The effect of overlying absorbing aerosol layers on remote sensing retrievals of cloud effective radius and cloud optical depth

Haywood, Jim M.; Osborne, S.; Abel, Steven J.

doi:10.1256/qj.03.100

Cited by 155 publications

(205 citation statements)

References 31 publications

Supporting

Mentioning

190

Contrasting

Order By: Relevance

“…Haywood et al (1,2) evaluated the cloud retrievals in the presence of African dust and smoke aerosol. They found that the MODIS droplet effective radius (using the 0.86-and the 2.1-m channels) is not affected by overlying aerosol.…”

Section: Data Qualitymentioning

confidence: 99%

“…The Southern Tropical Atlantic (30°S-20°S) is dominated by clean maritime air. The region between 20°S and 5°N is a relatively well defined region covered by smoke from biomass burning in Africa (1,2). The Northern Tropical Atlantic (5°N-30°N) is under heavy influx of dust from Africa (3), and the Northern Atlantic (30°N-60°N) is impacted by anthropogenic pollution aerosol from North America and Europe.…”

mentioning

confidence: 99%

See 1 more Smart Citation

The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean

Kaufman

Koren

Remer

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

611

480

View full text Add to dashboard Cite

Clouds developing in a polluted environment tend to have more numerous but smaller droplets. This property may lead to suppression of precipitation and longer cloud lifetime. Absorption of incoming solar radiation by aerosols, however, can reduce the cloud cover. The net aerosol effect on clouds is currently the largest uncertainty in evaluating climate forcing. Using large statistics of 1-km resolution MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data, we study the aerosol effect on shallow water clouds, separately in four regions of the Atlantic Ocean, for June through August 2002: marine aerosol (30°S-20°S), smoke (20°S-5°N), mineral dust (5°N-25°N), and pollution aerosols (30°N-60°N). All four aerosol types affect the cloud droplet size. We also find that the coverage of shallow clouds increases in all of the cases by 0.2-0.4 from clean to polluted, smoky, or dusty conditions. Covariability analysis with meteorological parameters associates most of this change to aerosol, for each of the four regions and 3 months studied. In our opinion, there is low probability that the net aerosol effect can be explained by coincidental, unresolved, changes in meteorological conditions that also accumulate aerosol, or errors in the data, although further in situ measurements and model developments are needed to fully understand the processes. The radiative effect at the top of the atmosphere incurred by the aerosol effect on the shallow clouds and solar radiation is ؊11 ؎ 3 W͞m 2 for the 3 months studied; 2͞3 of it is due to the aerosolinduced cloud changes, and 1͞3 is due to aerosol direct radiative effect.cloud cover ͉ cloud height ͉ indirect effect ͉ radiative forcing ͉ air quality D uring June through August, the Atlantic Ocean is covered by varying concentrations of several aerosol types, each covering a separate latitude belt (see Fig. 1). The Southern Tropical Atlantic (30°S-20°S) is dominated by clean maritime air. The region between 20°S and 5°N is a relatively well defined region covered by smoke from biomass burning in Africa (1, 2). The Northern Tropical Atlantic (5°N-30°N) is under heavy influx of dust from Africa (3), and the Northern Atlantic (30°N-60°N) is impacted by anthropogenic pollution aerosol from North America and Europe. These aerosols absorb and reflect solar radiation to space (4), thereby affecting the regional atmospheric energy balance. Clouds that form in air laden with high aerosol concentrations tend to contain more numerous but smaller droplets that reflect sunlight and cool the Earth (5). The smaller cloud droplets reduce the efficiency of droplet growth by collision coalescence, which at least under some conditions (6) reduce precipitation formation and increase cloud lifetime (7,8). However, there is a second pathway for aerosols to affect clouds: Smoke, pollution, and dust aerosols absorb solar radiation, heat the atmosphere, and reduce evaporation from the surface (9-11). As a result, smoke over the Amazon or pollution aerosol over the Indian Ocean can inhibit cloud...

show abstract

Section: Data Qualitymentioning

confidence: 99%

mentioning

confidence: 99%

The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean

Kaufman

Koren

Remer

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

611

480

View full text Add to dashboard Cite

show abstract

“…The impact mainly depends on the absorption properties of particles and on the albedo of the cloud underneath. Furthermore, aerosols above clouds induce biases in the retrieved cloud properties (Haywood et al, 2004).…”

Section: F Waquet Et Al: Retrieval Of the Eyjafjallajökull Volcanicmentioning

confidence: 99%

Retrieval of the Eyjafjallajökull volcanic aerosol optical and microphysical properties from POLDER/PARASOL measurements

Waquet

Peers²,

Goloub³

et al. 2014

Atmos. Chem. Phys.

