Estimate of satellite‐derived cloud optical thickness and effective radius errors and their effect on computed domain‐averaged irradiances

Kato, Seiji; Hinkelman, Laura M.; Cheng, Anning

doi:10.1029/2005jd006668

Cited by 52 publications

(70 citation statements)

References 35 publications

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“…These findings have not to be confused with results of others on the impact of cloud inhomogeneity and 3-D effects on effective radius retrievals, which are valid for effective radius values in the range of cloud particles (e.g. Marshak et al, 2006;Kato et al, 2006). Here the result is dominated by the pixels with drizzle sized particles and thus very large effective radii and the way the particular retrieval deals with these areas of very low optical thickness.…”

Section: Complex Case: Scattered Cumuluscontrasting

confidence: 44%

“…In this context the apparent differences to results of Marshak et al (2006) or Kato et al (2006) have to be mentioned once more. While these also evaluate the impact of 3-D effects and inhomogeneity on effective radius retrievals by means of LES cloud data and 3-D radiative transfer simulations, they investigate cloud particle sized effective radius variations and idealized, exemplary retrievals.…”

Section: Discussion and Outlookmentioning

confidence: 99%

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Testing remote sensing on artificial observations: impact of drizzle and 3-D cloud structure on effective radius retrievals

et al. 2010

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Abstract. Remote sensing of cloud effective particle size with passive sensors like the Moderate Resolution Imaging Spectroradiometer (MODIS) is an important tool for cloud microphysical studies. As a measure of the radiatively relevant droplet size, effective radius can be retrieved with different combinations of visible through shortwave and midwave infrared channels. In practice, retrieved effective radii from these combinations can be quite different. This difference is perhaps indicative of different penetration depths and path lengths for the spectral reflectances used. In addition, operational liquid water cloud retrievals are based on the assumption of a relatively narrow distribution of droplet sizes; the role of larger precipitation particles in these distributions is neglected. Therefore, possible explanations for the discrepancy in some MODIS spectral size retrievals could include 3-D radiative transport effects, including sub-pixel cloud inhomogeneity, and/or the impact of drizzle formation. For three cloud cases the possible factors of influence are isolated and investigated in detail by the use of simulated cloud scenes and synthetic satellite data: marine boundary layer cloud scenes from large eddy simulations (LES) with detailed microphysics are combined with Monte Carlo radiative transfer calculations that explicitly account for the detailed droplet size distributions as well as 3-D radiative transfer to simulate MODIS observations. The operational MODIS optical thickness and effective radius retrieval algorithm is applied to these and the results are compared to the given LES microphysics.We investigate two types of marine cloud situations each with and without drizzle from LES simulations: (1) a typical Correspondence to: T. Zinner (tobias.zinner@lmu.de) daytime stratocumulus deck at two times in the diurnal cycle and (2) one scene with scattered cumulus. Only small impact of drizzle formation on the retrieved domain average and on the differences between the three effective radius retrievals is noticed for both cloud scene types for different reasons. For our, presumably typical, overcast stratocumulus scenes with an optical thickness of 8 to 9 and rain rates at cloud bottom up to 0.05 mm/h clear drizzle impact on the retrievals can be excluded. The cumulus scene does not show much drizzle sensitivity either despite extended drizzle areas being directly visible from above (locally >1 mm/h), which is mainly due to technical characteristics of the standard retrieval approach. 3-D effects, on the other hand, produce large discrepancies between the 1.6 and 2.1 µm channel observations compared to 3.7 µm retrievals in the latter case. A general sensitivity of MODIS particle size data to drizzle formation is not corroborated by our case studies.

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Section: Complex Case: Scattered Cumuluscontrasting

confidence: 44%

Section: Discussion and Outlookmentioning

confidence: 99%

Testing remote sensing on artificial observations: impact of drizzle and 3-D cloud structure on effective radius retrievals

et al. 2010

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“…Figure 3 could arise for many reasons. In some cases of low LWP, the clouds are broken or scattered and R e is likely overestimated while τ c may be too small (Kato et al, 2006). It is also possible that the extinction from BB aerosols above the cloud could affect the retrieval of τ c and R e from satellite (Haywood et al, 2003;Wilcox et al, 2009) by reducing the reflectance at several wavelengths, especially for thin clouds.…”

