On the climate forcing consequences of the albedo continuum between cloudy and clear air

Charlson, Robert J.; Ackerman, A. S.; Bender, Frida A.‐M.; Anderson, Theodore L.; Liu, Zhaoyan

doi:10.3402/tellusb.v59i4.17051

Cited by 53 publications

(81 citation statements)

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“…They are also sensitive to the definition of f c (Fig. 2 and Supporting Information), an issue raised in various other works (42). Analyses should therefore always be associated with clear criteria for definition of f c .…”

Section: Discussionmentioning

confidence: 99%

New approaches to quantifying aerosol influence on the cloud radiative effect

Feingold

McComiskey

Yamaguchi

et al. 2016

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

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The topic of cloud radiative forcing associated with the atmospheric aerosol has been the focus of intense scrutiny for decades. The enormity of the problem is reflected in the need to understand aspects such as aerosol composition, optical properties, cloud condensation, and ice nucleation potential, along with the global distribution of these properties, controlled by emissions, transport, transformation, and sinks. Equally daunting is that clouds themselves are complex, turbulent, microphysical entities and, by their very nature, ephemeral and hard to predict. Atmospheric general circulation models represent aerosol−cloud interactions at everincreasing levels of detail, but these models lack the resolution to represent clouds and aerosol−cloud interactions adequately. There is a dearth of observational constraints on aerosol−cloud interactions. We develop a conceptual approach to systematically constrain the aerosol−cloud radiative effect in shallow clouds through a combination of routine process modeling and satellite and surfacebased shortwave radiation measurements. We heed the call to merge Darwinian and Newtonian strategies by balancing microphysical detail with scaling and emergent properties of the aerosol−cloud radiation system.T he climate system, with its couplings between land surface, vegetation, ocean, cryosphere, and atmosphere, is an extraordinarily complex system that is under intensive scrutiny for the purposes of climate analysis and prediction. The atmospheric aerosol and its interaction with clouds is a poorly quantified component of the climate system and is the focus of the current study. The aerosol comprises suspended particles that derive from the oceans, land surface, volcanoes, and anthropogenic activities. The difficulty in quantifying climate forcing by the aerosol emanates partly from the complexity in the aerosol itself, and partly from the fact that its influence on clouds requires detailed understanding of clouds and cloud feedbacks at a range of spatiotemporal scales. Untangling the multiple cloud responses that occur as a result of aerosol perturbations is particularly difficult (1). As one example, consider the influence of the aerosol on clouds and precipitation. Assuming no change in condensed water, the aerosol, by acting as nucleation sites for droplets, might generate smaller droplets, more reflective clouds (2), and reduced precipitation (3). However, through a multitude of complex and contingent pathways, aerosol-perturbed clouds sometimes appear to have similar reflectance because brightening is offset by reductions in cloud water, a fundamental property controlling cloud reflectance. On short timescales (hours), the aerosol tends to reduce precipitation in shallow, liquid-only clouds, but this may be offset over longer periods (multiple days) (4). Deep, mixed-phase convective clouds present even more complex pathways for generation of precipitation, and even more contingencies. The aerosol appears to change the distribution and intensity of surface rain from deep c...

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Section: Discussionmentioning

confidence: 99%

New approaches to quantifying aerosol influence on the cloud radiative effect

Feingold

McComiskey

Yamaguchi

et al. 2016

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

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“…Although the criteria for identification of clear sky in both surface and satellite observations have been rigorously tested and validated, they may cause some uncertainties when cloud fraction/cloud albedo are low and near the clear-cloudy boundary. The clear-cloudy separation is often fuzzy in presence of high aerosol loading and near cloud edges (Charlson et al, 2007;Koren et al, 2007;Tackett and Di Girolamo, 2009;Varnai and Marshak, 2011). The large scatter at low cloud albedo may be related to the clear-sky identification.…”

Section: Other Possible Factorsmentioning

confidence: 99%

Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

Liu

Jensen

et al. 2011

Atmos. Chem. Phys.

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Abstract. This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surface-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fraction, and cloud albedo. The analytical expression is then used to deduce a new approach for inferring cloud albedo from concurrent surfacebased measurements of downwelling surface shortwave radiation and cloud fraction. High-resolution decade-long data on cloud albedos are obtained by use of this surface-based approach over the US Department of Energy's Atmospheric Radiaton Measurement (ARM) Program at the Great Southern Plains (SGP) site. The surface-based cloud albedos are further compared against those derived from the coincident GOES satellite measurements. The three long-term (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) sets of hourly data on shortwave cloud radiative forcing, cloud fraction and cloud albedo collected over the SGP site are analyzed to explore the multiscale (diurnal, annual and inter-annual) variations and covariations. The analytical formulation is useful for diagnosing deficiencies of cloudradiation parameterizations in climate models.

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“…Cloud properties are retrieved from the cloudy pixels and aerosol properties are retrieved from the cloud-free pixels. It has been shown that the apparent "cloud-free" atmosphere within a cloud field, the "twilight zone", has unique optical properties pointing to contributions from undetected clouds and humidified aerosols (Koren et al, 2007;Charlson et al 2007).…”

Section: Introductionmentioning

confidence: 99%

How small is a small cloud?

et al. 2008

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Abstract.The interplay between clouds and aerosols and their contribution to the radiation budget is one of the largest uncertainties of climate change. Most work to date has separated cloudy and cloud-free areas in order to evaluate the individual radiative forcing of aerosols, clouds, and aerosol effects on clouds.Here we examine the size distribution and the optical properties of small, sparse cumulus clouds and the associated optical properties of what is considered a cloud-free atmosphere within the cloud field. We show that any separation between clouds and cloud free atmosphere will incur errors in the calculated radiative forcing.The nature of small cumulus cloud size distributions suggests that at any resolution, a significant fraction of the clouds are missed, and their optical properties are relegated to the apparent cloud-free optical properties. At the same time, the cloudy portion incorporates significant contribution from non-cloudy pixels.We show that the largest contribution to the total cloud reflectance comes from the smallest clouds and that the spatial resolution changes the apparent energy flux of a broken cloudy scene. When changing the resolution from 30 m to 1 km (Landsat to MODIS) the average "cloudfree" reflectance at 1.65 µm increases from 0.0095 to 0.0115 (>20%), the cloud reflectance decreases from 0.13 to 0.066 (∼50%), and the cloud coverage doubles, resulting in an important impact on climate forcing estimations. The apparent aerosol forcing is on the order of 0.5 to 1 Wm −2 per cloud field.

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On the climate forcing consequences of the albedo continuum between cloudy and clear air

Cited by 53 publications

References 0 publications

New approaches to quantifying aerosol influence on the cloud radiative effect

New approaches to quantifying aerosol influence on the cloud radiative effect

Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

How small is a small cloud?

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