Retrieval of the aerosol direct radiative effect over clouds from spaceborne spectrometry

Graaf, M. de; Tilstra, L. G.; Wang, P.; Stammes, P.

doi:10.1029/2011jd017160

Cited by 79 publications

(85 citation statements)

References 89 publications

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“…In the case of clean sky condition (i.e., without aerosols), the total radiances scattered by cloud water droplets are relatively spectrally independent from the UV to the shortwave infrared (SWIR) part of the spectrum (De Graaf et al, 2012). At the same time, those wavelengths are sensitive to aerosol effects (i.e., absorption and scattering) whose spectral behaviors depend strongly on the microphysics of the particles (e.g., size, chemical composition, shape).…”

Section: Descriptionmentioning

confidence: 99%

“…Consequently, the presence of an above-cloud aerosol layer affects the signal that can be measured by satellite instruments: the spectral tendency of aerosol absorption leads to a modification of the apparent color of the clouds. Simulations of the upwelling radiance at 490 and 865 nm for ACA events have been processed with a radiative transfer code based on the adding- doubling method (De Haan et al, 1987). In the same way as Fig.…”

Section: Descriptionmentioning

confidence: 99%

“…However, most of the ACAOT retrievals presented above do not evaluate the aerosol single scattering albedo. In contrast, the DRE of aerosols above clouds can also be evaluated without making assumptions about aerosol microphysics thanks to the algorithm developed by De Graaf et al (2012) for Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) measurements. Hyperspectral reflectance from polluted cloud conditions is converted into flux and subtracted from clean cloud conditions.…”

Section: Introductionmentioning

confidence: 99%

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Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

et al. 2015

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Abstract. This study presents an original method to evaluate key parameters for the estimation of the direct radiative effect (DRE) of aerosol above clouds: the absorption of the the cloud albedo. It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER -Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate scattering aerosol optical thickness and aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and cloud optical thickness. The retrieval of aerosol and clouds properties (i.e., aerosol and cloud optical thickness, aerosol single scattering albedo and Ångström exponent) is restricted to homogeneous and optically thick clouds (cloud optical thickness larger than 3). In addition, a procedure has been developed to process the shortwave DRE of aerosols above clouds. Three case studies have been selected: a case of absorbing biomass burning aerosols above clouds over the southeast Atlantic Ocean, a Siberian biomass burning event and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies, both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. The mean DRE is found to be 33.5 W m −2 (warming). Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not greatly the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

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Section: Descriptionmentioning

confidence: 99%

Section: Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

et al. 2015

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“…the cloud albedo), which causes a local positive radiative forcing that contributes to locally warming the atmosphere. Regional studies of the AAC radiative forcing has been achieved (Chand et al, 2009;Peters et al, 2011;De Graaf et al, 2012). However, this forcing is currently not constrained at a global scale, which explains why the estimation of the direct effect of biomass-burning aerosols currently remains poorly estimated (Forster et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Retrieval of aerosol microphysical and optical properties above liquid clouds from POLDER/PARASOL polarization measurements

