An aerosol model and aerosol‐induced changes in the clear‐sky albedo off the east coast of the United States

Hartley, W. Seth

doi:10.1029/2001jd900025

Cited by 15 publications

(17 citation statements)

References 25 publications

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“…Since the atmosphere was typically more humid than the reference conditions (RH < 40%) measured by the low-humidity AOS nephelometer, this shows that composition, in particular as it affects aerosol hygroscopic growth, can play an important role in determining the asymmetry parameter of atmospheric aerosol. This is consistent with Hartley and Hobbs [2001] and d' Almeida et al [1991] observations that higher humidity conditions lead to higher asymmetry parameter values.…”

Section: Comparison Of Surface Measurement-derived Asymmetry Parameterssupporting

confidence: 93%

“…The range of median g values at ambient conditions found during the IOP (0.60 < g < 0.72) are in the range of values for g reported for other experimental studies. Hartley and Hobbs [2001] reported a median value of 0.7 for aerosol measured during the TARFOX campaign off the East Coast of the United States, while Eck et al [2001] found the same value for polluted aerosol observed during the Indian Ocean Experiment (INDOEX). Formenti et al [2000] found slightly higher values (0.72–0.73) for Saharan dust aerosol.…”

Section: Resultsmentioning

confidence: 71%

“…At ambient humidities, the change in refractive index and particle size due to water uptake can be significant and will influence the calculated optical properties. Hartley and Hobbs [2001], for example, show the strong influence of RH on g , where g increases with RH.…”

Section: Methodsmentioning

confidence: 98%

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Comparison of methods for deriving aerosol asymmetry parameter

Andrews¹,

Sheridan²,

Fiebig³

et al. 2006

J. Geophys. Res.

263

226

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[1] Values for Mie-equivalent aerosol asymmetry parameter (g) were derived using a variety of methods from the large suite of measurements (in situ and remote from surface and aircraft) made in Oklahoma during the 2003 aerosol Intensive Operations Period (IOP). Median values derived for dry asymmetry parameter at 550 nm ranged between 0.55 and 0.63 over all instruments and for all derivation methods, with the exception of one instrument which did not measure over the full size range of optically important aerosol. Median values for the ''wet'' asymmetry parameter (i.e., asymmetry parameter at humidity conditions closer to ambient) were between 0.59 and 0.72. Values for g derived for surface and airborne in situ measurements were highly correlated, but in situ and remote sensing measurements both at the surface and aloft did not agree as well because of vertical inhomogeneity of the aerosol. Radiative forcing calculations suggest that a 10% decrease in g would result in a 19% reduction in top of atmosphere radiative forcing for the conditions observed during the IOP. Comparison of the different methods for deriving g suggests that in computing the asymmetry parameter, aerosol size is the most important parameter to measure; composition is less important except for how it influences the hygroscopic growth (i.e., size) of particles.

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Section: Comparison Of Surface Measurement-derived Asymmetry Parameterssupporting

confidence: 93%

Section: Resultsmentioning

confidence: 71%

See 1 more Smart Citation

Comparison of methods for deriving aerosol asymmetry parameter

Andrews¹,

Sheridan²,

Fiebig³

et al. 2006

J. Geophys. Res.

263

226

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“…The nephelometer integrated over scattering angles from ∼7° to 170° for the total scattering coefficient, and from ∼90° to 170° for the hemispheric backscatter coefficient. Corrections for forward and backward angular truncation and for the nonisotropic light source were applied to the nephelometer measurements, using the methods described by Hartley et al [2000] and Hartley and Hobbs [2001].…”

Section: Methods Of Measurementsmentioning

confidence: 99%

Effects of humidity on aerosols in southern Africa during the biomass burning season

