scholarly journals Effects of Surface Albedo on Cloud and Radiation Processes in Cloud-Resolving Model Simulations

2010 ◽  
Vol 67 (5) ◽  
pp. 1474-1491 ◽  
Author(s):  
Sunwook Park ◽  
Xiaoqing Wu
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Critical Value ◽  
Cloud Base ◽  
Radiative Fluxes ◽  
Cloud Properties ◽  
Cloud Resolving Model ◽  
Albedo Effect ◽  
Evolving Surface ◽  
Radiation Processes

Abstract The relationship among the surface albedo, cloud properties, and radiative fluxes is investigated for the first time using a year-long cloud-resolving model (CRM) simulation with the prescribed evolving surface albedo. In comparison with the run using a fixed surface albedo, the CRM with the observed surface albedo represents the shortwave radiative budget closer to the observations in the winter. The greater surface albedo induces weaker instability in the low troposphere so that the amount of low clouds decreases during the winter. This reduces the shortwave and longwave cloud radiative forcing at the surface. The analysis of the CRM simulations with the evolving surface albedo reveals that there is a critical value (0.35) of the surface albedo. For albedos greater than the critical value, the upward shortwave flux at the top of the atmosphere (TOA) is positively proportional to the surface albedos when optically thin clouds exist, and is not much affected by reflection on the cloud top. If optically thick clouds occur and the surface albedo is greater than the critical value, the upward shortwave flux at the TOA is significantly influenced by the reflection of cloud top, but not much affected by the surface albedo. In addition, for albedos larger than the critical value, the downward shortwave flux at the surface is primarily influenced by the surface albedo and the reflection from the cloud base if optically thick clouds occur. However, the downward shortwave flux at the surface is not significantly affected by the surface albedo when optically thin clouds exist because the reflection on the cloud base is weak. When surface albedos are less than the critical value, those relationships among surface albedo, shortwave flux, and cloud properties are not obvious. The surface albedo effect on shortwave flux increases as solar zenith angle (SZA) decreases, but its dependence on the SZA is negligible when optically thick clouds exist.

scholarly journals Surface and top-of-atmosphere radiative feedback kernels for CESM-CAM5

2018 ◽  
Vol 10 (1) ◽  
pp. 317-324 ◽  
Author(s):  
Angeline G. Pendergrass ◽  
Andrew Conley ◽  
Francis M. Vitt
Keyword(s):  
Water Vapor ◽  
Greenhouse Gases ◽  
Surface Temperature ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Large Ensemble ◽  
Radiative Fluxes ◽  
Radiative Feedback ◽  
Ensemble Simulations ◽  
Temperature Water

Abstract. Radiative kernels at the top of the atmosphere are useful for decomposing changes in atmospheric radiative fluxes due to feedbacks from atmosphere and surface temperature, water vapor, and surface albedo. Here we describe and validate radiative kernels calculated with the large-ensemble version of CAM5, CESM1.1.2, at the top of the atmosphere and the surface. Estimates of the radiative forcing from greenhouse gases and aerosols in RCP8.5 in the CESM large-ensemble simulations are also diagnosed. As an application, feedbacks are calculated for the CESM large ensemble. The kernels are freely available at https://doi.org/10.5065/D6F47MT6, and accompanying software can be downloaded from https://github.com/apendergrass/cam5-kernels.

scholarly journals A critical look at spatial scale choices in satellite-based aerosol indirect effect studies

2010 ◽  
Vol 10 (23) ◽  
pp. 11459-11470 ◽  
Author(s):  
B. S. Grandey ◽  
P. Stier
Keyword(s):  
Radiative Forcing ◽  
Spatial Scales ◽  
Cloud Droplet ◽  
Spatial Variations ◽  
Opposite Pattern ◽  
Cloud Properties ◽  
Methodological Errors ◽  
Albedo Effect ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. Analysing satellite datasets over large regions may introduce spurious relationships between aerosol and cloud properties due to spatial variations in aerosol type, cloud regime and synoptic regime climatologies. Using MODerate resolution Imaging Spectroradiometer data, we calculate relationships between aerosol optical depth τa derived liquid cloud droplet effective number concentration Ne and liquid cloud droplet effective radius re at different spatial scales. Generally, positive values of dlnNedlnτa are found for ocean regions, whilst negative values occur for many land regions. The spatial distribution of dlnredlnτa shows approximately the opposite pattern, with generally postive values for land regions and negative values for ocean regions. We find that for region sizes larger than 4° × 4°, spurious spatial variations in retrieved cloud and aerosol properties can introduce widespread significant errors to calculations of dlnNedlnτa and dlnredlnτa. For regions on the scale of 60° × 60°, these methodological errors may lead to an overestimate in global cloud albedo effect radiative forcing of order 80% relative to that calculated for regions on the scale of 1° × 1°.