et al. 2013

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Most of the current aerosol retrievals from passive sensors are restricted to cloud-free scenes, which strongly reduces our ability to monitor the aerosol properties at a global scale and to estimate their radiative forcing. The presence of aerosol above clouds (AAC) affects the polarized light reflected by the cloud layer, as shown by the spaceborne measurements provided by the POlarization and Directionality of Earth Reflectances (POLDER) instrument on the PARASOL satellite. In a previous work, a first retrieval method was developed for AAC scenes and evaluated for biomass-burning aerosols transported over stratocumulus clouds. The method was restricted to the use of observations acquired at forward scattering angles (90–120°) where polarized measurements are highly sensitive to fine-mode particle scattering. Non-spherical particles in the coarse mode, such as mineral dust particles, do not much polarize light and cannot be handled with this method. In this paper, we present new developments that allow retrieving also the properties of mineral dust particles above clouds. These particles do not much polarize light but strongly reduce the polarized cloud bow generated by the liquid cloud layer beneath and observed for scattering angles around 140°. The spectral attenuation can be used to qualitatively identify the nature of the particles (i.e. accumulation mode versus coarse mode, i.e. mineral dust particles versus biomass-burning aerosols), whereas the magnitude of the attenuation is related to the optical thickness of the aerosol layer. We also use the polarized measurements acquired in the cloud bow to improve the retrieval of both the biomass-burning aerosol properties and the cloud microphysical properties. We provide accurate polarized radiance calculations for AAC scenes and evaluate the contribution of the POLDER polarization measurements for the simultaneous retrieval of the aerosol and cloud properties. We investigate various scenes with mineral dust particles and biomass-burning aerosols above clouds. For clouds, our results confirm that the droplet size distribution is narrow in high-latitude ocean regions and that the droplet effective radii retrieved from both polarization measurements and from total radiance measurements are generally close for AAC scenes (departures smaller than 2 μm). We found that the magnitude of the primary cloud bow cannot be accurately estimated with a plane parallel transfer radiative code. The errors for the modeling of the polarized cloud bow are between 4 and 8% for homogenous cloudy scenes, as shown by a 3-D radiative transfer code. These effects only weakly impact the retrieval of the Aerosol Optical Thickness (AOT) performed with a mineral dust particle model for which the microphysical properties are entirely known (relative error smaller than 6%). We show that the POLDER polarization measurements allow retrieving the AOT, the fine-mode particle size, the Ångström exponent and the fraction of spherical particles. However, the complex refractive index and the coarse-...

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“…Cloud droplet number concentrations (CDNC) can also be computed from the aerosol distributions and used in the calculation of cloud optical properties, thus representing the first indirect effect. Representation of the second indirect effect in large-scale climate models has been attempted by parameterising precipitation formation as simple functions of the CDNC, although the value of this method is debated (Stevens and Feingold, 2009), with evidence of climate models overpredicting the strength of the second indirect effect (Quaas et al, 2009;Wang et al, 2012). Since second indirect effects involve adjustments of cloud distributions that are not explicitly represented in the datasets used, this study focuses on the first aerosol indirect effect only.…”

Section: Introductionmentioning

confidence: 99%

Estimates of aerosol radiative forcing from the MACC re-analysis

et al. 2013

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The European Centre for Medium-range Weather Forecast (ECMWF) provides an aerosol re-analysis starting from year 2003 for the Monitoring Atmospheric Composition and Climate (MACC) project. The re-analysis assimilates total aerosol optical depth retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) to correct for model departures from observed aerosols. The re-analysis therefore combines satellite retrievals with the full spatial coverage of a numerical model. Re-analysed products are used here to estimate the shortwave direct and first indirect radiative forcing of anthropogenic aerosols over the period 2003–2010, using methods previously applied to satellite retrievals of aerosols and clouds. The best estimate of globally-averaged, all-sky direct radiative forcing is −0.7 ± 0.3 Wm−2. The standard deviation is obtained by a Monte-Carlo analysis of uncertainties, which accounts for uncertainties in the aerosol anthropogenic fraction, aerosol absorption, and cloudy-sky effects. Further accounting for differences between the present-day natural and pre-industrial aerosols provides a direct radiative forcing estimate of −0.4 ± 0.3 Wm−2. The best estimate of globally-averaged, all-sky first indirect radiative forcing is −0.6 ± 0.4 Wm−2. Its standard deviation accounts for uncertainties in the aerosol anthropogenic fraction, and in cloud albedo and cloud droplet number concentration susceptibilities to aerosol changes. The distribution of first indirect radiative forcing is asymmetric and is bounded by −0.1 and −2.0 Wm−2. In order to decrease uncertainty ranges, better observational constraints on aerosol absorption and sensitivity of cloud droplet number concentrations to aerosol changes are required

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Retrieval of the aerosol direct radiative effect over clouds from spaceborne spectrometry

Cited by 79 publications

References 89 publications

Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

Retrieval of aerosol microphysical and optical properties above liquid clouds from POLDER/PARASOL polarization measurements

Estimates of aerosol radiative forcing from the MACC re-analysis

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