The Organization of Tropical Rainfall

热带云系统和降雨有助于推动全球大气环流，将地球表面附近的热量向上传递数公里。这些对流系统可以形成不同大小的群体，从孤立的阵雨和雷暴到赤道波，再到热带气旋，再到麦登-朱利安涛动（MJO）。麦登-朱利安涛动是一种向东传播的天气系统，由跨越数千公里的对流超星团组成，在每周到每月的时间尺度上主导着热带天气的变化。全球数值天气预报和气候模式仍然不能充分模拟这些有组织的风暴群，因此，热带降雨的变异性太少（或不正确）。改善有组织的热带对流的表现，从而提高天气预报的准确性，将大大改善数十亿热带和亚热带地区依赖降雨进行农业生产的人们的生活；更好地预报强风暴和洪水也将挽救无数人的生命，减少财产损失。此外，随着人类活动导致的气候变化，这些过程可能在未来发生变化，因此，提高全球模式模拟有组织对流的能力将有助于更好地预测全球可能的气候变化情景。全球天气和气候模型将地球划分成大约100公里宽的网格。这些盒子太大了，无法直接模拟导致小规模暴雨的运动，而是根据盒子里的平均条件估计总降雨量。由于计算机资源有限，这种简化的雨量估计是必要的，它忽略了孤立阵雨之间的相互作用和区域天气条件。一个令人兴奋的新研究领域是高分辨率理想模型中有组织对流的研究。这些模型具有恒定的海面温度和恒定的阳光，现在可以在几千公里宽的区域上运行，网格盒只有几公里长，允许对流被明确地表示出来。这些模型开始提供对导致对流团自发增长的过程的洞察，这些对流团最终可以发展成一个大的团，占该区域所有降雨的全部。这些过程在广泛的空间尺度上发生作用，这些尺度在全球模式中没有得到充分解决。然而，在理想模式中导致有组织对流的过程仍然没有得到很好的理解，也不知道它们是否对自然界中组织热带对流也很重要。该奖学金将利用大量高分辨率模型运行、预测分析和卫星观测的档案，在理想情况和观测现象之间进行更直接的比较。最终，这项努力有可能改善全球模型，特别是英国气象局统一模型，模拟热带降雨以及全球天气和气候的方式。该奖学金将在雷丁大学气象系进行，该系是世界领先的大气科学中心。与英国气象局的密切联系确保了这项研究将与正在进行的努力互动，以改进统一模式中对流和热带天气和气候的模拟。此外，还将与其他科学家合作，使用不同的模型来解决类似的问题，这将允许探索可能的模型差异。

Tropical cloud systems and rainfall help drive the global circulation of the atmosphere, transferring heat from near the Earth's surface upward for many kilometres. These convective systems can be found in groups of many different sizes, from isolated showers and thunderstorms to equatorial waves to tropical cyclones to the Madden-Julian Oscillation (MJO), an eastward-propagating weather system composed of superclusters of convection several thousand kilometres across which dominates tropical weather variability on weekly to monthly time scales. Global numerical weather forecast and climate models still do not adequately simulate these organized storm clusters and, as a result, have too little (or incorrect) variability of tropical rainfall. Improvement of the representation of organized tropical convection, and therefore the accuracy of weather forecasts, would greatly improve the lives of billions of people who rely on rainfall for agriculture in the tropics and subtropics; better forecasts of strong storms and flooding would also save countless lives and reduce property damage. Furthermore, these processes may change in the future as the climate changes due to human activities, so an improvement of the ability of global models to simulate organized convection will lead to better predictions of possible climate change scenarios over the whole globe. Global weather and climate models divide the Earth into grid boxes about 100 km across. These boxes are too large to directly simulate the motions responsible for small-scale rainstorms, instead estimating total rainfall based on average conditions in the box. This simplified rain estimation, necessary because of limited computer resources, ignores the interaction of isolated rain showers with each other and regional weather conditions. An exciting new research area is the study of organized convection in high-resolution idealized models. These models, with constant sea surface temperatures and constant sunlight, can now be run on domains several thousand kilometres across and with grid boxes of only a few kilometres long, allowing convection to be represented explicitly. These models are beginning to provide insight into processes that lead to spontaneous growth of convective clusters which can ultimately grow to a single large cluster accounting for all of the rainfall in the domain. These processes act over a wide range of spatial scales which are not fully resolved in global models. However, the processes which lead to organized convection in idealized models are still not well understood, and it is not known whether they are also important for organizing tropical convection in nature. This fellowship will exploit a large archive of high-resolution model runs, forecast analyses, and observations from satellites to make more direct comparisons between idealized cases and observed phenomena. Ultimately, this endeavour has the potential to lead to improvements in the way that global models, especially the UK Met Office Unified Model, simulate tropical rainfall and with it global weather and climate. This fellowship will benefit from being undertaken at the Department of Meteorology at the University of Reading, a world-leading centre for atmospheric science. Close ties with the Met Office ensure that this research will be interactive with ongoing efforts to improve the simulation of convection and tropical weather and climate in the Unified Model. In addition, there will be collaborations with other scientists approaching similar problems using different models, which will allow for exploration of possible model differences.