Representation of the convective atmospheric boundary layer during cold-air outbreaks in regional models: a joined study based on observations, Large Eddy Simulation and mesoscale modelling

极地和中纬度地区大气过程之间的相互作用受到冷空气爆发的强烈影响。在这些事件中，来自（海）冰覆盖地区的冷空气被远距离输送到低纬度地区，而在开阔水域上空，形成了一个浅而强烈加热的对流边界层。虽然目前的天气和区域气候模式在质量上很好地捕获了CAO，但由于模式中多尺度物理CAO过程的不确定性，存在不足。悬而未决的问题涉及在开放和部分冰覆盖的海洋上的强热强迫条件下以及在非平稳天气条件下翻滚的产生。其他问题与强湍流通量的参数化有关，特别是在粗网格分辨率下。因此，本项目旨在利用大涡模拟（LES）和中尺度模式研究具有滚动涡的极地cao的物理过程。此外，CAOs湍流的参数化将得到改进，重点关注最现代的低阶闭包及其在区域尺度模式中的适用性。为此目的，在不同分辨率的中尺度模式中使用了当前和新的闭包，并将其结果与观测结果和LES结果进行了比较。

The interaction between atmospheric processes in polar and mid-latitude regions is strongly affected by cold-air outbreaks (CAOs). During such events cold air originating from (sea)ice covered regions is transported over large distances towards lower latitudes, while over open water a shallow but strongly heated convective boundary layer develops. Although the present generation of weather and regional climate models captures CAOs qualitatively well, there are deficiencies caused by uncertainties in the representation of the multi scale physical CAO processes in models. Open questions concern e.g., the generation of rolls under conditions of strong thermal forcing over the open and partially ice covered ocean and under nonstationary synoptic conditions. Other questions are related to the parameterization of the strong turbulent fluxes, especially in coarse grid resolution. Hence this project aims to study the physical processes in polar CAOs with roll vortices using large eddy simulation (LES) and mesoscale modelling. Furthermore, parameterizations of turbulence in CAOs will be improved with a focus on the most modern low order closures and their applicability to regional scale models. To this end current and new closures are used in a mesoscale model with different resolutions and its results are compared with observations and with the results of LES.