卷云特性及其气候影响的影响。

Contrail cirrus (consisting of young and aged contrails) are the largest known contributor to the anthropogenic global warming caused by aviation. The number of formed contrail ice crystals, which is particularly determined by engine soot number emissions and atmospheric conditions, can have a strong influence on the further contrail cirrus life cycle, properties and their radiative impact.So far, there are two complementary approaches to simulate the formation of contrails during the jet phase. While current 3D studies focus on the jet dynamics, the previous 0D approaches concentrate on microphysical processes in the jet plume. The basic objective of this project is to combine the benefits of these two approaches which means to simulate contrail formation behind commercial aircraft by means of three-dimensional Large Eddy Simulations (LES) with an improved representation of contrail ice microphysics. Concerning the model development, the Lagrangian Ice Microphysics (LCM) code, originally developed for natural ice clouds, has to be extended by the contrail ice crystal formation and coupled to an up-to-date EULAG version that supports compressible flow phenomens. One main goal of the 3D LES is to analyze the spatial and temporal evolution of the ice crystal formation in the exhaust plume for different atmospheric conditions where contrails can form. Thereby, the entrainment of upper tropospheric background aerosol particles, which also can form ice crystals in the plume, will be considered for the first time in a 3D model. Based on the LES calculations, a heuristic parameterization for the formation of contrail ice crystals will be derived and integrated into the global climate model ECHAM5. This should be linked with an already existing parameterization of the ice crystal loss during the vortex phase in order to improve the initialization of contrails in the climate model. Within the global simulations, both parametrized processes and their effects on contrail cirrus properties dependent on different meteorological conditions will be investigated in more detail. Finally, an important objective is to analyze the influence of reduced soot number emissions (as they can be realized by the use of alternative fuel blends in cruise flight) on the formation of contrail ice crystals and, within the global climate model, to investigate this influence on contrail cirrus properties and their climate impact.