Year-round urban modifications and urban-plume effects of the mixed-layer height, boundary-layer clouds, and fog revealed by a ceilometer network in Berlin, Germany

Detailed observations of the atmospheric boundary layer (ABL) provide fundamental information to identify and understand potential spatial heterogeneity in urban and rural environments with respect to surface-atmosphere exchanges and resulting ABL characteristics. This is particularly relevant in the context of understanding dynamic feedbacks between cities and the ABL to, e.g., further develop and apply next-generation numerical weather prediction and climate models. During a year-long measurement campaign in Berlin, Germany (urbisphere-Berlin, October 2021-September 2022), a large variety of ABL observations were made within the city and surrounding rural regions. These observations included, as a central component of the campaign, a rigorous and systematic network of 25 sites with ground-based Automatic Lidar and Ceilometers. These instruments collected high-resolution data on aerosol backscatter profiles to enable investigations of intra-urban, urban-rural, and upwind-city-downwind effects of the mixed layer, ABL clouds, and near-surface fog conditions. Our year-round investigation highlights systematic effects along diurnal and annual cycles of the mixed-layer height, being higher above the city and showing intra-urban differentiation. The comprehensive data set further depicts urban modifications of ABL clouds along the diurnal cycle, including urban-plume effects. Moreover, the occurrence of ground-based fog is on average 1,5 times higher in rural regions compared to the city with strongest urban-rural differences during autumn and winter. The high-resolution ceilometer data set, in combination with the multitude of other ABL observations collected during urbisphere-Berlin, will enable and support future studies that focus on, e.g., surface-atmosphere energy exchanges, aerosol effects on radiation fluxes, or validation of urban climate models.