Impact of Multiple Scattering on Longwave Radiative Transfer Involving Clouds

General circulation models (GCMs) are extensively used to estimate the influence of clouds on the global energy budget and other aspects of climate. Because radiative transfer computations involved in GCMs are costly, it is typical to consider only absorption but not scattering by clouds in longwave (LW) spectral bands. In this study, the flux and heating rate biases due to neglecting the scattering of LW radiation by clouds are quantified by using advanced cloud optical property models, and satellite data from Cloudâ Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, Clouds and the Earth’s Radiant Energy System (CERES), and Moderate Resolution Imaging Spectrometer (MODIS) merged products (CCCM). From the products, information about the atmosphere and clouds (microphysical and buck optical properties, and top and base heights) is used to simulate fluxes and heating rates. Oneâ year global simulations for 2010 show that the LW scattering decreases topâ ofâ atmosphere (TOA) upward flux and increases surface downward flux by 2.6 and 1.2 W/m2, respectively, or approximately 10% and 5% of the TOA and surface LW cloud radiative effect, respectively. Regional TOA upward flux biases are as much as 5% of global averaged outgoing longwave radiation (OLR). LW scattering causes approximately 0.018 K/d cooling at the tropopause and about 0.028 K/d heating at the surface. Furthermore, over 40% of the total OLR bias for ice clouds is observed in 350â 500 cmâ 1. Overall, the radiative effects associated with neglecting LW scattering are comparable to the counterpart due to doubling atmospheric CO2 under clearâ sky conditions.Key PointsGlobal impacts of LW scattering are evaluated by using high spatial resolution satelliteâ derived cloud properties and top and base heightsOmitting cloud LW scattering increases annual mean TOA upward flux by 2.6 W/m2 and decreases annual mean surface downward flux by 1.2 W/m2Including LW scattering of clouds in simulations cools the tropopause approximately 0.018 K/d and heats the surface about 0.028 K/dPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141388/1/jame20524_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141388/2/jame20524.pd

Improvement and Application of Atmospheric Radiative Transfer Models for Prediction of the Climatic Effects of Aerosol

This paper presents a radiative transfer model that has been developed to accurately predict the atmospheric radiant flux in both the infrared and the solar spectrum with a minimum of computational effort. The model is designed to be included in numerical climate models. To assess the accuracy of the model, the results are compared to other more detailed models for several standard cases in the solar and thermal spectrum. As the thermal spectrum has been treated in other publications, we focus here on the solar part of the spectrum. We perform several example calculations focussing on the question of absorption of solar radiation by gases and aerosols

Integrable N = 2 Landau-Ginzburg Theories from Quotients of Fusion Rings

The discovery of integrable $N=2$ supersymmetric Landau-Ginzburg theories whose chiral rings are fusion rings suggests a close connection between fusion rings, the related Landau-Ginzburg superpotentials, and $N=2$ quantum integrability. We examine this connection by finding the natural $SO(N)_K$ analogue of the construction that produced the superpotentials with $Sp(N)_K$ and $SU(N)_K$ fusion rings as chiral rings. The chiral rings of the new superpotentials are not directly the fusion rings of any conformal field theory, although they are natural quotients of the tensor subring of the $SO(N)_K$ fusion ring. The new superpotentials yield solvable (twisted $N=2$) topological field theories. We obtain the integer-valued correlation functions as sums of $SO(N)_K$ Verlinde dimensions by expressing the correlators as fusion residues. The $SO(2n+1)_{2k+1}$ and $SO(2k+1)_{2n+1}$ related topological Landau-Ginzburg theories are isomorphic, despite being defined via quite different superpotentials.Comment: 34 pages, BRX-TH-34

Radiative Forcing by Long-Lived Greenhouse Gases: Calculations with the AER Radiative Transfer Models

