Turbulence in the mixed layer over an urban area: a New York City case study

This study examines the turbulence characteristics of the boundary layer over New York City. Understanding the urban boundary layer characteristics is key to forecasting weather in cities, where most people live. Although extensive research into urban boundary layer (UBL) processes have been carried out in the past decades, majority of these studies focussed on the urban surface layer; our understanding of urban mixed layer characteristics is still incomplete. Here we use Doppler lidar observations from multiple sites in New York City to study turbulent properties in the UBL and their relationship to the heterogeneous urban surface. All three sites were influenced by different levels of urbanization. Our analysis shows vertical stratification in momentum transport during non-neutral stability periods. The analysis over multiple sites reveal a degree of homogeneity in mixed layer characteristics, especially during extreme heat episodes. The spectral analysis show high variability in normalized energy density at different heights.