Behaviour of convective updraughts: A challenging problem for weather and climate models

该项目的目的是：增进对决定对流上升气流时间演变的物理过程的了解。例如，我们认为云是由热量组成的；请参见下面的示意图，并与真实云的照片进行比较。但是，这个示意性模型如何才能被表示为一个理想化的模型，从而形成天气和全球气候模型中表示的基础？这位博士生可能会发现这个问题很有趣，也很有挑战性。也许有一种不同的方式来表示云，比如羽毛？需要考虑的具体问题包括：云核区的大小和其中的液体数量，以及这些随时间的变化？这个核心区和云边缘的下降空气之间有什么相互作用？造成混合以及整个云层环流的湍流涡旋有哪些特征？这些问题将通过对单个云和云集合的模拟来解决。对流上升气流的模拟对模式分辨率特别敏感。博士研究将包括25米分辨率的数值实验。在这种分辨率下，对流云与其环境之间的混合得到了很好的解决。一种可以在最新一代超级计算机上高效运行的新的高分辨率模型(Met Office NERC云模型，MONC)的出现，现在使在大范围内进行这样的模拟成为可能，从而可以研究云的集合。这是一个非常令人兴奋的发展：下图显示了可以使用这样的模型模拟的详细云结构的示例。数值实验可能包括对理想化的单一云团的研究，以及基于实地战役的背景下的多重云团的研究。这些现场观测的使用提供了对模型模拟的真实性的重要检查。

The aim of the project is: to improve the understanding of the physical processes that determine the time evolution of convective updraughts. For example, we believe that clouds are composed of thermals; see the schematic diagram below and compare with the photo of a real cloud. But how can this schematic model be represented as an idealised model that could form the basis of the representation in weather and global climate models? The PhD student will likely find this question to be interesting and challenging. Perhaps there is a different way of representing the clouds, as say plumes? Specific questions that need to be considered include: what is the size of the cloud core region and the amount of liquid in it, and how do these change with time? What is the interaction between this core region and the descending air at the edge of the cloud? What are the characteristics of the turbulent eddies that cause mixing, as well as the circulation of the whole cloud. These questions will be addressed by using simulations of both single clouds and collections of clouds.The simulation of convective updraughts is particularly sensitive to model resolution. The PhD research will involve numerical experiments at 25 m resolution. At this resolution, mixing between convective clouds and their environment is well resolved. The availability of a new high-resolution model (the Met Office NERC cloud model, MONC) that can efficiently run on the latest generation of supercomputers, now makes it possible to perform such simulations on large domains, such that a collection of clouds can be studied. This is a very exciting development: the figure below shows an example of the detailed cloud structures that can be simulated with such a model. Numerical experiments will likely include studies of idealized single clouds, as well as multiple clouds in a setting which is based on field campaigns. The use of these field observations provides an important check on the realism of the model simulations.