A new methodology for PBL height estimations based on lidar depolarization measurements: analysis and comparison against MWR and WRF model-based results

Abstract. The automatic and non-supervised detection of the planetary boundary layer height (z_PBL) by means of lidar measurements was widely investigated during the last several years. Despite considerable advances, the experimental detection still presents difficulties such as advected aerosol layers coupled to the planetary boundary layer (PBL) which usually produces an overestimation of the z_PBL. To improve the detection of the z_PBL in these complex atmospheric situations, we present a new algorithm, called POLARIS (PBL height estimation based on lidar depolarisation). POLARIS applies the wavelet covariance transform (WCT) to the range-corrected signal (RCS) and to the perpendicular-to-parallel signal ratio (δ) profiles. Different candidates for z_PBL are chosen and the selection is done based on the WCT applied to the RCS and δ. We use two ChArMEx (Chemistry-Aerosol Mediterranean Experiment) campaigns with lidar and microwave radiometer (MWR) measurements, conducted in 2012 and 2013, for the POLARIS' adjustment and validation. POLARIS improves the z_PBL detection compared to previous methods based on lidar measurements, especially when an aerosol layer is coupled to the PBL. We also compare the z_PBL provided by the Weather Research and Forecasting (WRF) numerical weather prediction (NWP) model with respect to the z_PBL determined with POLARIS and the MWR under Saharan dust events. WRF underestimates the z_PBL during daytime but agrees with the MWR during night-time. The z_PBL provided by WRF shows a better temporal evolution compared to the MWR during daytime than during night-time.