PBL height estimation based on lidar depolarisation measurements (POLARIS)

Abstract

Abstract. The automatic and non-supervised detection of the planetary boundary layer height (zPBL) by means of lidar measurements was widely investigated during the last years. Despite the considerable advances achieved the experimental detection still present difficulties either because the PBL is stratified (typically, during night-time) either because advected aerosol layers are coupled to the PBL. The coupling uses to produce an overestimation of the zPBL. To improve the detection even 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 and to the perpendicular-to-parallel signal ratio (δ) profiles. Different candidates for zPBL are chosen and the attribution is done, based on the WCT applied to the RCS and the δ. We use two ChArMEx campaigns with lidar and microwave radiometer (MWR), conducted on 2012 and 2013, for the POLARIS' adjustment and validation. POLARIS improves the zPBL detection thanks to the consideration of the relative changes in the depolarization capabilities of the aerosol particles in the lower part of the atmospheric column. Taking the advantage of a proper determination of the zPBL determined by POLARIS and by MWR under Saharan dust events, we compare the POLARIS and MWR zPBL with the zPBL provided by the Weather Research and Forecasting (WRF) numerical weather prediction model. WRF underestimates the zPBL during daytime but agrees with the MWR during night-time. The zPBL provided by WRF showed a better temporal evolution during daytime than during night-time.