Evaluation of convective boundary layer height estimates using radars operating at different frequency bands

Abstract. Knowledge of atmospheric boundary layer state and evolution is important for understanding air pollution and low level cloud development, among other things. There are a number of instruments and methods that are currently used to estimate boundary layer height (BLH). However, no single instrument is capable of providing BLH measurements in all weather conditions. We proposed a method to derive a daytime convective BLH using radar observations and investigated the consistency of these retrievals between different radars. We utilized data from three vertically-pointing radars that are available at the measurement station in Southern Finland: the C-band (5 GHz), Ka-band (35 GHz) and W-band (94 GHz). The Ka- or W- band cloud radars are an integral part of cloud profiling stations of pan-European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Our method will be utilized at ACTRIS stations to serve as an additional estimate of the BLH during summer months. During this period, echoes from insects and Bragg scatter are often recorded by radars. To retrieve a BLH, we suggested a mechanism to separate small insects that follow air motion and independently flying insects that works for all analyzed frequency bands. At the lower frequency (the C-band) insect scattering was separated from Bragg scattering using a combination of radar reflectivity factor and linear depolarization ratio. Retrieved values of the BLH from all radars are in a good agreement when compared to the BLH obtained with the co-located lidar and reanalysis dataset. Our method showed some underestimation of the BLH after night-time heavy precipitation yet demonstrated a potential to serve as a reliable method to obtain a BLH during clear-sky days. Additionally, the entrainment zone was observed by the C-band radar above the CBL in a form of a Bragg scatter layer. Aircraft observations of vertical profiles of potential temperature and water vapor mixing ratio, collected in the vicinity of the radar, demonstrated some agreement with the Bragg scatter layer.