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

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

doi:10.1111/j.1600-0889.2007.00297.x

Cited by 123 publications

(83 citation statements)

References 46 publications

(64 reference statements)

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“…However, the fact that the ocean 3 km product also does not contain this high bias prompts us towards considering surface effects and not clouds, but without further analysis we cannot make firm conclusions. Future work will definitely need to address cloud 3-D effects (Wen et al, 2007;Marshak et al, 2008), the so-called twilight zone or continuum (Koren et al, 2007;Charlson et al, 2007), and other cloud issues on the finer resolution aerosol product.…”

Section: Discussionmentioning

confidence: 99%

MODIS 3 km aerosol product: algorithm and global perspective

et al. 2013

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After more than a decade of producing a nominal 10 km aerosol product based on the dark target method, the MODerate resolution Imaging Spectroradiometer (MODIS) aerosol team will be releasing a nominal 3 km product as part of their Collection 6 release. The new product differs from the original 10 km product only in the manner in which reflectance pixels are ingested, organized and selected by the aerosol algorithm. Overall, the 3 km product closely mirrors the 10 km product. However, the finer resolution product is able to retrieve over the ocean closer to islands and coastlines, and is better able to resolve fine aerosol features such as smoke plumes over both ocean and land. In some situations, it provides retrievals over entire regions that the 10 km product barely samples. In situations traditionally difficult for the dark target algorithm such as over bright or urban surfaces, the 3 km product introduces isolated spikes of artificially high aerosol optical depth (AOD) that the 10 km algorithm avoids. Over land, globally, the 3 km product appears to be 0.01 to 0.02 higher than the 10 km product, while over ocean, the 3 km algorithm is retrieving a proportionally greater number of very low aerosol loading situations. Based on collocations with ground-based observations for only six months, expected errors associated with the 3 km land product are determined to be greater than that of the 10 km product: ± 0.05 ± 0.20 AOD. Over ocean, the suggestion is for expected errors to be the same as the 10 km product: ± 0.03 ± 0.05 AOD, but slightly less accurate in the coastal zone. The advantage of the product is on the local scale, which will require continued evaluation not addressed here. Nevertheless, the new 3 km product is expected to provide important information complementary to existing satellite-derived products and become an important tool for the aerosol community

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Section: Discussionmentioning

confidence: 99%

MODIS 3 km aerosol product: algorithm and global perspective

et al. 2013

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“…On the other hand, one asks for very accurate measurements of aerosol loading and properties, which are very difficult to achieve in the vicinity of clouds (Koren et al, 2007(Koren et al, , 2008bCharlson et al, 2007;Wen et al, 2007). Even if assuming that one can measure correctly clouds and aerosol in a cloud field, the next challenge is due to the strong coupling of both to meteorology (environmental properties).…”

Section: Retrieval Artifacts and Meteorologymentioning

confidence: 99%

Aerosol-induced changes of convective cloud anvils produce strong climate warming

et al. 2010

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Abstract. The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. Small human-induced perturbations to cloud characteristics via aerosol pathways can create a change in the top-of-atmosphere radiative forcing of hundreds of Wm −2 . Here we focus on links between aerosol and deep convective clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting that the aerosol environment in each region is entirely different. The tops of these vertically developed clouds consisting of mostly ice can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing.We find that increased aerosol loading is associated with taller cloud towers and anvils. The taller clouds reach levels of enhanced wind speeds that act to spread and thin the anvil clouds, increasing areal coverage and decreasing cloud optical depth. The radiative effect of this transition is to create a positive radiative forcing (warming) at top-of-atmosphere.Furthermore we introduce the cloud optical depth (τ ), cloud height (Z) forcing space and show that underestimation of radiative forcing is likely to occur in cases of non homogenous clouds. Specifically, the mean radiative forcing of towers and anvils in the same scene can be several times greater than simply calculating the forcing from the mean cloud optical depth in the scene.Correspondence to: I. Koren (ilan.koren@weizmann.ac.il) Limitations of the method are discussed, alternative sources of aerosol loading are tested and meteorological variance is restricted, but the trend of taller clouds, increased and thinner anvils associated with increased aerosol loading remains robust through all the different tests and perturbations.

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“…Separating clouds and aerosols is inherently difficult because there exists no clearly defined separation between the two in any variable. This is an issue of measurement systems, but also an inherent physical continuum between aerosol particles, wet aerosol particles, activated cloud droplets and dissipated cloud fragments (Koren et al, 2007;Charlson et al, 2007). Remote sensing algorithms employ complicated schemes, using many variables (Ackerman et al, 1998;Frey et al, 2008), to make this separation as best they can, but no "cloud mask" is perfect.…”

Section: Introductionmentioning

confidence: 99%

Retrieving aerosol in a cloudy environment: aerosol product availability as a function of spatial resolution

et al. 2012

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Abstract. The challenge of using satellite observations to retrieve aerosol properties in a cloudy environment is to prevent contamination of the aerosol signal from clouds, while maintaining sufficient aerosol product yield to satisfy specific applications. We investigate aerosol retrieval availability at different instrument pixel resolutions using the standard MODIS aerosol cloud mask applied to MODIS data and supplemented with a new GOES-R cloud mask applied to GOES data for a domain covering North America and surrounding oceans. Aerosol product availability is not the same as the cloud free fraction and takes into account the techniques used in the MODIS algorithm to avoid clouds, reduce noise and maintain sufficient numbers of aerosol retrievals. The inherent spatial resolution of each instrument, 0.5 × 0.5 km for MODIS and 1 × 1 km for GOES, is systematically degraded to 1 × 1, 2 × 2, 1 × 4, 4 × 4 and 8 × 8 km resolutions and then analyzed as to how that degradation would affect the availability of an aerosol retrieval, assuming an aerosol product resolution at 8 × 8 km. The analysis is repeated, separately, for near-nadir pixels and those at larger view angles to investigate the effect of pixel growth at oblique angles on aerosol retrieval availability. The results show that as nominal pixel size increases, availability decreases until at 8 × 8 km 70 % to 85 % of the retrievals available at 0.5 km, nadir, have been lost. The effect at oblique angles is to further decrease availability over land but increase availability over ocean, because sun glint is found at near-nadir view angles. Finer resolution sensors (i.e., 1 × 1, 2 × 2 or even 1 × 4 km) will retrieve aerosols in partly cloudy scenes significantly more often than sensors with nadir views of 4 × 4 km or coarser. Large differences in the results of the two cloud masks designed for MODIS aerosol and GOES cloud products strongly reinforce that cloud masks must be developed with specific purposes in mind and that a generic cloud mask applied to an independent aerosol retrieval will likely fail.

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

Cited by 123 publications

References 46 publications

MODIS 3 km aerosol product: algorithm and global perspective

MODIS 3 km aerosol product: algorithm and global perspective

Aerosol-induced changes of convective cloud anvils produce strong climate warming

Retrieving aerosol in a cloudy environment: aerosol product availability as a function of spatial resolution

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