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

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

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.