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

湿对流是用来描述云中垂直输送的术语，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日循环、热带地区不现实的快而弱的对流耦合大尺度波、模拟的对流在空间和时间上的异常强烈的间歇性，以及在模式网格尺度上发生的异常猛烈的网格点风暴。这将通过更好地理解对流与大气环流在小尺度和大尺度上的相互作用，并通过发展一种在数值模式中表示对流的新方法来实现。对流与大气环流的相互作用是极其复杂和鲜为人知的。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：Hadley环流和热带辐合区，Walker环流，以及对流耦合波。我们将通过使用全球环流的简化模型来进行仔细受控的假设检验实验和敏感性测试，从而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。这项模拟工作将通过开发一种新的理论模型来补充，该模型描述了对流与大气边界层和更大尺度环流的相互作用。这个新的理论模型将被用来理解边界层在确定Walker环流结构中的作用。这项工作的第三步将是使用理论和数值模式来了解边界层在影响对流日循环中的作用。全球天气预报模式和气候模式目前分别使用粗于10公里和数量级10‘S公里的网格分辨率。该模式的所谓“动力核心”预测了风场和温度场在这些分辨尺度上的演变。然而，典型的对流云的水平尺度约为1公里。因此，这样的模式不能分解单个对流云。相反，对流是用子网格模型或“参数化”方案来表示的，它试图对对流对分辨率尺度的影响进行建模。这里我们提出了一种新的对流表示方法，其中非对流流体和对流流体的风场和温度场分别由动力核来预测。我们将扩展这个双流体模型的理论理解，我们将在一个三维计算机模型中实施它，我们将在一系列日益复杂的测试中评估它的性能。这种新的对流表示法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.