Saharan dust contribution to the Caribbean summertime boundary layer – A lidar study during SALTRACE
Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high accurate measurements of the linear depolarization ratio down to about 150–200 m above ground level, the dust volume fraction and the dust mass concentration within the Caribbean boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information of the boundary layer height and the meteorological situation within the boundary layer. We investigate the lidar derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find over all mean values and mean uncertainties of 0.04 ± 0.03 and 0.05 ± 0.04 at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and 26 ± 5 sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the Caribbean boundary layer we find that most values are between 20 and 50 g/m3, and that on most days the dust contribution to total aerosol volume is about 30–40 %. Comparing the dust contribution to the columnintegrated sun-photometer measurements we see a correlation of high dust contribution, high total aerosol optical depth and a corresponding low Angström exponent, and of low dust contribution with low total aerosol optical depth and corresponding high Angström exponent. The relative humidity within the boundary layer was high with values around 80 % on most of the days.