Understanding the Consequences of Interactions between Deep Convective Storms and Large Cities

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Large cities can have significant impacts on local weather due to land-use characteristics. The Urban Heat Island is the most well-known consequence of cities, but prior research on precipitation and lightning has provided an indication that cities can also affect the location and strength of thunderstorms. This award provides funding for a numerical modeling study of the potential for urban storm modification with a specific focus on severe weather potential. The intent of the study is to determine which storm processes are most affected by an urban area and which urban features are most likely to modify significant storms. The output from this work will provide operational forecasters with additional information relevant to public safety. The award will also help to train the next generation of scientists through support of students and the development of learning modules for K-12 teachers.This project intends to improve the understanding of interactions between deep convective storms and large urban areas. Most prior research in the area of storm-urban interactions has focused on weakly-forced events and/or the resultant precipitation from those storms, and the community has not coalesced around the dominant mechanism for storm modification (Urban Heat Island (UHI), flow obstruction, aerosols, moisture). This study will consist of a large parameter space study to investigate the cause-and-effect relationship between urban parameters and storm modification. The first step will be a CM1-based set of ~150 idealized sensitivity experiments, with grid sizes 250m. The WRF-ARW would then be used to examine instances of storm modification in real-data cases around Louisville, KY using a 10-member ensemble approach. The UHI will be adjusted by assimilating data from a network of 30 observation sites around the city. Finally, the observational network will be used to analyze the spatial variability in convective rainfall amounts. The overarching questions that the proposal would address are: 1) Which in-storm processes are most strongly affected by an encounter with a large urban area?, 2) What are the consequences of city-storm interactions as they relate to severe weather potential?, 3) How do different urban features impact the modification of deep convective storms?, and 4) What is the effect of environmental wind shear on urban modification?This project is jointly funded by the Physical and Dynamic Meteorology program and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.