Estimating Cloud Optical Depth from Surface Radiometric Observations: Sensitivity to Instrument Noise and Aerosol Contamination

2005 ◽  
Vol 62 (11) ◽  
pp. 4095-4104 ◽  
Author(s):  
Alain Beaulne ◽  
Howard W. Barker ◽  
Jean-Pierre Blanchet
Keyword(s):  
Optical Depth ◽  
Surface Albedo ◽  
Transport Model ◽  
Cloud Base ◽  
Spectral Difference ◽  
Cloud Optical Depth ◽  
Sensitivity Tests ◽  
Cloud Resolving Model ◽  
Model Cloud ◽  
Instrument Noise

Abstract The spectral-difference algorithm of Barker and Marshak for inferring optical depth τ of broken clouds has been shown numerically to be potentially useful. Their method estimates cloud-base reflectance and τ using spectral radiometric measurements made at the surface at two judiciously chosen wavelengths. Here it is subject to sensitivity tests that address the impacts of two ubiquitous sources of potential error: instrument noise and presence of aerosol. Experiments are conducted using a Monte Carlo photon transport model, cloud-resolving model data, and surface albedo data from satellite observations. The objective is to analyze the consistency between inherent and retrieved values of τ. Increasing instrument noise, especially if uncorrelated at both wavelengths, decreases retrieved cloud fraction and increases retrieved mean τ. As with all methods that seek to infer τ using passive radiometry, the presence of aerosol requires that threshold values be set in order to discriminate between cloudy and cloud-free columns. A technique for estimating thresholds for cloudy columns is discussed and demonstrated. Finally, it was found that surface type and mean inherent τ play major roles in defining retrieval accuracy.

scholarly journals Observed correlations between aerosol and cloud properties in an Indian Ocean trade cumulus regime

2015 ◽  
Vol 15 (20) ◽  
pp. 29347-29402 ◽  
Author(s):  
K. Pistone ◽  
P. S. Praveen ◽  
R. M. Thomas ◽  
V. Ramanathan ◽  
E. Wilcox ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Indian Ocean ◽  
Liquid Water ◽  
Radiative Forcing ◽  
Cloud Base ◽  
Future Research ◽  
Air Mass ◽  
Vapor Flux ◽  
Cloud Properties

Abstract. There are many contributing factors which determine the micro- and macrophysical properties of clouds, including atmospheric structure, dominant meteorological conditions, and aerosol concentration, all of which may be coupled to one another. In the quest to determine aerosol effects on clouds, these potential relationships must be understood, as changes in atmospheric conditions due to aerosol may change the expected magnitude of indirect effects by altering cloud properties in unexpected ways. Here we describe several observed correlations between aerosol conditions and cloud and atmospheric properties in the Indian Ocean winter monsoon season. In the CARDEX (Cloud, Aerosol, Radiative forcing, Dynamics EXperiment) field campaign conducted in February and March 2012 in the northern Indian Ocean, continuous measurements of atmospheric precipitable water vapor and the liquid water path (LWP) of trade cumulus clouds were made, concurrent with measurements of water vapor flux, cloud and aerosol vertical profiles, meteorological data, and surface and total-column aerosol. Here we present evidence of a positive correlation between aerosol and cloud LWP which becomes clear after the data are filtered to control for the natural meteorological variability in the region. We then use the aircraft and ground observatory measurements to explore the mechanisms behind the observed aerosol–LWP correlation. We determine that increased boundary-layer humidity lowering the cloud base is responsible for the observed increase in cloud liquid water. Large-scale analysis indicates that high pollution cases originate with a highly-polluted boundary layer air mass approaching the observatory from a northwesterly direction. This polluted mass exhibits higher temperatures and humidity than the clean case, the former of which may be attributable to heating due to aerosol absorption of solar radiation over the subcontinent. While high temperature conditions dispersed along with the high-aerosol anomaly, the high humidity condition was observed to instead develop along with the polluted air mass. We then explore potential causal mechanisms of the observed correlations, though future research will be needed to more fully describe the aerosol–humidity relationship.