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

The Continual Intercomparison of Radiation Codes: Results from Phase I

The computer codes that calculate the energy budget of solar and thermal radiation in Global Climate Models (GCMs), our most advanced tools for predicting climate change, have to be computationally efficient in order to not impose undue computational burden to climate simulations. By using approximations to gain execution speed, these codes sacrifice accuracy compared to more accurate, but also much slower, alternatives. International efforts to evaluate the approximate schemes have taken place in the past, but they have suffered from the drawback that the accurate standards were not validated themselves for performance. The manuscript summarizes the main results of the first phase of an effort called "Continual Intercomparison of Radiation Codes" (CIRC) where the cases chosen to evaluate the approximate models are based on observations and where we have ensured that the accurate models perform well when compared to solar and thermal radiation measurements. The effort is endorsed by international organizations such as the GEWEX Radiation Panel and the International Radiation Commission and has a dedicated website (i.e., http://circ.gsfc.nasa.gov) where interested scientists can freely download data and obtain more information about the effort's modus operandi and objectives. In a paper published in the March 2010 issue of the Bulletin of the American Meteorological Society only a brief overview of CIRC was provided with some sample results. In this paper the analysis of submissions of 11 solar and 13 thermal infrared codes relative to accurate reference calculations obtained by so-called "line-by-line" radiation codes is much more detailed. We demonstrate that, while performance of the approximate codes continues to improve, significant issues still remain to be addressed for satisfactory performance within GCMs. We hope that by identifying and quantifying shortcomings, the paper will help establish performance standards to objectively assess radiation code quality, and will guide the development of future phases of CIR

Absorption Coefficient (ABSCO) Tables for the Orbiting Carbon Observatories: Version 5.1

The accuracy of atmospheric trace gas retrievals depends directly on the accuracy of the molecular absorption model used within the retrieval algorithm. For remote sensing of well-mixed gases, such as carbon dioxide (CO₂), where the atmospheric variability is small compared to the background, the quality of the molecular absorption model is key. Recent updates to oxygen (O₂) absorption coefficients (ABSCO) for the 0.76 μm A-band and the water vapor (H₂O) continuum model within the 1.6 μm and 2.06 μm CO₂ bands used within the Orbiting Carbon Observatory (OCO-2 and OCO-3) algorithm are described here. Updates in the O₂ A-band involve the inclusion of new laboratory measurements within multispectrum fits to improve relative consistency between O₂ line shapes and collision-induced absorption (CIA). The H₂O continuum model has been updated to MTCKD v3.2, which has benefited from information from a range of laboratory studies relative to the model utilized in the previous ABSCO version. Impacts of these spectroscopy updates have been evaluated against ground-based atmospheric spectra from the Total Carbon Column Observing Network (TCCON) and within the framework of the OCO-2 algorithm, using OCO-2 soundings covering a range of atmospheric and surface conditions. The updated absorption coefficients (ABSCO version 5.1) are found to offer improved fitting residuals and reduced biases in retrieved surface pressure relative to the previous version (ABSCO v5.0) used within B8 and B9 of the OCO-2 retrieval algorithm and have been adopted for the OCO B10 Level 2 algorithm

Absorption Coefficient (ABSCO) Tables for the Orbiting Carbon Observatories: Version 5.1

The accuracy of atmospheric trace gas retrievals depends directly on the accuracy of the molecular absorption model used within the retrieval algorithm. For remote sensing of well-mixed gases, such as carbon dioxide (CO₂), where the atmospheric variability is small compared to the background, the quality of the molecular absorption model is key. Recent updates to oxygen (O₂) absorption coefficients (ABSCO) for the 0.76 μm A-band and the water vapor (H₂O) continuum model within the 1.6 μm and 2.06 μm CO₂ bands used within the Orbiting Carbon Observatory (OCO-2 and OCO-3) algorithm are described here. Updates in the O₂ A-band involve the inclusion of new laboratory measurements within multispectrum fits to improve relative consistency between O₂ line shapes and collision-induced absorption (CIA). The H₂O continuum model has been updated to MTCKD v3.2, which has benefited from information from a range of laboratory studies relative to the model utilized in the previous ABSCO version. Impacts of these spectroscopy updates have been evaluated against ground-based atmospheric spectra from the Total Carbon Column Observing Network (TCCON) and within the framework of the OCO-2 algorithm, using OCO-2 soundings covering a range of atmospheric and surface conditions. The updated absorption coefficients (ABSCO version 5.1) are found to offer improved fitting residuals and reduced biases in retrieved surface pressure relative to the previous version (ABSCO v5.0) used within B8 and B9 of the OCO-2 retrieval algorithm and have been adopted for the OCO B10 Level 2 algorithm