Climatology of dust aerosol size distribution and optical properties derived from remotely sensed data in the solar spectrum

Abstract

Abstract. Simultaneous spectral remote observations of dust properties from space and from the ground create a powerful tool for the determination of ambient dust properties integrated on the entire atmospheric column. The two measurement methods have a complementary sensitivity to variety of dust properties. The methodology is demonstrated using spectral measurements (0.47-2.21 p•m) from Landsat TM over the bright Senegalian coast and dark ocean, and Aerosol Robotic Network (AERONET) radiances measured in several locations. We derive (1) the dust size distribution, showing a dominant coarse mode at 1-5 p•m and a secondary mode around 0.5 p•m effective radius; (2) dust absorption, which is found to be substantially smaller than reported from previous measurements; (3) the real part of the refractive index which varies within the range 1.53-1.46; and we show that (4) the effect of the dust nonspherical shape on its optical properties is not significant for scattering angles <120 ø . These Saharan air outbreaks observed during the past decades [e.g., Prospero, 1981;Morales, 1986;Pye, 1987] are covering very large areas with large dust concentrations, so they were suspected to have a significant radiative impact on climate and on remote sensing of the ocean productivity. Table 1. We selected Sal Island (Cap Verde) on the West, Sede Boker (Israel) on the East, for getting the dust properties as it emerges from the two sides of the Sahara. Banizoumbou (Niger), located on the southern edge of the desert, is the station that is more representative of dust properties near the sources. These stations operated at least for several months and the time period is also reported in Table 1 et al., 1988b]. Then, the surface reflectance p is used to calculate the expected apparent reflectance in the dusty day, April 15 1987, using again the ground-based measured optical thickness (optical thickness at 0.64 txm of 2.4). The aerosol properties, i.e., the singlescattering albedo over land and the real part of the refractive index over the ocean, are adjusted to get the best match between the theoretical computations and the TM data. Table 2 the effective radius of the coarse mode only is also reported. It is quite stable and independent of the aerosol content. Let us note that the results for Sede Boker are less TANRE ET AL.: PHYSICAL AND OPTICAL PROPERTIES OF SAHARAN DUST Results General Evolution of the Optical Thickness and

Mie simulations as an error source in mineral aerosol radiative forcing calculations

“…Thus one can hardly claim that the values used in this study are 'representative' for certain situations. However, one can safely state that the lower value of τ = 0.25 lies within the range of typical background values in and near arid regions, whereas the upper value of τ = 1.10 lies within the range of typical dust storm values (d 'Almeida, 1987;Tanré et al, 2001;Holben et al, 2001).…”

Origin and pathways of the mineral dust transport to two Spanish EARLINET sites: Effect on the observed columnar and range-resolved dust optical properties

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Numerical Studies on a Severe Dust Storm in East Asia Using WRF-Chem

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