Thermal Structure of the Urban Boundary Layer during a Heat Wave Period

This research focused on understanding the impact of heatwaves on the urban boundary layer. Few studies have focused on the thermal structure and evolution of urban boundary layer and even fewer on the impacts of heatwaves. The study used microwave profilers to sense the boundary layer over New York City during July 2016. A period, which witnessed 3 heatwave episodes and heatwave warnings were issued on 16 days. Our analysis shows that the boundary layer, particularly the lower 2 km was highly energized during the heatwave event with the average virtual potential temperature at least 7-10 K higher throughout the boundary layer. Subsidence of warm air from the atmosphere aloft was captured by the profiler. The lower surface layer remained warm for extended periods of time and a heat dome was visible in the lower 250 m. We also found the effects of thermal internal boundary layers, wherein a low level inversion set in. This was mainly a result of local surface characteristics. The strength of this inversion grew during the heatwave episode.   Finally, the nocturnal boundary layer during the heatwave episode remained mostly unstable. Overall the analysis has shown that urban areas can experience elevated temperatures during heatwaves episodes due to complex interactions between the surface and the atmosphere.