A fast, flexible, approximate technique for computing radiative transfer in inhomogeneous cloud fields
TL;DR: In this article, a new technique, based on simultaneously sampling cloud state and spectral interval, provides radiative fluxes that are guaranteed to be unbiased with respect to the benchmark Independent Column Approximation and works equally well no matter how cloud structure is specified.
Abstract: [1] Radiative transfer schemes in large-scale models tightly couple assumptions about cloud structure to methods for solving the radiative transfer equation, which makes these schemes inflexible, difficult to extend, and potentially susceptible to biases. A new technique, based on simultaneously sampling cloud state and spectral interval, provides radiative fluxes that are guaranteed to be unbiased with respect to the benchmark Independent Column Approximation and works equally well no matter how cloud structure is specified. Fluxes computed in this way are subject to random, uncorrelated errors that depend on the distribution of cloud optical properties. Seasonal forecasts, however, are not sensitive to this noise, making the method useful in weather and climate prediction models.
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8,699 citations
Cites methods from "A fast, flexible, approximate techn..."
...It incorporates the MCICA (Pincus et al., 2003) for representing subgrid cloud structure and overlap, and the short-wave RRTMG (Iacono et al....
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...It incorporates the MCICA (Pincus et al., 2003) for representing subgrid cloud structure and overlap, and the short-wave RRTMG (Iacono et al., 2008), consistent with the existing use of RRTMG in the long-wave....
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TL;DR: In this article, the AER line-by-line (LBL) models were compared with the RTMIP line-By-line results in the longwave and shortwave for clear sky scenarios previously examined by the radiative transfer model intercomparison project.
Abstract: A primary component of the observed, recent climate change is the radiative forcing from increased concentrations of long-lived greenhouse gases (LLGHGs). Effective simulation of anthropogenic climate change by general circulation models (GCMs) is strongly dependent on the accurate representation of radiative processes associated with water vapor, ozone and LLGHGs. In the context of the increasing application of the Atmospheric and Environmental Research, Inc. (AER) radiation models within the GCM community, their capability to calculate longwave and shortwave radiative forcing for clear sky scenarios previously examined by the radiative transfer model intercomparison project (RTMIP) is presented. Forcing calculations with the AER line-by-line (LBL) models are very consistent with the RTMIP line-by-line results in the longwave and shortwave. The AER broadband models, in all but one case, calculate longwave forcings within a range of -0.20 to 0.23 W m{sup -2} of LBL calculations and shortwave forcings within a range of -0.16 to 0.38 W m{sup -2} of LBL results. These models also perform well at the surface, which RTMIP identified as a level at which GCM radiation models have particular difficulty reproducing LBL fluxes. Heating profile perturbations calculated by the broadband models generally reproduce high-resolution calculations within a few hundredths K d{sup -1} in the troposphere and within 0.15 K d{sup -1} in the peak stratospheric heating near 1 hPa. In most cases, the AER broadband models provide radiative forcing results that are in closer agreement with high 20 resolution calculations than the GCM radiation codes examined by RTMIP, which supports the application of the AER models to climate change research.
3,344 citations
Cites methods from "A fast, flexible, approximate techn..."
...RRTMG_LW and SW with the addition of McICA, the Monte Carlo Independent Column Approximation [Barker et al., 2002; Pincus et al., 2003], which is a statistical technique for representing subgrid-scale cloud variability including cloud overlap....
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...This limitation has been addressed for RRTMG_LW and SW with the addition of McICA, the Monte Carlo Independent Column Approximation [Barker et al., 2002; Pincus et al., 2003], which is a statistical technique for representing subgrid-scale cloud variability including cloud overlap....
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TL;DR: The second version of the NCEP Climate Forecast System (CFSv2) was made operational at the National Center for Environmental Prediction (NCEP) in 2011 as discussed by the authors.
