scholarly journals The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

2010 ◽  
Vol 67 (6) ◽  
pp. 2086-2100 ◽  
Author(s):  
Robin J. Hogan
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Rank Correlation ◽  
Quadrature Point ◽  
Atmospheric Models ◽  
Heating Rates ◽  
Full Spectrum ◽  
Clear Sky ◽  
Different Gases

Abstract The correlated-k-distribution (CKD) method is widely used in the radiative transfer schemes of atmospheric models; it involves dividing the spectrum into a number of bands and then reordering the gaseous absorption coefficients within each one. The fluxes and heating rates for each band may then be computed by discretizing the reordered spectrum into O(10) quadrature points per major gas and performing a pseudomonochromatic radiation calculation for each point. In this paper it is first argued that for clear-sky longwave calculations, sufficient accuracy for most applications can be achieved without the need for bands: reordering may be performed on the entire longwave spectrum. The resulting full-spectrum correlated-k (FSCK) method requires significantly fewer pseudomonochromatic calculations than standard CKD to achieve a given accuracy. The concept is first demonstrated by comparing with line-by-line calculations for an atmosphere containing only water vapor, in which it is shown that the accuracy of heating rate calculations improves approximately in proportion to the square of the number of quadrature points. For more than around 20 points, the root-mean-square error flattens out at around 0.015 K day−1 due to the imperfect rank correlation of absorption spectra at different pressures in the profile. The spectral overlap of m different gases is treated by considering an m-dimensional hypercube where each axis corresponds to the reordered spectrum of one of the gases. This hypercube is then divided up into a number of volumes, each approximated by a single quadrature point, such that the total number of quadrature points is slightly fewer than the sum of the number that would be required to treat each of the gases separately. The gaseous absorptions for each quadrature point are optimized such that they minimize a cost function expressing the deviation of the heating rates and fluxes calculated by the FSCK method from line-by-line calculations for a number of training profiles. This approach is validated for atmospheres containing water vapor, carbon dioxide, and ozone, in which it is found that in the troposphere and most of the stratosphere, heating rate errors of less than 0.2 K day−1 can be achieved using a total of 23 quadrature points, decreasing to less than 0.1 K day−1 for 32 quadrature points. It would be relatively straightforward to extend the method to include other gases.

scholarly journals Full-Spectrum Correlated-k Distribution for Shortwave Atmospheric Radiative Transfer

2004 ◽  
Vol 61 (21) ◽  
pp. 2588-2601 ◽  
Author(s):  
Daniel T. Pawlak ◽  
Eugene E. Clothiaux ◽  
Michael F. Modest ◽  
Jason N. S. Cole
Keyword(s):  
Radiative Transfer ◽  
Source Function ◽  
Computation Time ◽  
Spectral Interval ◽  
Heating Rates ◽  
Full Spectrum ◽  
Solar Source ◽  
Clear Sky ◽  
Spectral Bands ◽  
Atmospheric Radiative Transfer

Abstract The full-spectrum correlated k-distribution (FSCK) method, originally developed for applications in combustion systems, is adapted for use in shortwave atmospheric radiative transfer. By weighting k distributions by the solar source function, the FSCK method eliminates the requirement that the Planck function be constant over a spectral interval. As a consequence, integration may be carried out across the full spectrum as long as the assumption of correlation from one atmospheric level to the next remains valid. Problems with the lack of correlation across the full spectrum are removed by partitioning the spectrum at a wavelength of 0.68 μm into two bands. The resulting two-band approach in the FSCK formalism produces broadband rms clear-sky flux and heating rate errors less than 1% and 6%, respectively, relative to monochromatic calculations and requires only 15 quadrature points per layer, which represents a 60%–90% reduction in computation time relative to other models currently in use. An evaluation of fluxes calculated by the FSCK method in cases with idealized clouds demonstrates that gray cloud scattering in two spectral bands is sufficient to reproduce line-by-line generated fluxes. Two different approaches for modeling absorption by cloud drops were also examined. Explicitly including nongray cloud absorption in solar source function-weighted k distributions results in realistic in-cloud heating rates, although in-cloud heating rates were underpredicted by approximately 8%–12% as compared to line-by-line results. A gray cloud absorption parameter chosen to fit line-by-line results optimally for one cloud or atmospheric profile but applied to different cloud combinations or profiles, also closely approximated line-by-line heating rates.

scholarly journals Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

2020 ◽  
Vol 20 (20) ◽  
pp. 12313-12327
Author(s):  
Manuel Gutleben ◽  
Silke Groß ◽  
Martin Wirth ◽  
Bernhard Mayer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Mineral Dust ◽  
Short Wave ◽  
Radiative Effect ◽  
Mixing Ratios ◽  
Long Wave ◽  
Lidar Measurements ◽  
Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high-spectral-resolution and differential-absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers, increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found at altitudes of highest dust concentration (short wave: +0.5 K d−1; long wave: −0.2 K d−1; net: +0.3 K d−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations, the maximum heating/cooling rates shift to the top of the dust layer (short wave: +2.2 K d−1; long wave: −6.0 to −7.0 K d−1; net: −4.0 to −5.0 K d−1). Additionally, the net heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter-radiation of Saharan air layers is found to reduce cooling at the tops of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 W m−2 at surface level and a maximum of −25 W m−2 at the top of the atmosphere.

scholarly journals A New k-Distribution Scheme for Clear-Sky Radiative Transfer Calculations in Earth’s Atmosphere. Part II: Solar (Shortwave) Heating due to H2O and CO2

2021 ◽  
Author(s):  
Ming-Dah Chou ◽  
Kyu-Tae Lee ◽  
Il-Sung Zo ◽  
Wei-Liang Lee ◽  
Chein-Jung Shiu ◽  
...  
Keyword(s):  
Water Vapor ◽  
Absorption Coefficient ◽  
Solar Heating ◽  
Surface Radiation ◽  
Heating Rates ◽  
Clear Sky ◽  
Distribution Scheme ◽  
The Difference ