Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements

Wang, Pi-Huan; McCormick, M. P.; Swissler, T. J.; Osborn, M. T.; Fuller, William; Yue, Glenn K.

doi:10.1029/jd094id06p08435

Cited by 75 publications

(45 citation statements)

References 35 publications

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“…For the number size distribution parameters there are less values to compare and larger differences between the data sets. In number density, the uncertainties reported by Bingen et al (2004b) are larger than the OE error estimates, whereas those estimated by Wang et al (1989) are considerably smaller. The 11% reported by Wang et al (1989), however, account only for particles greater than 0.15 µm although the great majority of the retrieved OE sizes are smaller than that (Fig.…”

Section: Discussionmentioning

confidence: 62%

“…8). Similarly, uncertainties in median particle radius estimated by Wang et al (1989) are smaller than those reported by Bingen et al (2004b) and smaller than those achieved through Optimal Estimation, but their error estimates apply only to radii between 0.1 and 0.7 µm. However, although particles smaller than 0.1 µm may contribute little to the total aerosol extinction, their contribution is important to get accurate estimates of the retrieved aerosol properties (Sect.…”

Section: Discussionmentioning

confidence: 71%

“…The total errors are expected to be higher by about 50% due to disregarded systematic (method bias) errors and contributions from particles smaller than 0.1 µm. The methods and the conditions under which these uncertainties were achieved are described in: (1) Wurl (2008), (2) Steele et al (1999), (3) Thomason and Poole (1993), (4) Steele and Turco (1997), (5) Anderson et al (2000), (6) Bingen et al (2004b), (7) Wang et al (1989), and (8) Bauman et al (2003a) et al ascribe their low number densities and overestimated particle sizes to the inability of SAGE II optical measurements to discriminate very thin particles in the Rayleigh limit of scattering. This suggests that the larger OE number densities and smaller OE median radii tend to be more realistic than those presented by Bingen et al (2004b).…”

Section: Discussionmentioning

confidence: 99%

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Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

et al. 2010

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Abstract. Stratospheric aerosol particles under non-volcanic conditions are typically smaller than 0.1 µm. Due to fundamental limitations of the scattering theory in the Rayleigh limit, these tiny particles are hard to measure by satellite instruments. As a consequence, current estimates of global aerosol properties retrieved from spectral aerosol extinction measurements tend to be strongly biased. Aerosol surface area densities, for instance, are observed to be about 40% smaller than those derived from correlative in situ measurements . An accurate knowledge of the global distribution of aerosol properties is, however, essential to better understand and quantify the role they play in atmospheric chemistry, dynamics, radiation and climate.To address this need a new retrieval algorithm was developed, which employs a nonlinear Optimal Estimation (OE) method to iteratively solve for the monomodal size distribution parameters which are statistically most consistent with both the satellite-measured multi-wavelength aerosol extinction data and a priori information. By thus combining spectral extinction measurements (at visible to near infrared wavelengths) with prior knowledge of aerosol properties at background level, even the smallest particles are taken into account which are practically invisible to optical remote sensing instruments.The performance of the OE retrieval algorithm was assessed based on synthetic spectral extinction data generated from both monomodal and small-mode-dominant bimodal sulphuric acid aerosol size distributions. For monomodal background aerosol, the new algorithm was shown to fairly Correspondence to: D. Wurl (daniela wurl@yahoo.de) accurately retrieve the particle sizes and associated integrated properties (surface area and volume densities), even in the presence of large extinction uncertainty. The associated retrieved uncertainties are a good estimate of the true errors. In the case of bimodal background aerosol, where the retrieved (monomodal) size distributions naturally differ from the correct bimodal values, the associated surface area (A) and volume densities (V ) are, nevertheless, fairly accurately retrieved, except at values larger than 1.0 µm 2 cm −3 (A) and 0.05 µm 3 cm −3 (V ), where they tend to underestimate the true bimodal values. Due to the limited information content in the SAGE II spectral extinction measurements this kind of forward model error cannot be avoided here. Nevertheless, the retrieved uncertainties are a good estimate of the true errors in the retrieved integrated properties, except where the surface area density exceeds the 1.0 µm 2 cm −3 threshold.When applied to near-global SAGE II satellite extinction measured in 1999 the retrieved OE surface area and volume densities are observed to be larger by, respectively, 20-50% and 10-40% compared to those estimates obtained by the SAGE II operational retrieval algorithm. An examination of the OE algorithm biases with in situ data indicates that the new OE aerosol property estimates tend to be more realistic tha...

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Section: Discussionmentioning

confidence: 62%

Section: Discussionmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

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Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

et al. 2010

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“…Ångström, 1929;Wang et al, 1989;Bingen et al, 2004). In this paper, we show that the same retrieval technique Bourassa et al (2007) apply at 750 nm can be applied to the limb radiance profile at 1530 nm that is measured by one of the channels of the InfraRed Imaging (IRI) module of OSIRIS.…”

Section: Introductionmentioning

confidence: 96%

Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra

2008

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Abstract.Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with two coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.

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“…Heintzenberg et al [1981] calculated the ratio of the cross sections at different wavelengths as a function of particle radius to determine the region in which useful information could be obtained. This criterion sets effective upper and lower limits in particle radius of 1.0 and 0.1 /am for size discrimination from measurements made by SAGE II [Wang et al, 1989]. A third problem arises from the sensitivity of optical extinction to the moments of the size distribution.…”

Section: Introductionmentioning

confidence: 99%

Retrieval of aerosol size distributions from satellite extinction spectra using constrained linear inversion

Steele¹,

Turco²

1997

J. Geophys. Res.

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Abstract. We examine the retrievability of stratospheric aerosol size distributions from stratospheric aerosol and gas experiment (SAGE) II extinction measurements. Analytical size distributions, which have been fitted to in situ measurements, are used as a model in conjunction with a Mie scattering code to produce synthetic extinction spectra at the SAGE II observational wavelengths. These synthetic data are analyzed using a constrained linear inversion procedure to deduce the variety of particle size distributions which can satisfy them. Fidelity of the retrieval depends on the range of radii over which the inversion is carried out and the range of wavelengths over which measurements are available, but is less sensitive to the number of wavelength channels. As expected, solutions are not unique and depend upon the weighting function used to constrain the solution and the degree of "smoothness" imposed. A given set of extinction measurements may be attributed to either a unimodal or bimodal size distribution, and the selection of a single solution is always subjective to some degree. For bimodal distributions the larger particle mode can be recovered reasonably well; however, the smaller particle mode of a bimodal distribution or the single mode of the background aerosol, which lie below the experiment's sensitivity range, cannot be retrieved accurately. The retrieval of any physically reasonable solution becomes increasingly difficult in the presence of experimental error. In many simulations in which a 10% random error was added to the extinction measurements, only solutions which were strongly influenced by the weighting function could be obtained. Integrated aerosol properties, such as total surface area and volume, can be retrieved to within 25 and 15% for particles in the size range between 0.1 and 1.0/•m from the SAGE II data using this technique. However, these error estimates must be increased to account for particles lying outside this range. It is these latter parameters which are most directly applicable to global chemistry and climate change studies.

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Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements

Cited by 75 publications

References 35 publications

Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra

Retrieval of aerosol size distributions from satellite extinction spectra using constrained linear inversion

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