Combined observational and modeling based study of the aerosol indirect effect

Abstract. The indirect effect of aerosols via liquid clouds is investigated by comparing aerosol and cloud characteristics from the Global Climate Model CAM-Oslo to those observed by the MODIS instrument onboard the TERRA and AQUA satellites (http://modis.gsfc.nasa.gov). The comparison is carried out for 15 selected regions ranging from remote and clean to densely populated and polluted. For each region, the regression coefficient and correlation coefficient for the following parameters are calculated: Aerosol Optical Depth vs. Liquid Cloud Optical Thickness, Aerosol Optical Depth vs. Liquid Cloud Droplet Effective Radius and Aerosol Optical Depth vs. Cloud Liquid Water Path. Modeled and observed correlation coefficients and regression coefficients are then compared for a 3-year period starting in January 2001. Additionally, global maps for a number of aerosol and cloud parameters crucial for the understanding of the aerosol indirect effect are compared for the same period of time. Significant differences are found between MODIS and CAM-Oslo both in the regional and global comparison. However, both the model and the observations show a positive correlation between Aerosol Optical Depth and Cloud Optical Depth in practically all regions and for all seasons, in agreement with the current understanding of aerosol-cloud interactions. The correlation between Aerosol Optical Depth and Liquid Cloud Droplet Effective Radius is variable both in the model and the observations. However, the model reports the expected negative correlation more often than the MODIS data. Aerosol Optical Depth is overall positively correlated to Cloud Liquid Water Path both in the model and the observations, with a few regional exceptions.

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Combined observational and modeling based study of the aerosol indirect effect

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-3583-2006 ◽

2006 ◽

Vol 6 (11) ◽

pp. 3583-3601 ◽

Cited By ~ 28

Author(s):

T. Storelvmo ◽

J. E. Kristjánsson ◽

G. Myhre ◽

M. Johnsrud ◽

F. Stordal

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Liquid Water ◽

Indirect Effect ◽

Cloud Droplet ◽

Effective Radius ◽

Liquid Water Path ◽

Cloud Liquid Water ◽

Aerosol Indirect Effect ◽

Cloud Liquid Water Path

Abstract. The indirect effect of aerosols via liquid clouds is investigated by comparing aerosol and cloud characteristics from the Global Climate Model CAM-Oslo to those observed by the MODIS instrument onboard the TERRA and AQUA satellites http://modis.gsfc.nasa.gov). The comparison is carried out for 15 selected regions ranging from remote and clean to densely populated and polluted. For each region, the regression coefficient and correlation coefficient for the following parameters are calculated: Aerosol Optical Depth vs. Liquid Cloud Optical Thickness, Aerosol Optical Depth vs. Liquid Cloud Droplet Effective Radius and Aerosol Optical Depth vs. Cloud Liquid Water Path. Modeled and observed correlation coefficients and regression coefficients are then compared for a 3-year period starting in January 2001. Additionally, global maps for a number of aerosol and cloud parameters crucial for the understanding of the aerosol indirect effect are compared for the same period of time. Significant differences are found between MODIS and CAM-Oslo both in the regional and global comparison. However, both the model and the observations show a positive correlation between Aerosol Optical Depth and Cloud Optical Depth in practically all regions and for all seasons, in agreement with the current understanding of aerosol-cloud interactions. The correlation between Aerosol Optical Depth and Liquid Cloud Droplet Effective Radius is variable both in the model and the observations. However, the model reports the expected negative correlation more often than the MODIS data. Aerosol Optical Depth is overall positively correlated to Cloud Liquid Water Path both in the model and the observations, with a few regional exceptions.

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Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-9851-2010 ◽

2010 ◽

Vol 10 (20) ◽

pp. 9851-9861 ◽

Cited By ~ 12

Author(s):

X. Ma ◽

K. von Salzen ◽

J. Cole

Keyword(s):

Liquid Water ◽

Negative Relationship ◽

Cloud Droplet ◽

Global Scale ◽

Effective Radius ◽

Liquid Water Path ◽

Cloud Droplets ◽

Cloud Liquid Water ◽

Albedo Effect ◽

Cloud Liquid Water Path

Abstract. Satellite-based cloud top effective radius retrieved by the CERES Science Team were combined with simulated aerosol concentrations from CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS Science Team.

