CoDyPhy: Improved Coupling of Dynamics and Physics for understanding and modelling moist convection

湿对流是用来描述云内垂直传输的术语，云的浮力是由水蒸气凝结时释放的潜热产生的。湿对流是影响地球大气中天气和气候的主要过程之一。然而，尽管经过几十年的努力，在用于天气和气候预测的计算机模型中表示对流系统仍然存在重大挑战。常见的错误和偏差包括无法模拟对流和辐射冷却之间的物理正确平衡，海洋和热带陆地上空对流的不切实际的昼夜循环，热带地区不切实际的快速和弱对流耦合大尺度波，模拟对流在空间和时间上的虚假强不稳定性，以及在模式格点尺度上出现过于剧烈的“格点风暴”。拟议的项目旨在提高我们在天气预报和气候模式中代表湿对流的能力。这将通过更好地理解对流如何与大气环流在小尺度和大尺度上相互作用，并通过发展一种新的方法来表示对流的数值模式来实现。对流与大气环流的相互作用是非常复杂的，人们对此知之甚少。它涉及许多不同的反馈机制，包括大尺度动力学和输送、大气边界层和地面通量以及辐射过程。我们的工作将集中在热带环流：哈德利环流和热带辐合带，步行者环流，对流耦合波。我们将通过使用一个简化的全球环流模型来进行仔细控制的假设检验实验和敏感性测试，以提高对这些相互作用的理解。这里的目的不是尽可能准确地模拟这些循环，而是通过分离最重要的过程，诊断机制和量化敏感性来提高理解。这项模拟工作将得到一个新的理论模型的补充，该模型描述了对流与大气边界层和大尺度环流的相互作用。这个新的理论模式将被应用于理解边界层在确定步行者环流结构中的作用。这项工作的第三条链将是使用理论和数值模式来理解边界层在影响对流的日循环中的作用。全球天气预报模式和气候模式目前分别使用粗于10公里和几十公里量级的网格分辨率。所谓的“动力核心”的模式预测风和温度场的演变，在这些解决尺度。然而，典型的对流云水平尺度约为1公里。因此，这种模式不能解决个别对流云。相反，对流是由一个次网格模型或“参数化”计划，试图模拟对流的影响，解决尺度。在这里，我们提出了一种新的方法来表示对流，其中单独的风场和温度场的非对流流体和对流流体的动力核心预测。我们将扩展这种双流体模型的理论理解，我们将在三维计算机模型中实现它，我们将在一系列日益复杂的测试中评估其性能。这种新的对流表示有可能克服传统对流方案的几个长期存在的局限性。

Moist convection is the term used to describe the vertical transport within clouds whose buoyancy is produced by the latent heat released when water vapour condenses. Moist convection is one of the dominant processes affecting the weather and climate in Earth's atmosphere. However, despite decades of effort, there remain major challenges in representing convective systems in the computer models used for weather and climate prediction. Common errors and biases include an inability to simulate a physically correct equilibrium between convection and radiative cooling, an unrealistic diurnal cycle of convection over ocean and over tropical land, unrealistically fast and weak convectively-coupled large-scale waves in the tropics, spuriously strong intermittency of modelled convection in space and time, and the occurrence of excessively violent `grid point storms' at the scale of the model grid.The proposed project aims to improve our ability to represent moist convection in weather prediction and climate models. This will be achieved through an improved understanding of how convection interacts with the atmospheric circulation on small and large scales, and through the development of a novel way of representing convection in numerical models.The interaction of convection with the atmospheric circulation is extremely complex and poorly understood. It involves many different feedback mechanisms, including large scale dynamics and transport, the atmospheric boundary layer and surface fluxes, and radiative processes. Our work will focus on tropical circulations: the Hadley circulation and InterTropical Convergence Zone, the Walker circulation, and convectively coupled waves. We will improve understanding of these interactions by using a simplified model of the global circulation to carry out carefully controlled hypothesis testing experiments and sensitivity tests. The aim here is not to simulate these circulations as accurately as possible, but to improve understanding by isolating the most important processes, diagnosing mechanisms, and quantifying sensitivities. This modelling work will be complemented by the development of a new theoretical model describing the interaction of convection with the atmospheric boundary layer and the larger scale circulation. This new theoretical model will be applied to understanding the role of the boundary layer in setting the structure of the Walker circulation. A third strand of this work will be to use theory and numerical models to understand the role of the boundary layer in influencing the diurnal cycle of convection.Global weather forecast models and climate models currently use grid resolutions coarser than 10km and of order several 10's of km, respectively. The so-called `dynamical core' of the model predicts the evolution of wind and temperature fields at these resolved scales. Typical convective clouds, however, have a horizontal scale of order 1km. Therefore, such models cannot resolve individual convective clouds. Instead, convection is represented by a subgrid model or `parameterization' scheme that attempts to model the effects of convection on the resolved scales. Here we propose a new approach to representing convection, in which separate wind and temperature fields for non-convecting fluid and convecting fluid are predicted by the dynamical core. We will extend the theoretical understanding of this two-fluid model, we will implement it in a three-dimensional computer model, and we will evaluate its performance in a series of tests of increasing complexity. This new representation of convection has the potential to overcome several long-standing limitations of conventional convection schemes.