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 (delta) profiles. Different candidates for z(PBL) are chosen and the selection is done based on the WCT applied to the RCS and delta. 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.