GENESIS: Dynamics and parametrisation of deep convective triggering, maintenance and updraughts

在物理上，深层对流是大气中的一个关键过程，特别是在热带地区，它是天气的主要驱动力，在强迫全球环流方面发挥着关键作用。尽管对流在大尺度上起着关键作用，但对流本质上是一个相对小尺度的过程，对流云通常在100米到几公里的尺度上，因此在全球数值天气预报（NWP）和气候模式中无法解决。因此，对流的“参数化”对于准确地表示对流对更大尺度流动的影响至关重要。这不是一个简单的问题，当前对流参数化方案的缺陷导致了显著的模式偏差、热带对流的错误日循环（对降雨和辐射地表加热产生连锁效应）以及对重要大气环流（如由对流驱动的Madden-Julien振荡）的不充分表征。造成这些缺陷的两个特殊的、相互关联的问题是对流的触发（时间、位置和触发的随机性）和随后对流组织成更大的对流系统。该项目的总体目标是汇集我们对控制深层对流触发和组织的各种物理过程的理解，并利用这一点来开发一个框架，在这个框架中，这些过程可以以一致的方式集成。这样一个框架将使这些重要的过程能够在新的对流参数化方案中以更实际和一致的方式表示。特别是，基于物理的对流触发方案应该更容易集成到正在开发的新一代随机对流参数化方案中。这样的方案也更容易实现尺度感知，即适应模型分辨率，只参数化必要的子网格过程，同时允许模型解析对流的更大规模特征。这对于最新的NWP和区域气候模式模拟尤其重要，因为它们具有足够高的分辨率，可以明确地表示对流，尽管相当粗糙。当前参数化方案的另一个限制是它们往往是瞬时的。在有对流组织的地方，系统具有“记忆”，即对流的发生和组织将影响进一步对流的局部发展。我们将使用流体动力学其他分支的技术来理解和量化对流系统中的组织，并开发可作为新的随机对流参数化基础的措施。这个项目将考虑内部过程和外部过程。由对流本身产生的内部过程，如重力波和冷池，在对流的触发和组织中起着关键作用。在陆地上，表面非均质性和地形等外部因素在触发对流和控制对流如何组织方面也起着重要作用。将这些不同的相互竞争的影响整合到一个一致的框架中，将是参数化方案向前迈出的重要一步。通过英国气象局统一模型（MetUM）和英国气象局- nerc云解析模型（MONC）的理想化数值模拟，研究了单个过程的框架，我们将在更现实的大域模拟中测试这些想法，以帮助量化小尺度对流和大尺度场之间重要的尺度相互作用。该项目的产出将是一系列基于物理的通用模型框架，这些框架可作为本项目和国际上正在提出或开发的不同对流参数化方案的组成部分

Physically, deep convection is a key process in the atmosphere, particularly in the tropics, where it is the dominant driver of the weather as well as playing a key role in forcing global circulation. Despite this key role on the large scale, convection is inherently a relatively small-scale process with convective clouds typically being on the scale of 100's of metres to a few kms, and therefore unresolved in global numerical weather predicition (NWP) and climate models. "Parametrisation" of convection is therefore critical to accurately represent the impact of convection on the larger scale flow. This is not a simple problem, and deficiencies in current convective parametrisation schemes lead to significant model biases, the wrong diurnal cycle of convection in the tropics (with knock-on effects on rainfall and surface heating by radiation) and inadequate representation of important atmospheric circulations such as the Madden-Julien Oscillation, which are driven by convection. Two particular, and linked, problems which contribute to these deficiencies are the triggering of convection (timing, location and the stochastic nature of triggering) and the subsequent organisation of convection into larger convective systems.The overarching aim of this project is to bring together our understanding of the various physical processes which control the triggering and organisation of deep convection, and to use this to develop a framework in which these processes can be integrated in a consistent way. Such a framework will allow these important processes to be represented in new convective parametrisation schemes in a more physically realistic and consistent manner. In particular, a physically-based convective triggering scheme should be easier to integrate into the new generation of stochastic convective parametrisation schemes which are being developed. Such schemes will also be easier to make scale-aware, i.e. to adapt with the model resolution to only parametrise the necessary sub-grid processes, while allowing the model to resolve larger-scale features of the convection. This is particularly important for the latest NWP and regional climate model simulations which are of sufficiently high resolution that they permit the explicit representation of convection, albeit rather crudely. A further limitation of current parametrisation schemes is that they tend to be instantaneous. Where convection organised, the system has "memory", i.e. the occurrence and organisation of convection will impact on the local development of further convection. We will use techniques from other branches of fluid dynamics to understand and quantify organisation in convective systems and develop measures which can be used as the basis for new stochastic convection parametrisations.This project will consider both internal processes and external processes. Internal processes generated by the convection itself, such as gravity waves and cold pools, play a key role in the triggering and organisation of convection. Over land external factors such as surface heterogeneity and topography also play an important role in triggering convection and controlling how it can organise. Integrating these various competing influences into a consistent framework will be a significant step forward for parametrisation schemes. Having developed the framework from studying individual processes through idealised numerical simulations with the Met Office Unified Model (MetUM) and the Met Office-NERC cloud resolving model (MONC) we will test the ideas in more realistic large-domain simulations to help quantify the important scale interactions between small scale convection and the larger scale fields. The output of this project will be a series of generic physically-based model frameworks which can be used as components in different convective parametrisations schemes which are being proposed or developed, both within this programme and internationally