T-PARC: Ensemble Simulation and Clustering of the Evolving Cyclone Structure Through Extratropical Transition (ET)

本研究解决了观测系统研究和可预测性实验（THORPEX）太平洋亚洲区域运动（T-PARC）的多个科学目标，包括(i)在风暴向极地移动时提高对北太平洋温带气旋过渡（ET）动力学的认识，（ii）改进集合预报系统的解释和效用，以及（iii）测试高分辨率提供的本地和下游预报技能的改进。它还与THORPEX集成大全球集合(i)开发组合集合的新方法以及（ii）加强在国际上以及业务中心和大学之间开发集合预测方面的合作的目标具有协同作用。热带气旋经历温带转变（ET）时，会经历快速的结构变化，从一个深暖核气旋转变为一个冷核气旋。这提出了一个主要的预测问题和数值模拟挑战。过渡性气旋的混合结构是否得到充分解决以捕捉复杂的过渡过程仍然是一个悬而未决的问题，但PI对两个全球运行模式在模拟ET时间和结构演变方面的预测技能的评估发现，这些运行模式缺乏确定性预测。集合预报系统通过探索初始涡旋和环境结构的不确定性，提供了在ET情况下评估数值制导置信度的潜力。在这个项目中，欧洲中期天气预报中心（ECMWF）对风暴结构的整体预报在气旋相空间（CPS）的框架内进行了评估。气象学和统计学之间的合作将包括：(1)开发基于气旋结构的子系统，用于预测ET的路径和强度；(2)将风暴结构演变的客观划分扩展到基于混合的CPS路径聚类；(3)量化ECMWF集合预报在初始涡结构方面的传播。本研究的智力价值在于创造性地利用新的统计和数值模拟方法，通过热带气旋初始的蒸散发来研究气旋结构演变的强迫因素。本研究的广泛影响包括将新的统计技术应用于天气气象学，并测试天气研究和预报模型配置用于模拟ET的有效性。社会影响包括与ET相关的当地恶劣天气预报的改进潜力，因为这些严重依赖于气旋结构。

This research addresses multiple scientific goals of the THe Observing system Research and Predictability EXperiment (THORPEX) Pacific Asian Regional Campaign (T-PARC) including (i) advancing knowledge of the dynamics governing North Pacific Extratropical cyclone Transitions (ET) as the storms move poleward, (ii) improving the interpretation and utility of ensemble forecast systems, and (iii) testing the improvement in local and downstream forecast skill afforded by high-resolution, non-hydrostatic modeling of ET. It is also synergistic with the goals of the THORPEX Integrated Grand Global Ensemble to (i) develop new methods to combine ensembles, and (ii) enhance collaboration on development of ensemble prediction, internationally and between operational centers and universities. Tropical cyclones undergoing extratropical transition (ET) experience rapid structural changes as they transform from a deep, warm core cyclone to a cold core cyclone. This presents a major forecasting problem and a numerical modeling challenge. It remains an open question whether the hybrid structure of the transitioning cyclone is sufficiently well resolved to capture the complex process of transition, but the PI's assessment of the forecast skill of two global operational models at simulating ET timing and structure evolution finds the deterministic forecasts from these operational models to be lacking. Ensemble prediction systems offer the potential for assessing confidence in numerical guidance during cases of ET by exploring the uncertainties in the initial vortex and environment structures. In this project, European Centre for Medium-Range Weather Forecasting (ECMWF) ensemble forecasts of storm structure are evaluated within the framework of the cyclone phase space (CPS). This collaborative effort between meteorology and statistics will encompass: (1) development of cyclone structure-based sub-ensembles for track and intensity forecasts of ET; (2) extension of the objective partitioning of storm structure evolution to mixture-based clustering of CPS tracks; and (3) quantification of the ECMWF ensemble forecast spread in terms of initial vortex structure. Intellectual merit of the research lies in both the creative exploitation of novel statistical and numerical modeling methods to investigate the factors forcing cyclone structure evolution through the ET of initially tropical cyclones. Broader impacts of this research include the application of novel statistics techniques to synoptic meteorology and testing the effectiveness of the Weather Research and Forecast Model configuration for simulating ET. Societal impacts include the potential for improvements in local severe weather forecasts associated with ET, as these are critically dependent on the cyclone structure.