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Constraints on first aerosol indirect effect from a combination of MODIS-CERES satellite data and global climate simulations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-13945-2010 ◽

2010 ◽

Vol 10 (6) ◽

pp. 13945-13968

Author(s):

X. Ma ◽

K. von Salzen ◽

J. Cole

Keyword(s):

Liquid Water ◽

Indirect Effect ◽

Global Climate ◽

Negative Relationship ◽

Cloud Droplet ◽

Global Scale ◽

Effective Radius ◽

Liquid Water Path ◽

Cloud Droplets ◽

Cloud Liquid Water

Abstract. Retrievals of cloud top effective radius from MODIS (as derived by CERES) were combined with aerosol concentrations from the CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS science team.

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Is positive correlation between cloud droplet effective radius and aerosol optical depth over land due to retrieval artifacts or real physical processes?

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-8879-2019 ◽

2019 ◽

Vol 19 (13) ◽

pp. 8879-8896 ◽

Cited By ~ 4

Author(s):

Hailing Jia ◽

Xiaoyan Ma ◽

Johannes Quaas ◽

Yan Yin ◽

Tom Qiu

Keyword(s):

Aerosol Optical Depth ◽

Optical Depth ◽

Radiant Energy ◽

Single Layer ◽

Cloud Droplet ◽

Energy System ◽

Effective Radius ◽

Liquid Water Path ◽

Anthropogenic Aerosol ◽

Aerosol Cloud

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.

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MBL drizzle properties and their impact on cloud property retrievals

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-4307-2015 ◽

2015 ◽

Vol 8 (4) ◽

pp. 4307-4323

Author(s):

P. Wu ◽

X. Dong ◽

B. Xi

Keyword(s):

Liquid Water ◽

Cloud Droplet ◽

Number Concentration ◽

Effective Radius ◽

Liquid Water Path ◽

Water Path ◽

Cloud Property ◽

Annual Means ◽

Mean Differences ◽

The Impact

Abstract. In this study, we retrieve and document drizzle properties, and investigate the impact of drizzle on cloud property retrievals from ground-based measurements at the ARM Azores site from June 2009 to December 2010. For the selected cloud and drizzle samples, the drizzle occurrence is 42.6% with a maximum of 55.8% in winter and a minimum of 35.6% in summer. The annual means of drizzle liquid water path LWPd, effective radius rd, and number concentration Nd for the rain (virga) samples are 5.48 (1.29) g m−2, 68.7 (39.5) μm, and 0.14 (0.38) cm−3. The seasonal mean LWPd values are less than 4% of the MWR-retrieved LWP values. The annual mean differences in cloud-droplet effective radius with and without drizzle are 0.12 and 0.38 μm, respectively, for the virga and rain samples. Therefore, we conclude that the impact of drizzle on cloud property retrievals is insignificant at the ARM Azores site.

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An intercomparison of radar-based liquid cloud microphysics retrievals and implication for model evaluation studies

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-4-7109-2011 ◽

2011 ◽

Vol 4 (6) ◽

pp. 7109-7158 ◽

Cited By ~ 1

Author(s):

D. Huang ◽

C. Zhao ◽

M. Dunn ◽

X. Dong ◽

G. G. Mace ◽

...

