scholarly journals Quantifying the Dependence of Satellite Cloud Retrievals on Instrument Uncertainty

2017 ◽  
Vol 30 (17) ◽  
pp. 6959-6976 ◽  
Author(s):  
Yolanda L. Shea ◽  
Bruce A. Wielicki ◽  
Sunny Sun-Mack ◽  
Patrick Minnis
Keyword(s):  
Climate Change ◽  
Optical Thickness ◽  
Indirect Effect ◽  
Effective Temperature ◽  
Radiative Forcing ◽  
Cloud Fraction ◽  
Effective Radius ◽  
Aerosol Indirect Effect ◽  
Sources Of Uncertainty ◽  
Water Cloud

Cloud response to Earth’s changing climate is one of the largest sources of uncertainty among global climate model (GCM) projections. Two of the largest sources of uncertainty are the spread in equilibrium climate sensitivity (ECS) and uncertainty in radiative forcing due to uncertainty in the aerosol indirect effect. Satellite instruments with sufficient accuracy and on-orbit stability to detect climate change–scale trends in cloud properties will improve confidence in the understanding of the relationship between observed climate change and cloud property trends, thus providing information to better constrain ECS and radiative forcing. This study applies a climate change uncertainty framework to quantify the impact of measurement uncertainty on trend detection times for cloud fraction, effective temperature, optical thickness, and water cloud effective radius. Although GCMs generally agree that the total cloud feedback is positive, disagreement remains on its magnitude. With the climate uncertainty framework, it is demonstrated how stringent measurement uncertainty requirements for reflected solar and infrared satellite measurements enable improved constraint of SW and LW cloud feedbacks and the ECS by significantly reducing trend uncertainties for cloud fraction, optical thickness, and effective temperature. The authors also demonstrate improved constraint on uncertainty in the aerosol indirect effect by reducing water cloud effective radius trend uncertainty.

scholarly journals Model intercomparison of indirect aerosol effects

2006 ◽  
Vol 6 (1) ◽  
pp. 1579-1617 ◽  
Author(s):  
J. E. Penner ◽  
J. Quaas ◽  
T. Storelvmo ◽  
T. Takemura ◽  
O. Boucher ◽  
...  
Keyword(s):  
Liquid Water ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
Cloud Fraction ◽  
Liquid Water Path ◽  
Aerosol Indirect Effect ◽  
Water Path ◽  
Series Of Experiments ◽  
Aerosol Effects ◽  
Indirect Forcing

Abstract. Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol indirect effect for the first experiment is rather similar. Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Nevertheless, these changes do not necessarily lead to large changes in the radiative forcing. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model ''noise''. The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models. Thus, this aspect of modeling requires significant improvement in order to improve the prediction of aerosol indirect effects.

scholarly journals Exploring the First Aerosol Indirect Effect over the Maritime Continent Using a Ten-Year Collocated MODIS, CALIOP, and Model Dataset

2018 ◽  
Author(s):  
Alexa D. Ross ◽  
Robert E. Holz ◽  
Gregory Quinn ◽  
Jeffrey S. Reid ◽  
Peng Xian ◽  
...  
Keyword(s):  
Indirect Effect ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Effective Radius ◽  
Satellite Observations ◽  
Orthogonal Polarization ◽  
High Background ◽  
Aerosol Indirect Effect ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Complex Relationships

Abstract. Satellite observations and model simulations cannot, by themselves, give full insight into the complex relationships between aerosols and clouds. This is especially the case over the greater Southeast Asia, an area that is particularly sensitive to changes in precipitation yet possesses some of the world’s largest observability and predictability challenges. We present a new collocated dataset that combines satellite observations from Aqua's Moderate-resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) with the Navy Aerosol Analysis and Prediction System (NAAPS). The dataset is designed with the capability to investigate aerosol-cloud relationships and provides coincident and vertically resolved cloud and aerosol observations for a ten-year period. Using model reanalysis aerosol fields from the NAAPS and coincident cloud liquid effective radius retrievals from MODIS (removing cirrus contamination using CALIOP), we investigate the first aerosol indirect effect. We find overall that as expected, aerosol loading anti-correlates with cloud effective radius, with maximum sensitivity in cumulous mediocris clouds with heights in the 3–4.5 km level. The highest susceptibility in droplet effective radius to modeled perturbations in particle concentrations were found in the more remote regions of the western Pacific Ocean and Indian Ocean. Conversely, there was much less variability in cloud droplet size near emission sources over both land and water. We hypothesize this is suggestive of a high background aerosol population already saturating the cloud condensation nuclei budget.

scholarly journals A spectral method for discriminating thermodynamic phase and retrieving cloud optical thickness and effective radius using transmitted solar radiance spectra

