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 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 multiwavelength lidars BERTHA (Backscatter Extinction lidar Ratio Temperature Humidity profiling Apparatus) and PO-LIS (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 col-umn (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.

Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

“…For this reason mineral dust particle mi-crophysical properties were updated in the latest OPAC version (v4.0; Gasteiger et al, 2011;Koepke et al, 2015). They are now calculated by means of the T-matrix method (Waterman, 1971) under assumptions of an aspect ratio distribution for prolate spheroids observed during the Saharan mineral dust experiments SAMUM-I and SAMUM-II (Kandler et al, 2009(Kandler et al, , 2011. Several studies have shown that T-matrix theory substantially improves the agreement between measured and modeled aerosol optical properties of aspherical mineral dust particles (Mishchenko et al, 1997;Kahnert et al, 2005;Gasteiger et al, 2011) and are thus motivating its use in this study.…”

Aerosol particle depolarization ratio at 1565 nm measured with a Halo Doppler lidar

“…Over the last few years these lidars have become widely used in wind and turbulence studies (e.g. Päschke et Vakkari et al, 2015;Tuononen et al, 2017;Manninen et al, 2018). Additionally, depolarization ratio measurements by Halo lidars have been used to study cloud and precipitation phase (e.g.…”

Thermal infrared dust optical depth and coarse-mode effective diameter retrieved from collocated MODIS and CALIOP observations

“…As the fine-mode PSD has a negligible impact on dust optical properties 495 in TIR, the result suggests that the AERONET coarse-mode PSD is highly likely to be underestimated in terms of size, which has been pointed out in several studies comparing AERONET PSD with other in-situ measurements (Müller et al, 2010;Müller et al, 2012;Mcconnell et al, 2008;Adebiyi et al, 2023). Due to the difficulties of comparing the PSD from the column-integrated retrieval to that from the lofted-layer measurement (Toledano et al, 2019), the possible reasons are as-of-yet not well-explained, which require detail investigations in the future. 500…”