Transitions Between Suppressed and Active Convection Coupled to Large-Scale Tropical Circulations

热带的天气和气候以对流为主。对流将地球表面的加热和蒸发传递给大气的其余部分。了解热带对流的位置、时间和强度对于了解全球气候系统至关重要。天气预报和气候预测模式的准确和可靠的模拟需要对流过程及其与大尺度流特征的相互作用的忠实表示。热带地区的气象学深受跨越数千公里的大规模相干运动的影响。然而，驱动这种运动的能量来源是与数百米尺度上的对流运动相关的潜在加热。因此，对流和大尺度气流之间的双向相互作用是热带气象学的关键。相关的过程在大范围的时间和空间尺度上运行，也许部分原因是它们没有被用于天气和气候研究的数值模式很好地捕捉到。数值模式不能明确地表示所有空间和时间尺度上的大气过程。相反，必须使用参数化方案来考虑短尺度的运动。一个模型将包含若干这样的方案，每一个方案都试图表示被省略的某一特定小规模过程对模型比例尺的影响。这些过程包括大气边界层湍流、重力波和对流。云解析模型（CRM）是研究对流的有力工具。这种模式可以用来进行高分辨率的对流模拟，其中对流不是参数化的，而是显式模拟的。通常通过与CRM模拟结果的比较来开发和测试参数化方案。然而，CRM模拟通常是通过规定大规模循环来建立的。因此，它们通常用于检查对流对预定情况的响应。这种模拟在对流和大尺度之间做出了明显的区分。在现实中，没有如此明显的区别；事实上，对流与大尺度环流之间存在很强的双向相互作用。因此，客户关系管理的模拟存在过度约束：可能的响应有限，不适合研究交互机制。近年来，已经发展了许多技术来近似大尺度热带环流对与对流有关的加热的响应。这些近似为模拟CRM内对流和大尺度环流之间的相互作用提供了基础。这意味着大尺度不再需要在模拟中指定，而是根据显式模拟的对流而进化。使用这些近似的研究产生了一些有价值和有趣的结果。在这个项目中，我们将评估其中一些方法对热带对流不同问题的相对优点，并利用它们来研究对流和大尺度环流之间的相互作用在热带变率中的作用。我们还将应用相同的框架来评估现有对流参数化方案的行为，为大气建模界提供一个精心控制和严格测试天气和气候模型的新范例。

The weather and climate of the tropics is dominated by convection. Convection communicates to the rest of the atmosphere the heating and evaporation at the earth's surface. Understanding the location, timing and strength of tropical convection is crucial for understanding the global climate system. Accurate and reliable simulations by both weather-forecast and climate-prediction models require a faithful representation of convective processes and their interactions with features in the large-scale flow. The meteorology of the tropics is profoundly affected by large-scale coherent motions across thousands of kilometres. However, the energy source driving such motions is the latent heating associated with convective motions on scales of hundreds of metres. Thus, the two-way interactions between convection and large-scale flow are key to tropical meteorology. The relevant processes operate across a wide range of time and space scales and perhaps partly for that reason they are not well-captured by the numerical models used for weather and climate studies. The numerical models are incapable of representing explicitly the atmospheric processes on all space and time scales. Rather motions with short scales must be taken into account by using parameterization schemes. A model will contain a number of such schemes, each attempting to represent the effects on the model scales of a particular small-scale process that has been omitted. These processes will include turbulence in the atmospheric boundary layer, gravity waves and convection.A powerful tool for studying convection is the Cloud Resolving Model (CRM). Such models can be used to perform high-resolution simulations in which the convection is not parameterized but is explicitly modelled. Parameterization schemes are often developed and tested through comparisons with the results of CRM simulations. However, the CRM simulations are typically set up by prescribing a large-scale circulation. Thus, they are generally used to examine the response of the convection to a pre-defined situation. Such simulations make a sharp distinction between the convection and the large-scale. In reality, there is no such sharp distinction; indeed, there are strong two-way interactions between convection and the large-scale circulation. As a result, the CRM simulations are over-constrained: limited in their possible responses and unsuited for studying the interaction mechanisms.In recent years, a number of techniques have been developed for approximating the response of the large-scale tropical circulation to the heating associated with convection. These approximations provide a basis for modelling the interactions between convection and the large-scale circulation within a CRM. This means that the large-scale no longer has to be prescribed in the simulation but instead it will evolve in response to the explicitly simulated convection. Studies using these approximations have produced some valuable and intriguing results. In this project we will assess the relative merits of some of these approaches for different problems in tropical convection and exploit them to investigate the role of interactions between convection and the large-scale circulation in tropical variability.We will also apply this same framework to assess the behaviour of existing convection parameterization schemes, providing the atmospheric modelling community with a new paradigm for carefully-controlled and rigorous testing of weather-and-climate models.