2015 ◽  
Vol 8 (3) ◽  
pp. 1361-1383 ◽  
Author(s):  
S. E. LeBlanc ◽  
P. Pilewskie ◽  
K. S. Schmidt ◽  
O. Coddington
Keyword(s):  
Root Mean Square ◽  
Optical Thickness ◽  
Liquid Water ◽  
Effective Radius ◽  
Least Square ◽  
Mean Square ◽  
Ice Cloud ◽  
Cloud Optical Thickness ◽  
Water Cloud ◽  
Thermodynamic Phase

Abstract. A new retrieval scheme for cloud optical thickness, effective radius, and thermodynamic phase was developed for ground-based measurements of cloud shortwave solar spectral transmittance. Fifteen parameters were derived to quantify spectral variations in shortwave transmittance due to absorption and scattering of liquid water and ice clouds, manifested by shifts in spectral slopes, curvatures, maxima, and minima. To retrieve cloud optical thickness and effective particle radius, a weighted least square fit that matched the modeled parameters was applied. The measurements for this analysis were made with the ground-based Solar Spectral Flux Radiometer in Boulder, Colorado, between May 2012 and January 2013. We compared the cloud optical thickness and effective radius from the new retrieval to two other retrieval methods. By using multiple spectral features, we find a closer fit (with a root mean square difference over the entire spectra of 3.1% for a liquid water cloud and 5.9% for an ice cloud) between measured and modeled spectra compared to two other retrieval methods which diverge by a root mean square of up to 6.4% for a liquid water cloud and 22.5% for an ice cloud. The new retrieval introduced here has an average uncertainty in effective radius (± 1.2 μm) smaller by factor of at least 2.5 than two other methods when applied to an ice cloud.

scholarly journals The Plane-Parallel Albedo Bias of Liquid Clouds from MODIS Observations

2007 ◽  
Vol 20 (20) ◽  
pp. 5114-5125 ◽  
Author(s):  
Lazaros Oreopoulos ◽  
Robert F. Cahalan ◽  
Steven Platnick
Keyword(s):  
Optical Thickness ◽  
Radiative Forcing ◽  
Mean Value ◽  
Time Of Day ◽  
Effective Radius ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Plane Parallel ◽  
Cloud Properties ◽  
Horizontal Inhomogeneity

Abstract The authors present the global plane-parallel shortwave albedo bias of liquid clouds for two months, July 2003 and January 2004. The cloud optical properties necessary to perform the bias calculations come from the operational Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and MODIS Aqua level-3 datasets. These data, along with ancillary surface albedo and atmospheric information consistent with the MODIS retrievals, are inserted into a broadband shortwave radiative transfer model to calculate the fluxes at the atmospheric column boundaries. The plane-parallel homogeneous (PPH) calculations are based on the mean cloud properties, while independent column approximation (ICA) calculations are based either on 1D histograms of optical thickness or joint 2D histograms of optical thickness and effective radius. The (positive) PPH albedo bias is simply the difference between PPH and ICA albedo calculations. Two types of biases are therefore examined: 1) the bias due to the horizontal inhomogeneity of optical thickness alone (the effective radius is set to the grid mean value) and 2) the bias due to simultaneous variations of optical thickness and effective radius as derived from their joint histograms. The authors find that the global bias of albedo (liquid cloud portion of the grid boxes only) is ∼+0.03, which corresponds to roughly 8% of the global liquid cloud albedo and is only modestly sensitive to the inclusion of horizontal effective radius variability and time of day, but depends strongly on season and latitude. This albedo bias translates to ∼3–3.5 W m−2 of bias (stronger negative values) in the diurnally averaged global shortwave cloud radiative forcing, assuming homogeneous conditions for the fraction of the grid box not covered by liquid clouds; zonal values can be as high as 8 W m−2. Finally, the (positive) broadband atmospheric absorptance bias is about an order of magnitude smaller than the albedo bias. The substantial magnitude of the PPH bias underlines the importance of predicting subgrid variability in GCMs and accounting for its effects on cloud–radiation interactions.

scholarly journals Dispersion Aerosol Indirect Effect in Turbulent Clouds: Laboratory Measurements of Effective Radius

2018 ◽  
Vol 45 (19) ◽  
pp. 10,738-10,745 ◽  
Author(s):  
K. K. Chandrakar ◽  
W. Cantrell ◽  
A. B. Kostinski ◽  
R. A. Shaw
Keyword(s):  
Indirect Effect ◽  
Effective Radius ◽  
Laboratory Measurements ◽  
Aerosol Indirect Effect

scholarly journals Combined observational and modeling based study of the aerosol indirect effect

2006 ◽  
Vol 6 (3) ◽  
pp. 3757-3799 ◽  
Author(s):  
T. Storelvmo ◽  
J. E. Kristjansson ◽  
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.

