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Atmospheric lidar measurements were carried out at Elandsfontein measurementstation, on the eastern Highveld approximately 150 km east of Johannesburgin South Africa throughout 2010. The height of the planetary boundary layer(PBL) top was continuously measured using a Raman lidar, PollyXT(POrtabLe Lidar sYstemeXTended). High atmospheric variability together with a largesurface temperature range and significant seasonal changes in precipitationwere observed, which had an impact on the vertical mixing of particulatematter, and hence, on the PBL evolution. The results were compared toradiosondes, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization)space-borne lidar measurements and three atmospheric models that followeddifferent approaches to determine the PBL top height. These models includedtwo weather forecast models operated by ECMWF (European Centre forMedium-range Weather Forecasts) and SAWS (South African Weather Service), andone mesoscale prognostic meteorological and air pollution regulatory modelTAPM (The Air Pollution Model). The ground-based lidar used in this studywas operational for 4935 h during 2010 (49% of the time). The PBLtop height was detected 86% of the total measurement time (42% ofthe total time). Large seasonal and diurnal variations were observed betweenthe different methods utilised. High variation was found when lidarmeasurements were compared to radiosonde measurements. This could bepartially due to the distance between the lidar measurements and theradiosondes, which were 120 km apart. Comparison of lidar measurements tothe models indicated that the ECMWF model agreed the best with mean relativedifference of 15.4%, while the second best correlation was with the SAWSmodel with corresponding difference of 20.1%. TAPM was found to have atendency to underestimate the PBL top height. The wind speeds in the SAWSand TAPM models were strongly underestimated which probably led tounderestimation of the vertical wind and turbulence and thus underestimationof the PBL top height. Comparison between ground-based and satellite lidarshows good agreement with a correlation coefficient of 0.88. On average, thedaily maximum PBL top height in October (spring) and June (winter) was2260 m and 1480 m, respectively. To our knowledge, this study is the first long-term study of PBL top heights and PBL growth rates in South Africa

Atmospheric boundary layer top height in South Africa: measurements with lidar and radiosonde compared to three atmospheric models