Urban boundary layer structure dynamics derived from remote sensing profile measurements in Zurich, Switzerland

Accurate estimates of atmospheric boundary layer (BL) height, structure, as well as dynamics, are in important ingredient of numerical model evaluation processes. The BL structure and height are essential physical drivers for transport processes in horizontal and vertical directions, with direct implications for air-quality, climate action management assessments like source attribution and concentration thresholds. Between summer 2022 and spring 2023 we conducted an observational campaign in Zurich, Switzerland as part of the ICOS-Cities project (Pilot Applications in Urban Landscapes - Towards integrated city observatories for greenhouse gases). In this study we demonstrate the dynamics of BL height by utilizing vertical profile measurements from a pulsed Doppler Wind Lidar system as well as radiometric temperature measurements. We computed diagnostics on low-level jets, temperature inversion heights, shear layers, turbulent layers and aerosol gradients. Additionally, we used a continuous-wave Doppler Wind Lidar system to obtain data within the urban canopy layer and compared it to wind measurements obtained from co-located sonic anemometry at 100 meters above ground level. We found good agreement between the different measurement systems in general, with certain sectors being directly affected by building wake effects. We use this data to demonstrate the complexity of real-world meteorology in urban, orographically influenced environments and discuss, how the methodology of estimating BL properties affects the results obtained, highlighting opportunities and limitations of remote sensing systems in urban environments.