Sun photometer retrievals of Saharan dust properties over Barbados during SALTRACE

Abstract. The Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) was devoted to the investigation of Saharan dust properties over the Caribbean. The campaign took place in June–July 2013. A wide set of ground-based and airborne aerosol instrumentation was deployed at Barbados island for a comprehensive experiment. Several sun photometers performed measurements during this campaign: two AERONET Cimel sun photometers and the Sun and Sky Automatic Radiometer (SSARA). The sun photometers were co-located with the ground-based multi-wavelength lidars BERTHA and POLIS. Aerosol properties derived from direct sun and sky radiance observations are analyzed, and a comparison with the co-located lidar and in-situ data is provided. The time series of aerosol optical depth allows identifying successive dust events with short periods in between in which the marine background conditions were observed. Moderate aerosol optical depth in the range 0.3 to 0.6 was found during the dust periods. The sun photometer infrared channel at 1640 nm wavelength was used in the retrieval to investigate possible improvements and expected larger sensitivity to coarse particles. The comparison between column (AOD) and surface (dust concentration) data demonstrates the connection between the Saharan Air Layer and the boundary layer in the Caribbean region, as it is shown by the synchronized detection of the successive dust events in both data sets. However the comparison of size distributions derived from sun photometer data and in-situ observations reveal the difficulties to carry out a column closure study.