Abstract: The second version of the NCEP Climate Forecast System (CFSv2) was made operational at NCEP in March 2011. This version has upgrades to nearly all aspects of the data assimilation and forecast model components of the system. A coupled reanalysis was made over a 32-yr period (1979–2010), which provided the initial conditions to carry out a comprehensive reforecast over 29 years (1982–2010). This was done to obtain consistent and stable calibrations, as well as skill estimates for the operational subseasonal and seasonal predictions at NCEP with CFSv2. The operational implementation of the full system ensures a continuity of the climate record and provides a valuable up-to-date dataset to study many aspects of predictability on the seasonal and subseasonal scales. Evaluation of the reforecasts show that the CFSv2 increases the length of skillful MJO forecasts from 6 to 17 days (dramatically improving subseasonal forecasts), nearly doubles the skill of seasonal forecasts of 2-m temperatures over the ...
2,520 citations
Cites methods from "A fast, flexible, approximate techn..."
...Because of the exorbitant computational cost of a fully independent column approximation (ICA) method, an alternate approach, which is a Monte Carlo independent column approximation (McICA) (Barker et al. 2002; Pincus et al. 2003), is used in the new CFS model....
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TL;DR: In this article, the effects of aerosols on the climate system are discussed and different approaches how the climatic implications of these effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed.
Abstract: . Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.
2,327 citations
Cites background from "A fast, flexible, approximate techn..."
...transfer through inhomogeneous cloud fields by Pincus et al. (2003). Such a treat-...
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National Center for Atmospheric Research1, Pacific Northwest National Laboratory2, University of Toronto3, Los Alamos National Laboratory4, Cornell University5, University of Wisconsin-Madison6, Lawrence Livermore National Laboratory7, Lawrence Berkeley National Laboratory8, Oak Ridge National Laboratory9, University of Calgary10
TL;DR: The Community Earth System Model (CESM) as discussed by the authors is a community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales, including biogeochemical cycles, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere.
Abstract: The Community Earth System Model (CESM) is a flexible and extensible community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales. This global coupled model significantly extends its predecessor, the Community Climate System Model, by incorporating new Earth system simulation capabilities. These comprise the ability to simulate biogeochemical cycles, including those of carbon and nitrogen, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere. These and other new model capabilities are enabling investigations into a wide range of pressing scientific questions, providing new foresight into possible future climates and increasing our collective knowledge about the behavior and interactions of the Earth system. Simulations with numerous configurations of the CESM have been provided to phase 5 of the Coupled Model Intercomparison Project (CMIP5) and are being analyzed by the broad com...
2,075 citations
References
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TL;DR: In this paper, a stochastic representation of random error associated with parametrized physical processes is described, and its impact in the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS) is discussed.
Abstract: SUMMARY A stochastic representation of random error associated with parametrized physical processes (‘stochastic physics’) is described, and its impact in the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (ECMWF EPS) is discussed. Model random errors associated with physical parametrizations are simulated by multiplying the total parametrized tendencies by a random number sampled from a uniform distribution between 0.5 and 1.5. A number of diagnostics are described and a choice of parameters is made. It is shown how the scheme increases the spread of the ensemble, and improves the skill of the probabilistic prediction of weather parameters such as precipitation. A choice of stochastic parameters is made for operational implementation. The scheme was implemented successfully in the operational ECMWF EPS on 21 October 1998.
1,067 citations
TL;DR: In this paper, a new approach for parameterization of the broadband solar and infrared radiative properties of ice clouds has been developed, which integrates in a coherent manner the δ-four-stream approximation for radiative transfer, the correlated k-distribution method for nongray gaseous absorption, and the scattering and absorption properties of hexagonal ice crystals.
Abstract: A new approach for parameterization of the broadband solar and infrared radiative properties of ice clouds has been developed. This parameterization scheme integrates in a coherent manner the δ-four-stream approximation for radiative transfer, the correlated k-distribution method for nongray gaseous absorption, and the scattering and absorption properties of hexagonal ice crystals. A mean effective size is used, representing an area-weighted mean crystal width, to account for the ice crystal size distribution with respect to radiative calculation. Based on physical principles, the basic single-scattering properties of ice crystals, including the extinction coefficient divided by ice water content single-scattering albedo, and expansion coefficients of the phase function, can be parameterized using third-degree polynomials in terms of the mean effective size. In the development of this parameterization the results computed from a light scattering program that includes a Geometric ray-tracing progr...
