A Lagrangian Vertical Coordinate Dynamical Core for Global Atmospheric Modelling

英国气象局的天气预报和气候预测是基于一个复杂的计算机模型，该模型通过数值求解大气动力学和热力学方程。这些方程的求解方法是将地球大气层水平地划分为基于经纬度网格的单元，垂直地划分为若干层或水平。目前的气象局模型及其继任者（目前正在开发中，称为ENDGame）将这些水平定义为地球表面以上的特定高度。另一种方法是使用所谓的拉格朗日垂直水平，根据定义，它会随着流体上下移动。从世界各地的计算机模型实验中有一些证据表明，使用拉格朗日垂直水平可以更好地捕捉空气质量特性以及水分和其他成分的传输，并改善能量收支和其他重要热力学特性（如熵）的表现。反过来，这可能导致更准确的天气预报和更现实的气候模拟和预测。有了这个动机，该项目的目标是开发一个使用拉格朗日垂直水平的ENDGame版本，并仔细评估任何潜在利益的实现程度。拉格朗日垂直水准面的一个缺点是，当它们随着流体移动时，它们最终会倾斜和折叠，直到它们不再能准确地代表大气的状态。这种折叠可能需要几个小时或几天的时间，但在陡峭的山脉或雷暴活动区附近可能会快得多。因此，为了在计算机模式中使用，拉格朗日水平必须定期重新初始化，并将模式风场和热力学场重新映射到重新初始化的水平。拟议工作的一个主要部分将涉及调查重新初始化和重新映射的最佳方式，以便不降低使用拉格朗日水平的好处。该项目的高潮将是使用其基于高度的水平和使用拉格朗日水平的新版本的标准ENDGame模型的传输和保护属性的仔细比较。除了使用不同的垂直水平外，这两个模型将尽可能相似;因此，比较将是对使用拉格朗日水平的好处（或其他好处）的一个明确的测试。以前从未进行过如此清晰的比较。这些结果将为英国气象局和世界各地开发大气计算机模型的其他团体提供有价值的信息。在整个项目中与气象局的密切联系将确保，如果拉格朗日垂直坐标成功，那么它可以很容易地在ENDGame的操作版本中实现。

The weather forecasts and climate predictions produced by the Met Office are based on a sophisticated computer model that numerically solves the equations of atmospheric dynamics and thermodynamics. The equations are solved by dividing the Earth's atmosphere up horizontally into cells based on a latitude-longitude grid and vertically into a number of layers or levels. The current Met Office model, and its successor (currently under development, known as ENDGame), define these levels to be at specified heights above the Earth's surface. An alternative would be to use so-called Lagrangian vertical levels, which, by definition move up and down with the fluid. There is some evidence from experiments with computer models around the world that using Lagrangian vertical levels could better capture air mass properties and the transport of moisture and other constituents, and improve the representation of the budget of energy and other important thermodynamic properties such as entropy. This, in turn, could lead to more accurate weather forecasts and more realistic climate simulations and predictions. With this motivation, the aim of the project is to develop a version of ENDGame that uses Lagrangian vertical levels, and carefully assess the extent to which any of the potential benefits have been realized. One of the disadvantages of Lagrangian vertical levels is that, as they move with the fluid, they eventually tilt and fold until they can no longer represent the state of the atmosphere accurately. This folding can take many hours or days high up in the atmosphere but can be much quicker near steep mountains or areas of thunderstorm activity. Therefore, to be used in a computer model, Lagrangian levels must be periodically re-initialized and the model winds and thermodynamic fields remapped to the re-initialized levels. A major part of the proposed work will involve investigating the best way to re-initialize and remap, so that the benefits of using the Lagrangian levels are not degraded. The culmination of the project will be a careful comparison of the transport and conservation properties of the standard ENDGame model using its height-based levels and the new version using Lagrangian levels. Apart from the different vertical levels used, these two models will be as similar as possible; the comparison will therefore be a clean test of the benefits (or otherwise) of the use of Lagrangian levels. Such a clean comparison has not been carried out before. The results will provide valuable information to the Met Office and to other groups around the world developing computer models of the atmosphere. Close contact with the Met Office throughout this project will ensure that, if the Lagrangian vertical coordinate is successful, then it can be readily implemented in the operational version of ENDGame.