Synoptic Climatology of Factors Contributing to Precipitation Over the Eastern United States

关于降水的大气研究往往侧重于对最严重事件的调查。因此，研究尚未能够确定导致降水的因素（例如，湿脊、喷流条纹和不稳定性）以及这些因素的组合，这些因素有效地区分极端降水事件和普通降水事件。已经确定了大气场与强降水量之间的广义关系，但这些关系通常很弱，并受到其他因素（如地理和天气制度）的强烈调节。此外，这些关系不能解释降水事件的空间特征。本项目将探讨降水的天气气候学，明确关注导致降水的不同因素与不同类型降水事件之间的联系。文献中与降水相关的次天气尺度大气特征将在美国东部三分之二的30个暖季中发生的所有降水事件附近确定。将计算的特征包括脊状特征的强度、存在与否、事件的传播速度和持续时间，以及不同特征之间的位置关系。将进行统计分析，根据相关促成因素的特征和与不同类型降水事件相关的特征组合对降水事件进行分类。通过该项目进行的气候学分析将用于为文献中报道的极端降水事件的案例研究建立气候学背景。该项目将为评估各种亚天气尺度特征在不同类型降水事件中的相对作用提供气候学依据。它将确定极端事件与异常因素或不太可能的因素组合的关联程度。该项目将提供关于大气模式与不同类型降水事件发生之间关系的基本见解，从而有助于加强降水预报以及对与大气动力学有关的广泛其他问题的理解。

Atmospheric research on precipitation tends to focus on the investigation of the heaviest events. As a result, studies have not yet been able to identify those factors that lead to precipitation (e.g., moisture ridging, jet streaks, and instability) as well as combinations of those factors that effectively discriminate extreme precipitation events from ordinary ones. Generalized relationships have been identified between atmospheric fields and heavy precipitation amounts, but these relationships typically are weak and mediated strongly by other factors (e.g. geography and synoptic regimes). Furthermore, these relationships do not account for the spatial characteristics of the precipitation event. This project will explore the synoptic climatology of precipitation, with explicit attention given to links between different factors that lead to precipitation and different types of precipitation events. Sub-synoptic-scale atmospheric features associated with precipitation in the literature will be identified in the vicinity of all precipitation events occurring over 30 warm seasons across the eastern two-thirds of the U.S. Among the features that will be computed are the strength, presence, or absence of ridging features, the propagation speed and persistence of events, and locational relationships among different features. Statistical analyses will be conducted to categorize precipitation events according to the characteristics of the associated contributing factors and to combinations of characteristics associated with different types of precipitation events. The climatological analyses developed through this project will be used to establish a climatological context for case studies of extreme precipitation events reported in the literature. This project will provide a climatological basis for assessing the relative roles of various sub-synoptic-scale features in different types of precipitation events. It will determine the extent to which extreme events are associated with unusual contributing factors or unlikely combinations of factors. This project will provide fundamental insights into relationships between atmospheric patterns and the occurrence of different types of precipitation events, thereby contributing to the enhancement of precipitation forecasting as well as to understandings of a broad range of other issues associated atmospheric dynamics.