Impact of Terrain, Land-sea Boundaries, and Urban Areas on Convective Initiation, Structure, and Evolution over the Northeast United States

尽管强对流在美国东北部不像美国中部那样频繁，但它仍然发生并危及数千万人。美国东北部的强对流通常很难预测，因为许多地形特征都会改变它，比如潜在的地形和陆地/水域边界。例如，强对流可能由阿巴拉契亚山脉以东的背风槽或海风边界在当地触发，然后与纽约市(NYC)等城市地区相互作用，最后可能在遇到相对凉爽的海洋层时在海岸减弱。然而，这种海洋影响可能取决于天气尺度的气流状况，因为海洋层上方的大尺度强迫和不稳定加剧可以维持对流。这项研究的核心目标有三个：(1)发展美国东北海岸、邻近地形特征和城市中心周围对流频率、强度和起始区分布的空间气候学；(2)探索各种对流系统在接近海岸和纽约地区时如何演变；(3)利用WSR-88D和美国国家闪电探测网(CG)11年来的闪电资料，利用中尺度观测和高分辨率数值模拟方法，研究了该地区近海岸附近的锋线和高空对流的物理过程。超过特定阈值的综合闪电计数、反射率、垂直积分水(VIL)和回声顶部将在新英格兰南部4公里的网格上求和。为了了解该地区的对流演变，将使用对流单体跟踪算法。将使用中尺度模拟和海岸附近的观测来探索三维流动、较冷的海表面温度、城市特征和水上摩擦阻力减少对对流演变的影响。学术价值-关于横跨美国东北部的强对流的正式研究相对较少。该项目将提高对新英格兰南部各种对流类型分布与不同大尺度和中尺度流型的关系的了解，以及对流如何在接近海岸时演变。这项研究将使用WSR-88D雷达等数据集来量化分布和三维结构。关于美国东北部强对流的中尺度模式研究还很少，因此这项研究将对模拟这些事件以及与沿海城市环境中对流的启动和演变有关的物理过程提供新的见解。更广泛的影响--东北对流气候学和个例研究将有助于改进对流事件的预测，因为这些结果将为预报员提供一个更好的概念模型，说明在不同的天气条件和物理过程下沿海对流是如何演变的。数值天气预报社区也将受益，因为数值模式将在大量事件中得到验证。这项研究将培养两名中尺度分析和建模的研究生。本项目还为石溪大学S本科生大气科学课程的本科生研究和本科生的暑期研究与体验提供了机会。最后，本研究的成果将被纳入S中尺度动力学高级研究生班。

Although severe convection is not as frequent over the Northeast United States as the central U.S., it still occurs and endangers tens of millions of people. Severe convection is often difficult to forecast across the Northeast U.S., since numerous physiographic features modify it, such as the underlying terrain and land/water boundaries. For example, severe convection may be triggered locally by lee troughs to the east of the Appalachians or by sea breeze boundaries, and then interact with urban areas such as New York City (NYC), and finally may weaken at the coast when encountering the relatively cool marine layer. However, this marine influence may depend on the synoptic scale flow regime, since elevated large-scale forcing and instability above the marine layer can maintain the convection. The core objectives of the study are threefold: (1) To develop spatial climatology of the distribution of convective frequency, intensity, and initiation areas around the Northeast U.S. coast, adjacent terrain features, and urban centers; (2) To explore how the various convective systems evolve as they approach the coast and the NYC region; (3) To investigate the physical processes associated with squall lines and elevated convection approaching the coast using mesoscale observations and high resolution simulations from a few case studies.Eleven years of WSR-88D and the National Lightning Detection Network cloud-to-ground (CG) lightning data will be used to develop a convective climatology of the region. Composite lightning counts, reflectivity, vertically-integrated water (VIL), and echo tops exceeding certain thresholds will be summed on a 4-km grid over southern New England. In order to understand the convective evolution in this region, a convective-cell tracking algorithm will be utilized. Mesoscale simulations and observations near the coast will be used to explore the three dimensional flow, impact of cooler sea surface temperatures, urban characteristics, and decreased frictional drag over water on the convective evolution. Intellectual Merit - There have been relatively few formal research studies on severe convection across the Northeast U.S. The project will improve understanding of the distribution of various convective types across southern New England in relation to different large-scale and mesoscale flow patterns, as well as how convection evolves as it approaches the coast. This study will use datasets, such as WSR-88D radar to quantify the distribution and three-dimensional structures. There have been few mesoscale model studies of severe convection across the Northeast U.S., so this study will add insight into modeling these events and the physical processes associated with convective initiation and evolution in the coastal urban environment. Broader Impacts - The Northeast convective climatology and case studies will help improve forecasting of the convective events, since these results will provide forecasters with a better conceptual model of how convection evolves near the coast for different synoptic conditions and physical processes. The numerical weather prediction community will also benefit, since the numerical model will be verified for a large number of events. This research will train two graduate students in mesoscale analysis and modeling. This project also provides an opportunity for undergraduate research in Stony Brook''s undergraduate atmospheric science curriculum and the summer Research and Experience for Undergraduates. Finally, the results from this study will be incorporated into PI''s upper-level graduate class on mesoscale dynamics.