Breaking the tropical convection "dead-lock": Scale interactions of deep convection and tropical circulation

该项目将利用最先进的模型和观测分析热带对流风暴和大尺度热带波的特性。这项工作将通过分析热带大气动力学中的尺度相互作用，促进我们对地球气候系统的理解。与气象局密切合作，利用他们新的“k尺度”建模能力，我们将解决长期存在的问题，在气候循环的理解。湿对流与大尺度环流的相互作用是跨时间尺度预测的一个限制因素。在世界气候研究计划（WCRP）的“云、环流和气候敏感性”大挑战中，强调了气候变化下对流与环流的耦合是一项重大挑战。过去的项目已经显示出显式建模对流在允许新的见解，这个困难的问题在大域的价值。热带地区是地球气候的“发动机室”：太阳能加热在陆地和海洋表面的赤道地区最大化，并通过对流传递到大气层中。热带对流主要由积雨云风暴控制，积雨云风暴不仅带来降雨，而且产生强烈的大气加热，然后通过波传递到更广泛的大气。几十年来，这些湿对流风暴的表示一直在天气和气候建模中造成“僵局”，因为由于它们的尺度很小，不可能在全球模型中直接对其进行建模。这就是为什么热带地区的数值天气预报技术很低，以及对季风等主要气候系统的降雨量的气候变化预测非常不确定的一个主要原因。计算机能力的提高正在消除这种“僵局”。热带对流本质上是混沌的，但对流的可预测性和组织性是由更大尺度的传播波、与大陆尺度环流（如季风）的相互作用以及陆地和海洋表面的过程提供的。了解湿对流如何与更大规模的流动相互作用是更具挑战性的，因为在热带地区产生上升和降雨的积雨云风暴在全球模式中没有明确解决，全球模式的网格间距约为10或100公里。这意味着它们的影响通常由称为参数化的简化表示，这导致风暴与环境相互作用的方式出现重大错误。这是第一次，计算能力使我们能够运行全球或泛热带模拟，具有足够小的网格间距（约1至5公里），以明确捕捉这些风暴。该项目将解决以下科学目标：（1）潮湿对流如何与热带波相互作用，这是如何影响对流的表示，以及预测的含义。(2)湿对流如何影响大区域的水和能量平衡。(3)评估云和对流过程在气候变化中的作用。我们预计工作将包括：分析k尺度模拟中的云和风暴特性，以及它们与大尺度风和热力学中“驱动因素”的关系;将模拟行为与卫星和地面观测进行比较;诊断热带波模式及其受对流的调制;使用涡度等特性来量化对流和波之间的“尺度相互作用”;侧重于风暴生命周期的关键方面，例如风暴的发生、加强、传播和环流，其结果将指导未来天气和气候预测模式的开发和使用。通过利用英国气象局运营模型中独特的新模拟。

This project will analyse the properties of tropical convective storms and larger-scale tropical waves, in state of the art models and in observations. The work will advance our understanding of the Earth's climate system, through analysis of scale interactions in tropical atmospheric dynamics. Working closely with the Met Office and making use of their new "k-scale" modelling capability, we will address long-standing problems in the understanding of climate circulation. The interaction of moist convection with larger-scale circulations is a limiting factor for predictions across time scales. The coupling of convection with circulation under climate change is highlighted as a grand challenge in the "Clouds, Circulation and Climate Sensitivity" Grand Challenge of the World Climate Research programme (WCRP). Past projects have shown the value of explicitly modelling convection over large domains in allowing new insights to this difficult problem. The tropics are the "engine room" of Earth's climate: solar heating is maximised in equatorial regions at the land and ocean surface, and transmitted higher into the atmosphere by convection. Tropical convection is dominated by cumulonimbus storms that not only deliver rainfall, but generate intense atmospheric heating, which is then communicated to the wider atmosphere by waves. For decades the representation of these moist convective storms has provided a "deadlock" in weather and climate modelling, as it has been impossible to model them directly in a global model due to their small scale. This is one major reason why skill of numerical weather prediction is low in the tropics, and climate change projections of rainfall are very uncertain, for major climatic systems like the monsoons. Increased computer power is now removing this "dead-lock". Tropical convection is intrinsically chaotic, but some predictability and organisation of the convection is provided by larger-scale propagating waves, by interaction with continental-scale circulations such as monsoons, and through processes at the land and sea surface. Understanding how moist convection interacts with larger scale flows is made much more challenging by the fact that the cumulonimbus storms that generate ascent and rainfall in the tropics are not explicitly resolved in global models, which have grid-spacings of approximately 10s or 100s of kilometres. This means their effects are normally represented by simplifications known as parametrisations, which lead to significant errors in the way that storms interact with their environment. For the first time, computational power enables us to run global or pan-tropical simulations that have a small enough grid-spacing (approximately 1 to 5 km) to explicitly capture these storms.The project will address the following scientific objectives:(1) How moist convection interacts with tropical waves, how this is affected by the representation of convection, and the implications for predictions.(2) How moist convection influences the water and energy balance of large regions.(3) Evaluating the role of clouds and convective processes in a changing climate.We anticipate that the work will include:Analysis of cloud and storm properties in the k-scale simulations, and their relationship to "drivers" in large-scale winds and thermodynamics;Comparison of modelled behaviour with satellite and surface-based observations;Diagnosis of tropical wave modes and their modulation by the convection;Use of properties such as vorticity to quantify "scale interactions" between convection and waves;Focus on key aspects of storm life-cycles, such as initiation, intensification, propagation and circulation.The results will guide the development and use of the weather and climate prediction models of the future. By capitalising on unique new simulations from the Met Office's operational model.