907 citations
TL;DR: In this paper, a new parameterization was developed for predicting the shortwave radiative properties of water clouds, suitable for inclusion in general circulation models (GCMs), making use of the simple relationships found by Slingo and Schrecker, giving the three input parameters required to calculate the cloud radiative parameters (the optical depth, single scatter albedo and asymmetry parameter) in terms of the liquid water path and equivalent radius of the drop size distribution.
Abstract: A new parameterization was developed for predicting the shortwave radiative properties of water clouds, suitable for inclusion in general circulation models (GCMs). The parameterization makes use of the simple relationships found by Slingo and Schrecker, giving the three input parameters required to calculate the cloud radiative properties (the optical depth, single scatter albedo and asymmetry parameter) in terms of the liquid water path and equivalent radius of the drop size distribution. The input parameters are then used to derive the cloud radiative properties, using standard two-stream equations for a single layer. The relationships were originally derived for fairly narrow spectral bands but it was found that it is possible to average the coefficients so as to use a much smaller number of bands, without sacrificing accuracy in calculating the cloud radiative properties. This makes the parameterization fast enough to be included in GCMs. The parameterization was programmed into the radiation scheme used in the U.K. Meteorological Office GCM. This scheme and the 24 band Slingo/Schrecker scheme were compared with each other and with observations, using a variety of published datasets. There is good agreement between the two schemes for both cloud albedo and absorption, even when only four spectral bands are employed in the GCM.
624 citations
"A fast, flexible, approximate techn..." refers background in this paper
...The spectral intervals may be thought of as bands [e.g., Slingo, 1989] or as the quasi-monochromatic intervals in a k distribution....
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TL;DR: In this paper, a short climate simulation with a 2D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) is presented.
Abstract: Preliminary results of a short climate simulation with a 2-D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) are presented. The CRM replaces the conventional convective and stratiform cloud parameterizations, and allows for explicit computation of the global cloud fraction distribution for radiation computations. The extreme computational cost of the combined CCSM/CRM model has thus far limited us to a two-month long climate simulation (December-January) using 2.8° × 2.8° resolution. The simulated geographical distributions of the total rainfall, precipitable water, cloud cover, and Earth radiation budget, for the month of January, look very reasonable.
454 citations
TL;DR: In this paper, a parameterization for the horizontal subgrid-scale variability of water vapor and cloud condensate is introduced, which is used to diagnose cloud fraction in the spirit of statistically based cloud cover parameterizations.
Abstract: A parameterization for the horizontal subgrid-scale variability of water vapor and cloud condensate is introduced, which is used to diagnose cloud fraction in the spirit of statistically based cloud cover parameterizations. High-resolution cloud-resolving model data from tropical deep convective scenarios were used to justify the choice of probability density function (PDF). The PDF selected has the advantage of being bounded above and below, avoiding the complications of negative or infinite water mixing ratios, and can give both negatively and positively skewed functions as well as symmetric Gaussian-like bell-shaped curves, without discrete transitions, and is mathematically straightforward to implement. A development from previous statistical parameterizations is that the new scheme is prognostic, with processes such as deep convection, turbulence, and microphysics directly affecting the distribution of higher-order moments of variance and skewness. The scheme is able to represent the growth and decay of cirrus cloud decks and also the creation of cloud in clear sky or breakup of an overcast cloud deck by boundary layer turbulence. After introducing the mathematical framework, results using the parameterization in a climate model are shown to illustrate its behavior. The parameterization is shown to reduce cloud cover biases almost globally, with a marked improvement in the stratocumulus regions in the eastern Pacific and Atlantic Oceans.
393 citations
"A fast, flexible, approximate techn..." refers background in this paper
...Statistical cloud schemes [e.g., Tompkins, 2002] could generate columns consistent with the probability distribution of condensate predicted within each model layer, with overlap relationships incorporated by making the probability of condensate values for one layer conditional on other layers....
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...…impacts radiative fluxes as well as microphysical process rates [Pincus and Klein, 2000], so cloud schemes are now emerging that address this structure either parametrically [Cusack et al., 1999; Tompkins, 2002] or explicitly [Grabowski and Smolarkiewicz, 1999; Khairoutdinov and Randall, 2001]....
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