Sun photometer retrievals of Saharan dust properties over Barbados during SALTRACE

Carlos Toledano,Josef Gasteiger,David Farrel,Benjamín Torres,Silke Groß,Bernadett Weinzierl,David Mateos,Matthias Wiegner,Albert Ansmann,Moritz Haarig,Thomas Müller,Cristian Velasco-Merino,Dietrich Althausen,Victoria E Cachorro,Ramiro González

doi:10.5194/acp-19-14571-2019

Abstract

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 the island of Barbados for a comprehensive experiment. Several sun photometers performed measurements during this campaign: two AERONET (Aerosol Robotic Network) 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 (Backscatter Extinction lidar Ratio Temperature Humidity profiling Apparatus) and POLIS (Portable Lidar System). 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 (AOD) allows identifying successive dust events with short periods in between in which the marine background conditions were observed. The moderate aerosol optical depth in the range of 0.3 to 0.6 was found during the dust periods. The sun photometer infrared channel at the 1640 nm wavelength was used in the retrieval to investigate possible improvements to aerosol size retrievals, and it was expected to have a larger sensitivity to coarse particles. The comparison between column (aerosol optical depth) and surface (dust concentration) data demonstrates the connection between the Saharan Air Layer and the boundary layer in the Caribbean region, as is shown by the synchronized detection of the successive dust events in both datasets. However the differences of size distributions derived from sun photometer data and in situ observations reveal the difficulties in carrying out a column closure study.

Highlights

Mineral dust is a major contributor to natural aerosol particles
The shaded areas in the figure indicate the five successive dust events that were detected during the SALTRACE experiment in Barbados, with a moderate aerosol optical depth (AOD) (500 nm) up to 0.6
We indicate the threshold (AOD = 0.15) for separation between marine and dust aerosol predominance for SALTRACE data

Summary

Introduction

Mineral dust is a major contributor to natural aerosol particles. The Sahara is the main source of natural dust in the Northern Hemisphere (Goudie and Middleton, 2001). Mineral dust has important effects on climate due to its interaction with solar radiation (Liao and Seinfeld, 1998) and its contribution to modifying cloud properties and processes (Tang et al, 2016). It is widely known that dust originating in the Sahara is transported across the Atlantic Ocean to the Caribbean (Prospero and Carlson, 1972; Prospero, 1999). Saharan dust affects vast areas the modification of properties and effects along this transport over the Atlantic Ocean are still not well understood

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Conclusion