scholarly journals The scale problem in quantifying aerosol indirect effects

2011 ◽  
Vol 11 (9) ◽  
pp. 26741-26789 ◽  
Author(s):  
A. McComiskey ◽  
G. Feingold
Keyword(s):  
Indirect Effects ◽  
Radiative Forcing ◽  
Liquid Water Path ◽  
Aerosol Indirect Effects ◽  
Remote Sensors ◽  
Cloud Properties ◽  
Wide Range ◽  
Albedo Effect ◽  
Cloud Liquid Water Path ◽  
The Impact

Abstract. A wide range of estimates exists for the radiative forcing of the aerosol effect on cloud albedo. We argue that a component of this uncertainty derives from the use of a wide range of observational scales and platforms. Aerosol affects cloud properties at the microphysical scale, or the "process scale" but observations are most often made of bulk properties over a wide range of resolutions, or "analysis scales". We show that differences between process and analysis scales incur biases in quantification of the albedo effect through the impact that data aggregation has on statistical properties of the aerosol or cloud variable, and their covariance. Measures made within this range of scales are erroneously treated as equivalent, leading to a large uncertainty in associated radiative forcing estimates. Issues associated with the coarsening of observational resolution particular to quantifying the albedo effect are discussed. Specifically, the omission of the constraint on cloud liquid water path and the separation in space of cloud and aerosol properties from passive, space-based remote sensors dampen the measured strength of the albedo effect. Based on our understanding of these biases we propose a new approach for an observationally-based, robust method for estimating aerosol indirect effects that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.

scholarly journals The scale problem in quantifying aerosol indirect effects

2012 ◽  
Vol 12 (2) ◽  
pp. 1031-1049 ◽  
Author(s):  
A. McComiskey ◽  
G. Feingold
Keyword(s):  
Radiative Forcing ◽  
Process Model ◽  
Full Range ◽  
Liquid Water Path ◽  
Aerosol Cloud ◽  
Cloud Properties ◽  
Wide Range ◽  
Albedo Effect ◽  
Aerosol Cloud Interactions ◽  
The Impact

Abstract. A wide range of estimates exists for the radiative forcing of the aerosol effect on cloud albedo. We argue that a component of this uncertainty derives from the use of a wide range of observational scales and platforms. Aerosol influences cloud properties at the microphysical scale, or the "process scale", but observations are most often made of bulk properties over a wide range of resolutions, or "analysis scales". We show that differences between process and analysis scales incur biases in quantification of the albedo effect through the impact that data aggregation and computational approach have on statistical properties of the aerosol or cloud variable, and their covariance. Measures made within this range of scales are erroneously treated as equivalent, leading to a large uncertainty in associated radiative forcing estimates. Issues associated with the coarsening of observational resolution particular to quantifying the albedo effect are discussed. Specifically, the omission of the constraint on cloud liquid water path and the separation in space of cloud and aerosol properties from passive, space-based remote sensors dampen the measured strength of the albedo effect. We argue that, because of this lack of constraints, many of these values are in fact more representative of the full range of aerosol-cloud interactions and their associated feedbacks. Based on our understanding of these biases we propose a new observationally-based and process-model-constrained, method for estimating aerosol-cloud interactions that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.

scholarly journals A critical look at spatial scale choices in satellite-based aerosol indirect effect studies

2010 ◽  
Vol 10 (6) ◽  
pp. 15417-15440 ◽  
Author(s):  
B. S. Grandey ◽  
P. Stier
Keyword(s):  
Radiative Forcing ◽  
Spatial Scales ◽  
Cloud Droplet ◽  
Spatial Variations ◽  
Opposite Pattern ◽  
Cloud Properties ◽  
Methodological Errors ◽  
Albedo Effect ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. Analysing satellite datasets over large regions may introduce spurious relationships between aerosol and cloud properties due to spatial variations in aerosol type, cloud regime and synoptic regime climatologies. Using MODerate resolution Imaging Spectroradiometer data, we calculate relationships between aerosol optical depth τa, derived liquid cloud droplet effective number concentration Ne and liquid cloud droplet effective radius re at different spatial scales. Generally, positive values of dlnNe dlnτa are found for ocean regions, whilst negative values occur for many land regions. The spatial distribution of dlnre dlnτa shows approximately the opposite pattern, with generally postive values for land regions and negative values for ocean regions. We find that for region sizes larger than 4°×4°, spurious spatial variations in retrieved cloud and aerosol properties can introduce widespread significant errors to calculations of dlnNe dlnτa and dlnre dlnτa . For regions on the scale of 60°×60°, these methodological errors may lead to an overestimate in global cloud albedo effect radiative forcing of order 80%.