Keyword(s):

Great Plains ◽

Liquid Water ◽

Model Evaluation ◽

Evaluation Studies ◽

Cloud Droplet ◽

Liquid Water Content ◽

Cloud Microphysics ◽

Effective Radius ◽

High Altitudes ◽

Liquid Water Path

Abstract. To assess if current radar-based liquid cloud microphysical retrievals of the Atmospheric Radiation Measurement (ARM) program can provide useful constraints for modeling studies, this paper presents intercomparison results of three cloud products at the Southern Great Plains (SGP) site: the ARM MICROBASE, University of Utah (UU), and University of North Dakota (UND) products over the nine-year period from 1998 to 2006. The probability density and spatial autocorrelation functions of the three cloud Liquid Water Content (LWC) retrievals appear to be consistent with each other, while large differences are found in the droplet effective radius retrievals. The differences in the vertical distribution of both cloud LWC and droplet effective radius retrievals are found to be alarmingly large, with the relative difference between nine-year mean cloud LWC retrievals ranging from 20% at low altitudes to 100% at high altitudes. Nevertheless, the spread in LWC retrievals is much smaller than that in cloud simulations by climate and cloud resolving models. The MICROBASE effective radius ranges from 2.0 at high altitudes to 6.0 μm at low altitudes and the UU and UND droplet effective radius is 6 μm larger. Further analysis through a suite of retrieval experiments shows that the difference between MICROBASE and UU LWC retrievals stems primarily from the partition total Liquid Water path (LWP) into supercooled and warm liquid, and from the input cloud boundaries and LWP. The large differences between MICROBASE and UU droplet effective radius retrievals are mainly due to rain/drizzle contamination and the assumptions of cloud droplet concentration used in the retrieval algorithms. The large discrepancy between different products suggests caution in model evaluation with these observational products, and calls for improved retrievals in general.

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Statistical characteristics of cloud variability. Part 1: Retrieved cloud liquid water path at three ARM sites

Journal of Geophysical Research Atmospheres ◽

10.1002/2014jd022001 ◽

2014 ◽

Vol 119 (18) ◽

pp. 10,813-10,828 ◽

Cited By ~ 5

Author(s):

Dong Huang ◽

Edwin Campos ◽

Yangang Liu

Keyword(s):

Liquid Water ◽

Statistical Characteristics ◽

Liquid Water Path ◽

Cloud Liquid Water ◽

Water Path ◽

Cloud Liquid Water Path

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Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part I: Calculation of SW Flux from Observed Cloud Properties*

Journal of Climate ◽

10.1175/jcli-d-14-00287.1 ◽

2014 ◽

Vol 27 (23) ◽

pp. 8836-8857 ◽

Cited By ~ 28

Author(s):

Daniel T. McCoy ◽

Dennis L. Hartmann ◽

Daniel P. Grosvenor

Keyword(s):

Seasonal Variation ◽

Solar Radiation ◽

Southern Ocean ◽

Water Content ◽

Liquid Water ◽

Effective Radius ◽

Shortwave Radiation ◽

Liquid Water Path ◽

Cloud Liquid Water ◽

Cloud Properties

Abstract The sensitivity of the reflection of shortwave radiation over the Southern Ocean to the cloud properties there is estimated using observations from a suite of passive and active satellite instruments in combination with radiative transfer modeling. A composite cloud property observational data description is constructed that consistently incorporates mean cloud liquid water content, ice water content, liquid and ice particle radius information, vertical structure, vertical overlap, and spatial aggregation of cloud water as measured by optical depth versus cloud-top pressure histograms. The observational datasets used are Moderate Resolution Imaging Spectroradiometer (MODIS) effective radius filtered to mitigate solar zenith angle bias, the Multiangle Imaging Spectroradiometer (MISR) cloud-top height–optical depth (CTH–OD) histogram, the liquid water path from the University of Wisconsin dataset, and ice cloud properties from CloudSat. This cloud database is used to compute reflected shortwave radiation as a function of month and location over the ocean from 40° to 60°S, which compares well with observations of reflected shortwave radiation. This calculation is then used to test the sensitivity of the seasonal variation of shortwave reflection to the observed seasonal variation of cloud properties. Effective radius decreases during the summer season, which results in an increase in reflected solar radiation of 4–8 W m−2 during summer compared to what would be reflected if the effective radius remained constant at its annual-mean value. Summertime increases in low cloud fraction similarly increase the summertime reflection of solar radiation by 9–11 W m−2. In-cloud liquid water path is less in summertime, causing the reflected solar radiation to be 1–4 W m−2 less.

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