Analysis of the Transport of Aerosols over the North Tropical Atlantic Ocean Using Time Series of POLDER/PARASOL Satellite Data

Hélène Fréville,Malik Chami,Marc Mallet

doi:10.3390/rs12050757

Abstract

The time series of total, fine and coarse POLAC/PARASOL aerosol optical depth (AOD) satellite products (2005–2013) processed by the POLAC algorithm are examined to investigate the transport of aerosols over the North Tropical Atlantic Ocean, a region that is characterized by significant dust aerosols events. First, the comparison of satellite observations with ground-based measurements acquired by AERONET ground-based measurements shows a satisfactory consistency for both total AOD and coarse mode AOD (i.e., correlation coefficients of 0.75 and bias ranging from −0.03 to 0.03), thus confirming the robustness and performance of POLAC/PARASOL data to investigate the spatio-temporal variability of the aerosols over the study area. Regarding fine mode aerosol, POLAC/PARASOL data present a lower performance with correlation coefficient ranging from 0.37 to 0.73. Second, the analysis of POLAC/PARASOL aerosol climatology reveals a high contribution of the coarse mode of aerosols ( AOD c between 0.1 and 0.4) at long distance from the African sources, confirming previous studies related to dust transport. The POLAC/PARASOL data were also compared with aerosol data obtained over the North Tropical Atlantic Ocean from MACC and MERRA-2 reanalyses. It is observed that the total AOD is underestimated in both reanalysis with a negative bias reaching −0.2. In summary, our results thus suggest that satellite POLAC/PARASOL observations of fine and coarse modes of aerosols could provide additional constraints useful to improve the quantification of the dust direct radiative forcing on a regional scale but also the biogeochemical processes such as nutrient supply to the surface waters.

Highlights

Composed of fine solid particles or liquid droplets suspended in air, aerosols constitute an important part of the atmosphere
The time series of total, fine and coarse POLAC/PARASOL aerosol optical depth (AOD) satellite products (2005–2013) processed by the POLAC algorithm are examined to investigate the transport of aerosols over the North Tropical Atlantic Ocean, a region that is characterized by significant dust aerosols events
Following the previous works of Harmel and Chami [43,52] about the capacity of polarized signal to significantly improve the aerosol type determination, the present paper focuses on the analysis of the transport of aerosols over the North Tropical Atlantic (NTA) Ocean in clear-sky conditions based on a time series of the total, fine and coarse AOD as derived from the polarized observations of POLDER/PARASOL satellite sensor

Summary

Introduction

Composed of fine solid particles or liquid droplets suspended in air, aerosols constitute an important part of the atmosphere Through their microphysical and optical properties, they interact with solar and terrestrial radiation, alter cloud amount and radiative properties (e.g., [1,2,3,4,5]), fertilize ocean and land, and regulate carbon uptake (e.g., [6,7]) with ensuing impacts on climate (e.g., [8,9,10]). Desert dust represent around 70% of global aerosol mass and 25% of the total aerosol optical depth (AOD) at visible wavelengths (e.g., [16,17]) Their primary source of emission is the Sahara desert of Northern Africa (e.g., [18]). It can be observed all year round, reaching its peak of intensity during summer months (e.g., [6,10,25,27,28,29,30,31,32,33,34,35])

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