Details for Wind-driven influences on aerosol light scattering in north-east Atlantic air

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Name:Wind-driven influences on aerosol light scattering in north-east Atlantic air
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Vaishya, A., S. G. Jennings, and C. O Dowd (2012), Wind-driven influences on aerosol light scattering in north-east Atlantic air, Geophys. Res. Lett., 39 , L05805, doi:10.1029/ 2011GL050556.


 

Abstract. Ten years (20012010) of aerosol light-scattering measurements in N.E. Atlantic marine air are analysed to determine wind-speed related influences on scattering properties. The scattering coefficient and the backscattering coefficient dependency on wind speed (U) was determined for the winter (Low Biological Activity-LBA) and the summer seasons (High Biological Activity-HBA), and was found to be dependent on ~ U2. In spite of having a U2 dependency, scattering properties for the LBA-period are approximately twice those of the HBA-period. 96% of the LBA-HBA scattering difference can be explained by the combined effects of size distribution and refractive index differences while 70% of the scattering difference can be attributed to a difference in refractive index alone resulting from organic-matter enrichment during the HBA period. The 550 nm scattering coefficient was ~ 70 Mm-1 for ~ 25 ms-1 wind speeds, which is considerably higher than that encountered under polluted air masses in the same region. Indeed, Mulcahy et al. [2008] reported a high correlation between aerosol optical depth (AOD) and wind-speed with AOD values of 0.30.4 at moderately high wind speed. They found a power-law dependency between wind speed and AOD and suggested that sea spray contributed significantly to the direct radiative effect. O’Dowd et al. [1999] highlighted the preferential activation of sea salt nuclei over sulphate nuclei in marine clouds, while Ovadnevaite et al. [2011] found that even the water insoluble organic sea spray plumes have almost a 100% activation efficiency even at a low supersaturation of 0.2%, pointing to a significant role for sea spray in the direct radiative effect. While there have been many studies of aerosol lightscattering in remote locations and in marine air [Bodhaine, 1996; Parameswaran et al., 1998; Pereira et al., 2011], there have been few studies [e.g., Kleefeld et al., 2002] that have reported wind-dependent scattering dependency. The aim of present study is to establish a wind-speed scattering relationship for clean marine air masses for conditions representative of periods with high organic matter enrichment and periods with low organic matter enrichment.

 

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