scholarly journals Model intercomparison of indirect aerosol effects

2006 ◽  
Vol 6 (11) ◽  
pp. 3391-3405 ◽  
Author(s):  
J. E. Penner ◽  
J. Quaas ◽  
T. Storelvmo ◽  
T. Takemura ◽  
O. Boucher ◽  
...  
Keyword(s):  
Liquid Water ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
Liquid Water Content ◽  
Cloud Fraction ◽  
Shortwave Radiation ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Forcing ◽  
Indirect Forcing

Abstract. Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol first indirect effect for the first experiment is rather similar, about −0.6 Wm−2 to −0.7 Wm−2. Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Adding an autoconversion scheme that depends on the droplet concentration caused a larger (negative) change in net outgoing shortwave radiation compared to the 1st indirect effect, and the increase varied from only 22% to more than a factor of three. The change in net shortwave forcing in the models due to varying the autoconversion scheme depends on the liquid water content of the clouds as well as their predicted droplet concentrations, and both increases and decreases in the net shortwave forcing can occur when autoconversion schemes are changed. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model "noise". The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models, with values of cloud forcing ranging from −0.3 Wm−2 to −1.4 Wm−2. Thus, this aspect of modeling requires significant improvement in order to improve the prediction of aerosol indirect effects.

scholarly journals Constraining the total aerosol indirect effect in the LMDZ and ECHAM4 GCMs using MODIS satellite data

2006 ◽  
Vol 6 (4) ◽  
pp. 947-955 ◽  
Author(s):  
J. Quaas ◽  
O. Boucher ◽  
U. Lohmann
Keyword(s):  
Satellite Data ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
General Circulation ◽  
Cloud Droplet ◽  
General Circulation Models ◽  
Aerosol Indirect Effect ◽  
Albedo Effect ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. Aerosol indirect effects are considered to be the most uncertain yet important anthropogenic forcing of climate change. The goal of the present study is to reduce this uncertainty by constraining two different general circulation models (LMDZ and ECHAM4) with satellite data. We build a statistical relationship between cloud droplet number concentration and the optical depth of the fine aerosol mode as a measure of the aerosol indirect effect using MODerate Resolution Imaging Spectroradiometer (MODIS) satellite data, and constrain the model parameterizations to match this relationship. We include here "empirical" formulations for the cloud albedo effect as well as parameterizations of the cloud lifetime effect. When fitting the model parameterizations to the satellite data, consistently in both models, the radiative forcing by the combined aerosol indirect effect is reduced considerably, down to −0.5 and −0.3 Wm−2, for LMDZ and ECHAM4, respectively.

scholarly journals The shortwave radiative forcing bias of liquid and ice clouds from MODIS observations

2009 ◽  
Vol 9 (16) ◽  
pp. 5865-5875 ◽  
Author(s):  
L. Oreopoulos ◽  
S. Platnick ◽  
G. Hong ◽  
P. Yang ◽  
R. F. Cahalan
Keyword(s):  
Radiative Transfer ◽  
Optical Thickness ◽  
Radiative Forcing ◽  
Global Climate ◽  
Effective Radius ◽  
Negative Bias ◽  
Ice Clouds ◽  
Plane Parallel ◽  
The Absolute ◽  
The Difference

Abstract. We present an assessment of the plane-parallel bias of the shortwave cloud radiative forcing (SWCRF) of liquid and ice clouds at 1 deg scales using global MODIS (Terra and Aqua) cloud optical property retrievals for four months of the year 2005 representative of the meteorological seasons. The (negative) bias is estimated as the difference of SWCRF calculated using the Plane-Parallel Homogeneous (PPH) approximation and the Independent Column Approximation (ICA). PPH calculations use MODIS-derived gridpoint means while ICA calculations use distributions of cloud optical thickness and effective radius. Assisted by a broadband solar radiative transfer algorithm, we find that the absolute value of global SWCRF bias of liquid clouds at the top of the atmosphere is about 6 W m−2 for MODIS overpass times while the SWCRF bias for ice clouds is smaller in absolute terms by about 0.7 W m−2, but with stronger spatial variability. If effective radius variability is neglected and only optical thickness horizontal variations are accounted for, the absolute SWCRF biases increase by about 0.3–0.4 W m−2 on average. Marine clouds of both phases exhibit greater (more negative) SWCRF biases than continental clouds. Finally, morning (Terra)–afternoon (Aqua) differences in SWCRF bias are much more pronounced for ice clouds, up to about 15% (Aqua producing stronger negative bias) on global scales, with virtually all contribution to the difference coming from land areas. The substantial magnitude of the global SWCRF bias, which for clouds of both phases is collectively about 4 W m−2 for diurnal averages, should be considered a strong motivation for global climate modelers to accelerate efforts linking cloud schemes capable of subgrid condensate variability with appropriate radiative transfer schemes.

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