Section: First Indirect Effectmentioning

confidence: 99%

Effect of biomass burning on marine stratocumulus clouds off the California coast

et al. 2009

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Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in June and July of 2006-2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses at 14:00 local time. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. Absorbing aerosols located above the marine boundary layer lead to an increase of the lower tropospheric stability and a reduction in the vertical entrainment of dry air from above, leading to increased cloud formation. The combined effect was an indirect radiative forcing of −7.5% ±1.7% (cooling effect) of the outgoing radiative flux at the top of the atmosphere on average, with a bias due to meteorology of +0.9%. FurtherCorrespondence to: J. Brioude (jerome.brioude@noaa.gov) away from the coast, the biomass burning aerosols, which were located within the boundary layer, reduced the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.3% ±0.3% (warming effect) with a bias of +0.5%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.

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“…The cloud albedo is not derived from a single view as computed in Kato et al (2006) at 1 km x 1 km but from every viewing angles. The multi-angular capabilities of POLDER allow then averaging of the different values using a directional weighting function.…”

Section: Description Of the Synthetic Generated Clouds And Radiative mentioning

confidence: 99%

“…Kato et al (2006) analyzed in addition the error on the cloud albedo, which is an important parameter for cloud radiative budget studies. At 1 km pixel size, they found significant errors ranging between -0.3% to 14% (-5% to 30%) from nadir (oblique view) depending on the cloud heterogeneity.…”

Section: Introductionmentioning

confidence: 99%

Cloud heterogeneity effects on cloud and aerosol above cloud properties retrieved from simulated total and polarized reflectances

Cornet¹,

C-Labonnote²,

Szczap³

et al. 2017

Preprint

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Abstract. Simulations of total and polarized cloud reflectance angular signatures such as the ones measured by the multiangular and polarized radiometer POLDER3/PARASOL are used to evaluate cloud heterogeneity effects on cloud parameter retrievals. Effects on optical thickness, cloud albedo, effective radius and variance of the cloud droplet size distribution and aerosol above cloud optical thickness are analyzed. Three different clouds having the same mean optical thicknesses were 15 generated: the first one with a flat top, the second one with a bumpy top and the last one with a fractional cloud cover. At small scale (50 m), for oblique solar incidence, the illumination effects lead to higher total but also polarized reflectances.The polarized reflectances even reach values that cannot be predicted by the 1D homogeneous cloud assumption. At the POLDER scale (7 km x 7 km), the angular signature is modified by a combination of the plane-parallel bias and the shadowing and illumination effects. In order to quantify effects of cloud heterogeneity on operational products, we ran the 20 POLDER operational algorithms on the simulated reflectances to retrieve the cloud optical thickness and albedo. Results show that the cloud optical thickness is greatly affected: biases can reach up to -70%, -50% or +40% for backward, nadir and forward viewing directions respectively. Concerning the cloud albedo, the errors are smaller, between -4.7% for solar incidence angle of 20° and up to about 8% for solar incidence angle of 60°. We also tested the heterogeneity effects on new algorithms that allow retrieving cloud droplet size distribution and cloud top pressures and also aerosol above clouds. 25Contrarily to the bi-spectral method, the retrieved cloud droplet size parameters are not significantly affected by the cloud heterogeneity, which proves to be a great advantage of using polarized measurements. However the cloud top pressure obtained from molecular scattering in the forward direction can be biased up to 120 hPa (around 1 km). Concerning the aerosol optical thickness (AOT) above cloud, the results are different depending on the available angular information. Above the fractional cloud, when only side scattering angles are available, the AOT can be underestimated because of the plane-30 parallel bias. For solar zenith angle of 60°, on contrary, it is overestimated because the polarized reflectances are increased in forward directions.Atmos. Meas. Tech. Discuss., https://doi

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Estimate of satellite‐derived cloud optical thickness and effective radius errors and their effect on computed domain‐averaged irradiances

Cited by 52 publications

References 35 publications

Testing remote sensing on artificial observations: impact of drizzle and 3-D cloud structure on effective radius retrievals

Testing remote sensing on artificial observations: impact of drizzle and 3-D cloud structure on effective radius retrievals

Effect of biomass burning on marine stratocumulus clouds off the California coast

Cloud heterogeneity effects on cloud and aerosol above cloud properties retrieved from simulated total and polarized reflectances

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