Collaborative Research: Environmental Control of Tropical Cyclone Activity

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。最近的研究已经确定，海洋盆地上热带气旋活动的年际到年代际变化的大部分可能是由风暴发展的大尺度大气和海洋环境控制的。大西洋热带气旋活动的统计和基于模式的预报捕获了热带气旋频率年际变化的65%，尽管很少或根本没有考虑潜在的初始扰动，如非洲东风波。然而，这些相同的技术在应用于全球变暖情景时产生了截然不同的结果。这突出表明需要对热带气旋和气候之间的联系有更好的物理认识。本项目将使用几种不同但互补的方法来寻求这样的理解。第一个是利用云尺度模型，研究在辐射-对流平衡与切变的大尺度环境中，由种子气旋扰动形成或不形成热带气旋。该方法的先前结果将扩展到更大范围的风廓线，包括速度和方向切变，允许在现实环境中仔细研究旋风形成（或失败），仍然可以系统地调整和比较。第二种方法建立在创世纪潜力指数（GPI）的成功基础上，当将其应用于历史数据时，已被证明可以解释热带气旋活动的年际变化和长期趋势。在这里，它将被用来理解在模拟全球变暖响应的气候模式中导致GPI预测变化的物理因素。利用云分辨模式模拟的结果，该指数将得到改进。最后，将对云分解模式中的一两个成因进行深入分析，试图验证热带气旋只能在对流层大部分接近饱和的中尺度斑块中发展的假设。更广泛的影响是促进对热带气候和热带气旋活动之间关系的理解。这可能导致对热带气旋活动如何随气候变化而变化的更好和更有用的评估。这项工作也可能使我们对热带气旋的形成过程有更基本的了解，最终对热带低气压和风暴的形成作出更好的短期预报。该项目将支持培训一名年轻科学家或博士后和一名研究生，并将有助于在广泛使用的天气研究与预报（WRF）模式基础上进一步开发灵活的理想飓风建模系统。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Recent research has established that much and perhaps most of the interannual to interdecadal variation of tropical cyclone activity integrated over ocean basins is controlled by the large-scale atmospheric and oceanic environment in which the storms develop. Statistical and model-based hindcasts of Atlantic tropical cyclone activity capture as much as 65% of the interannual variance of tropical cyclone frequency, despite taking little or no account of potential initiating disturbances, such as African easterly waves. These same techniques, however, produce greatly divergent results when applied to global warming scenarios. This highlights the need for a better physical understanding of the link between tropical cyclones and climate. This project will seek such an understanding using several different, but complementary, approaches. The first is an investigation, using a cloud-scale model, of the formation, or failure to form, of tropical cyclones from seed cyclonic disturbances in large-scale environments of radiative-convective equilibrium with shear. Previous results with this method will be extended to a wider range of wind profiles that include speed and directional shear, allowing for a careful study of cyclogenesis (or failure) in realistic environments that still can be systematically adjusted and compared. A second approach builds on the success of the Genesis Potential Index (GPI), which, when applied to historical data, has been shown to explain much of the interannual variance and long-term trend in tropical cyclone activity. Here it will be used to understand the physical factors responsible for predicted variations in the GPI in climate models simulating the response to global warming. The index will be improved using results from the cloud-resolving model simulations. Finally, one or two cases of genesis in the cloud-resolving model will be analyzed in some depth, in an attempt to test the hypothesis that tropical cyclones can develop only in mesoscale patches that are nearly saturated through most of the troposphere.Broader impacts are in advancing understanding of the relationships between tropical climate and tropical cyclone activity. This could lead to better and more useful assessments of how tropical cyclone activity may or may not change with a changing climate. This work may also yield a more fundamental understanding of the process of tropical cyclone formation, ultimately leading to better short-term forecasts of the formation of tropical depressions and storms. The project will support the training of a young scientist or post-doc and a graduate student and will contribute to further development of a flexible idealized hurricane modeling system based on the widely-used Weather Research and Forecasting (WRF) model.