Dynamics of Interactions between Wave Packets and Explosive Cyclogenesis over Western North Pacific

在凉爽的季节，西北太平洋经常有强气旋。其中一些会爆炸性加深，产生危险的风和巨浪。有迹象表明，与强度较小的风暴相比，这些气旋更难预测。西太平洋气旋给该地区带来了恶劣天气，同时也激发了罗斯比波列车，这些列车迅速向东传播，在几天内影响到美国甚至欧洲。最近的研究表明，西太平洋的分析和预报误差会迅速向下游传播，影响美国的天气预报。该调查员最近的统计分析表明，西太平洋和中太平洋的气旋发展受到亚洲已有的对流层上层波包的强烈影响-在俄罗斯或整个南亚发现具有适当配置的波包三天后，爆炸性气旋发生的频率明显更高。此外，初步模拟研究表明，在这些波包的影响下发生的爆炸性气旋生成可能比在没有波包的情况下发生的爆炸性气旋生成更可预测--在某些情况下，西太平洋爆炸性气旋生成可以在发生前8天进行强有力的预测。这个项目的主要目标是探索和了解高层波包和地面气旋生成之间的相互作用的动力学。此外，还将探讨影响这些事件的可预测性的因素，并研究波包对美国天气的影响。将尽管存在显著的上游动力强迫但没有发生气旋发生的情况与可以强有力地模拟气旋发生的情况进行比较，以了解抑制或有利于快速气旋发生的条件。将采用一套建模和诊断研究。主要的建模工具是NCAR社区大气模式(CAM)。对于每个选定的案例，将使用组合卡尔曼滤波技术进行组合数据同化。这一系列分析将被用作初始条件，以获得一系列预报。有了这个预报集合，就可以评估这些事件的可预测性。基于系综的敏感性分析将揭示影响这些事件演变的重要因素。位涡诊断和反演技术将被用来进行基于特征的敏感性研究，以检查可能对这些事件在中期范围内的演变有重大影响的动力因素。这项研究解决了预报中的一个主要问题--爆炸性气旋发生会产生高度影响的天气，而这些事件往往没有得到很好的预报。通过将事件分成不同的类型，并量化每种类型的可预测性差异，结果可能有助于预报员解释这些事件的模型预测。对这些事件动力学的详细研究将为研究人员提供新的信息，即如何通过澄清非绝热过程、动力学和初始条件中的不确定性所起的不同作用来改进对这些事件的预测。西太平洋气旋经常激发向东传播的Rossby波列，在美国上空产生高影响天气事件，如暴风雪和洪水。这项研究的更广泛影响在于，高影响天气预报的改善可以产生重大的社会效益。

During the cool season, the western North Pacific is frequented by strong cyclones. Some of these deepen explosively to generate dangerous winds and huge waves. There are indications that these cyclones are less predictable than less intense storms. Western Pacific cyclones bring hazardous weather to the region; at the same time, they excite Rossby wave trains that propagate rapidly eastward to affect the U.S. and even Europe within a few days. Recent studies have shown that analysis and forecast errors over the western Pacific propagate quickly downstream to affect weather forecasts for the U.S. Recent statistical analyses by the investigator showed that cyclone development over the western and central Pacific is strongly affected by pre-existing upper-tropospheric wave packets over Asia - the frequency of occurrence of explosive cyclogenesis is significantly higher three days after wave packets having the appropriate configuration are found either over Russia or across southern Asia. Moreover, preliminary modeling studies suggest that explosive cyclogenesis that occurs under the influence of these wave packets may be much more predictable than that which occurs in the absence of wave packets - in some cases, western Pacific explosive cyclogenesis can be robustly forecasted up to eight days before it occurs. The main goal of this project is to explore and to understand the dynamics of the interactions between upper-level wave packets and surface cyclogenesis. In addition, factors affecting the predictability of these events will be explored, and the impacts of wave packets on U.S. weather will be examined. Cases in which cyclogenesis did not occur despite the presence of significant upstream dynamical forcings will be compared to cases in which cyclogenesis can be robustly simulated, in order to understand the conditions that inhibit or favor rapid cyclogenesis. A suite of modeling and diagnostic studies will be employed. The main modeling tool is the NCAR Community Atmospheric Model (CAM). For each selected case, ensemble data assimilation, using the technique of the ensemble Kalman filter, will be conducted using CAM. This ensemble of analyses will be used as initial conditions to obtain an ensemble of forecasts. With this forecast ensemble, the predictability of these events can be assessed. Ensemble-based sensitivity analyses will expose the important factors that affect the evolution of these events. The technique of potential vorticity diagnostics and inversion will be used to conduct feature-based sensitivity study to examine dynamical factors that may have significant impacts on the evolution of these events over the medium range. This study addresses a major issue for forecasting - explosive cyclogenesis generates high impact weather, and frequently these events are not well forecasted. The results may assist forecasters in interpreting model forecasts of these events by stratifying events into different types and quantifying the differences in predictability of each type. Detailed studies of the dynamics of these events will provide researchers with new information about how to improve the prediction of these events by clarifying the different roles played by diabatic processes, dynamics, and uncertainties in initial conditions. Western Pacific cyclones frequently excite Rossby wave trains that propagate eastward to produce high impact weather events, such as blizzards and floods, over the U.S. The broader impact of this study is in the significant societal benefits that can derive from improved forecasts of high impact weather.