scholarly journals Climatic Impact of Global-Scale Deforestation: Radiative versus Nonradiative Processes

2010 ◽  
Vol 23 (1) ◽  
pp. 97-112 ◽  
Author(s):  
Edouard L. Davin ◽  
Nathalie de Noblet-Ducoudré
Keyword(s):  
Surface Roughness ◽  
Land Cover ◽  
Land Cover Change ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Global Scale ◽  
Ocean Coupling ◽  
Albedo Effect ◽  
Change Impact ◽  
Nonradiative Processes

Abstract A fully coupled land–ocean–atmosphere GCM is used to explore the biogeophysical impact of large-scale deforestation on surface climate. By analyzing the model sensitivity to global-scale replacement of forests by grassland, it is shown that the surface albedo increase owing to deforestation has a cooling effect of −1.36 K globally. On the other hand, forest removal decreases evapotranspiration efficiency and decreases surface roughness, both leading to a global surface warming of 0.24 and 0.29 K, respectively. The net biogeophysical impact of deforestation results from the competition between these effects. Globally, the albedo effect is dominant because of its wider-scale impact, and the net biogeophysical impact of deforestation is thus a cooling of −1 K. Over land, the balance between the different processes varies with latitude. In temperate and boreal zones of the Northern Hemisphere the albedo effect is stronger and deforestation thus induces a cooling. Conversely, in the tropics the net impact of deforestation is a warming, because evapotranspiration efficiency and surface roughness provide the dominant influence. The authors also explore the importance of the ocean coupling in shaping the climate response to deforestation. First, the temperature over ocean responds to the land cover perturbation. Second, even the temperature change over land is greatly affected by the ocean coupling. By assuming fixed oceanic conditions, the net effect of deforestation, averaged over all land areas, is a warming, whereas taking into account the coupling with the ocean leads, on the contrary, to a net land cooling. Furthermore, it is shown that the main parameter involved in the coupling with the ocean is surface albedo. Indeed, a change in albedo modifies temperature and humidity in the whole troposphere, thus enabling the initially land-confined perturbation to be transferred to the ocean. Finally, the radiative forcing framework is discussed in the context of land cover change impact on climate. The experiments herein illustrate that deforestation triggers two opposite types of forcing mechanisms—radiative forcing (owing to surface albedo change) and nonradiative forcing (owing to change in evapotranspiration efficiency and surface roughness)—that exhibit a similar magnitude globally. However, when applying the radiative forcing concept, nonradiative processes are ignored, which may lead to a misrepresentation of land cover change impact on climate.

scholarly journals Surface and top-of-atmosphere radiative feedback kernels for CESM-CAM5

2017 ◽  
Author(s):  
Angeline G. Pendergrass ◽  
Andrew Conley ◽  
Francis Vitt
Keyword(s):  
Water Vapor ◽  
Greenhouse Gases ◽  
Surface Temperature ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Large Ensemble ◽  
Radiative Fluxes ◽  
Radiative Feedback ◽  
Ensemble Simulations ◽  
Temperature Water

Abstract. Radiative kernels at the top of atmosphere are useful for decomposing changes in atmospheric radiative fluxes due to feedbacks from atmosphere and surface temperature, water vapor, and surface albedo. Here we describe and validate radiative kernels calculated with the large-ensemble version of CAM5, CESM 1.1.2, at the top-of-atmosphere and the surface. Estimates of the radiative forcing from greenhouse gases and aerosols in RCP8.5 in the CESM large ensemble simulations are also included. As an application, feedbacks are calculated for the CESM large ensemble. The kernels are freely available at https://zenodo.org/record/997902, and accompanying software can be downloaded from https://github.com/apendergrass/cam5-kernels.

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