2003

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[1] Measurements of the aerosol total light scattering coefficient, s sp , and the aerosol hemispheric backscatter ratio, b(1), as functions of relative humidity (RH in %) (socalled humidographs) at three wavelengths (450, 550, and 700 nm) were obtained in the dry season in southern Africa (1) in ambient air in South Africa, Botswana, Mozambique and Zambia, (2) at various distances downwind in identifiable smoke plumes from biomass fires, and (3) along the southwest coast of Africa. The ratio of s sp at an RH of 80% to that at 30% provides a measure of the effects of RH on s sp , and similarly for b(1). For the three broad sampling categories given above, and at a wavelength of 550 nm, these ratios varied from 1.42 ± 0.05 to 2.07 ± 0.03 for s sp , and from 0.69 ± 0.05 to 0.99 ± 0.14 for b(1). In general, humidographs for the ambient air samples showed a greater dependence on RH than those for smoke from identifiable biomass fires. During a period when dense, aged smoke was transported to the region from the north, the humidographs for s sp for ambient air samples were similar to those for identifiable smoke plume samples just $10-to 50-min old. This suggests that as far as the effects of RH on s sp are concerned the effects of aging of smoke and its mixing with ambient air are realized within less than about an hour.

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“…The wavelength‐dependent (subscript “ λ ” notation) extinction ( σ ext, λ ), scattering ( σ sca, λ ), and absorption ( σ abs, λ ) coefficients are basic properties of an aerosol that have a good history of measurements and are all dependent on the aerosol number concentration (N a ). Values of σ ext, λ can be determined by adding σ sca, λ and σ abs, λ , and the wavelength‐dependent aerosol optical depth ( τ λ ) can be calculated by integrating σ ext, λ over specific vertical limits [e.g., Hartley and Hobbs , 2001; Magi et al , 2003]. Properties that are not dependent on N a are the wavelength‐dependent single scattering albedo ( ω o, λ = σ sca, λ / σ ext, λ ), backscatter ratio ( β λ ), and asymmetry parameter (g λ ).…”

Section: Introductionmentioning

confidence: 99%

Using aircraft measurements to estimate the magnitude and uncertainty of the shortwave direct radiative forcing of southern African biomass burning aerosol

Magi

Redemann

et al. 2008

J. Geophys. Res.

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[1] We estimate the shortwave, diurnally averaged direct radiative forcing (RF) in cloud-free conditions of the biomass burning aerosol characterized by measurements made from the University of Washington (UW) research aircraft during the Southern African Regional Science Initiative in August and September 2000 (SAFARI-2000). We describe the methodology used to arrive at the best estimates of the measurement-based RF and discuss the confidence intervals of the estimates of RF that arise from uncertainties in measurements and assumptions necessary to describe the aerosol optical properties. We apply the methodology to the UW aircraft vertical profiles and estimate that the top of the atmosphere RF (RF toa ) ranges from À1.5 ± 3.2 to À14.4 ± 3.5 W m À2, while the surface RF (RF sfc ) ranges from À10.5 ± 2.4 to À81.3 ± 7.5 W m À2 . These estimates imply that the aerosol RF of the atmosphere (RF atm ) ranges from 5.0 ± 2.3 to 73.3 ± 11.0 W m À2 . We compare some of our estimates to RF estimated using Aerosol Robotic Network (AERONET) aerosol optical properties and show that the agreement is good for RF toa , but poor for RF sfc . We also show that linear models accurately describe the relationship of RF with the aerosol optical depth at a wavelength of 550 nm (t 550 ). This relationship is known as the radiative forcing efficiency (RFE) and we find that RF toa (unlike RF atm and RF sfc ) depends not only on variations in t 550 , but that the linear model itself is dependent on the magnitude of t 550 . We then apply the models for RFE to daily t 550 derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite to estimate the RF over southern Africa from March 2000 to December 2006. Using the combination of UW and MODIS data, we find that the annual RF toa , RF atm , and RF sfc over the region is À4.7 ± 2.7 W m À2 , 11.4 ± 5.7 W m À2 , and À18.3 ± 5.8 W m À2 , respectively.Citation: Magi, B. I., Q. Fu, J. Redemann, and B. Schmid (2008), Using aircraft measurements to estimate the magnitude and uncertainty of the shortwave direct radiative forcing of southern African biomass burning aerosol,

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An aerosol model and aerosol‐induced changes in the clear‐sky albedo off the east coast of the United States

Cited by 15 publications

References 25 publications

Comparison of methods for deriving aerosol asymmetry parameter

Comparison of methods for deriving aerosol asymmetry parameter

Effects of humidity on aerosols in southern Africa during the biomass burning season

Using aircraft measurements to estimate the magnitude and uncertainty of the shortwave direct radiative forcing of southern African biomass burning aerosol

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