Revolutionizing Convective Parameterization

热带地区的天气和气候以积云为主。这些云层是由大气中强烈的对流产生的。对流将热量和蒸发从地球表面传递到整个大气层。它是控制热带大气温度和水汽含量随高度变化的主要过程。在全球范围内，积云是降雨量的主要来源，对流是地球大气流动总体格局中的一个重要组成部分。用于全球数值天气预报(NWP)和气候预测的大气计算机模拟，将大气分为典型的水平尺寸分别为20公里和100公里的盒子。这意味着这些模型不能正确地表示对流要素(如雷暴)，因为这些要素通常只有1公里左右的大小。然而，由于对流在大气中起着至关重要的作用，它必须在模型中表现出来。我们必须以某种方式估计每个盒子中将出现什么积云，以及它们对更大尺度大气的集体影响。这就是所谓的积云参数化。大气的计算机模拟对于可靠的气候预测和天气预报是必不可少的。从公众个人到对天气敏感的商业活动、从保险部门到紧急服务到政府关于气候风险的政策，这些机构的产出为各方面的决策提供了极大的信息。对流参数化是一个棘手的问题，也是我们面临的最大的单一不确定性。这是一次严峻而无情的考验，考验我们对对流的基础科学及其在大气中的作用的理解程度。众所周知，现有参数化中的缺陷会转化为天气和气候模式中的严重缺陷。仅举一个例子，在许多模式中，预测的对流降雨太频繁和太少。RevCon之所以被称为RevCon，是因为该项目旨在通过挑战数十年来对流参数化中做出的许多关键假设来实现对流参数化的一场革命。这些假设中的一些是非常有限的，在许多情况下都是已知的较差的近似。我们还相信，它们是不必要的，没有它们可以实现更好的参数化。该项目将确定对流参数化的真正数学结构，通过对对流云系的高分辨率模拟的详细分析，了解并仔细证明这种结构是合理的。这是对国家气象中心/气象局在这一领域的方案的重要贡献，因为它将为方案第二阶段提供必要的起点，为气象局的天气预报和气候模式建立新一代参数。

The weather and climate of the tropics is dominated by cumulus clouds. These clouds are produced by vigorous convection currents within the atmosphere. The convection communicates heat and evaporation from the Earth's surface throughout the atmosphere. It is the main process controlling the change of temperature and moisture content with height in the tropical atmosphere. On the global scale cumulus clouds are responsible for the majority of the rainfall, and convection is a crucial component in the overall pattern of the Earth's atmospheric flows. Computer modelling of the atmosphere, both for global numerical weather prediction (NWP) and for climate projection, divides the atmosphere into boxes with typical horizontal sizes of 20 and 100km respectively. This means that the models are not able to represent convective elements (such as thunderstorms) properly, because these elements are typically only around 1km in size. However, as convection has a crucial role to play in the atmosphere, it must be represented within the models. We have somehow to estimate what cumulus clouds will be present in each of the boxes and what their collective effects will be on the larger-scale atmosphere. This is known as a cumulus parameterization. Computer modelling of the atmosphere is essential for reliable climate projections and weather forecasts. Society benefits enormously from their outputs to inform decision making on all scales from the individual member of the public to weather-sensitive business activities to the insurance sector to the emergency services to government policy on climate risks. Convection parameterization is a stubborn and difficult problem and the largest single uncertainty that we face. It is a severe and unforgiving test of just how well we understand the fundamental science of convection and its role in the atmosphere. Defects in the existing parameterizations are known to translate into serious deficiencies in weather and climate models. To give just one example, in many models the predicted convective rainfall is too frequent and too light.RevCon is so named because the project aims at a revolution in convective parameterization by challenging many of the key assumptions that have been made within convective parameterizations for decades. Some of these assumptions are very limiting and known to be poor approximations in many circumstances. We are also convinced that they are unnecessary and that better parameterizations can be achieved without them. This project will establish what the mathematical structure of convection parameterization really should be, with that structure being informed and carefully justified through the detailed analysis of very high-resolution simulations of convective cloud systems. It is a critical contribution to a NERC / Met Office programme in this area because it will provide a necessary starting point for Phase 2 of the programme to build a new-generation parameterization for the Met Office weather forecast and climate model.