View full text Add to dashboard Cite

Abstract. Total and polarized radiances provided by the Polarization and Directionality of Earth Reflectances (POLDER) satellite sensor are used to retrieve the microphysical and optical properties of the volcanic plume observed during the Eyjafjallajökull volcano eruption in 2010, over cloud-free and cloudy ocean scenes. We selected two plume conditions, fresh aerosols near the sources (three cases) and a downwind volcanic plume observed over the North Sea 30 h after its injection into the atmosphere (aged aerosols). In the near-source conditions, the aerosol properties depend on the distance to the plume. Within the near-source plume, aerosols are mainly non-spherical and in the coarse mode with an effective radius equal to 1.75 (±0.25) µm and an Ångström exponent (AE) close to 0.0. Far from the plume, in addition to the coarse mode, there are particles retrieved in the accumulation mode, suggesting a mixture of sulfate aerosols and volcanic dust, resulting in an AE around 0.8. The properties of the aerosols also depend on whether the plume is fresh or aged. For the downwind (aged) plume, if non-spherical coarse particles as well as some fine mode particles are retrieved, the AE is higher, around ∼ 0.4. In addition, rather low values for the real part of the refractive index (RR) were retrieved for the fresh plume (1.38 < RR < 1.48). Single scattering albedo (SSA) values ranging between 0.92 and 0.98 were retrieved over some parts of the near-source plume; despite the low accuracy of our retrievals, the derived SSA values suggest that the ash particles are rather absorbing. To consider the particle shape, a combination of spheroid models was used. Although the employed model enabled accurate modeling of the POLDER signal in the case of non-spherical ash, our approach failed to model the signal over the optically thickest parts of the near-source plume. The most probable reason for this is the presence of ice crystals within the plume. For the aerosol above clouds (AAC) scenes, polarized measurements allowed the retrieval of the optical thickness (OT) and the AE of optically thin volcanic ash. We found that all the cloud parameters retrieved by passive sensors were biased due to the presence of the elevated volcanic plumes. Finally, thermal infrared measurements were used to identify the type of multilayer scene (cirrus clouds or volcanic dust above liquid clouds) and the retrieval method also provided the OT of thin cirrus layers above the clouds near Iceland.

show abstract

“…The use of underlying bright targets such as stratocumulus clouds may offer some ways forward (e.g. Haywood et al, 2004), although the nearzeroÅngström exponent associated with mineral dust and relatively low absorption would likely make smaller, more highly absorbing particles such as biomass-burning aerosols more suitable for such an approach.…”

Section: Future Perspectivesmentioning

confidence: 99%

Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Haywood

Johnson

Osborne

et al. 2011

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

The Geostationary Earth Radiation Budget Intercomparison of Longwave and Shortwave radiation (GERBILS) was an observational field experiment over NorthAfrica during June 2007. The campaign involved 10 flights by the FAAM BAe-146 research aircraft over southwestern parts of the Sahara Desert and coastal stretches of the Atlantic Ocean. Objectives of the GERBILS campaign included characterisation of mineral dust geographic distribution and physical and optical properties, assessment of the impact upon radiation, validation of satellite remote sensing retrievals, and validation of numerical weather prediction model forecasts of aerosol optical depths (AODs) and size distributions. We provide the motivation behind GERBILS and the experimental design and report the progress made in each of the objectives. We show that mineral dust in the region is relatively nonabsorbing (mean single scattering albedo at 550 nm of 0.97) owing to the relatively small fraction of iron oxides present (1-3%), and that detailed spectral radiances are most accurately modelled using irregularly shaped particles. Satellite retrievals over bright desert surfaces are challenging owing to the lack of spectral contrast between the dust and the underlying surface. However, new techniques have been developed which are shown to be in relatively good agreement with AERONET estimates of AOD and with each other. This encouraging result enables relatively robust validation of numerical models which treat the production, transport, and deposition of mineral dust. The dust models themselves are able to represent largescale synoptically driven dust events to a reasonable degree, but some deficiencies remain both in the Sahara and over the Sahelian region, where cold pool outflow from convective cells associated with the intertropical convergence zone can lead to significant dust production.

show abstract

The effect of overlying absorbing aerosol layers on remote sensing retrievals of cloud effective radius and cloud optical depth

Cited by 155 publications

References 31 publications

The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean

The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean

Retrieval of the Eyjafjallajökull volcanic aerosol optical and microphysical properties from POLDER/PARASOL measurements

Motivation, rationale and key results from the GERBILS Saharan dust measurement campaign

Contact Info

Product

Resources

About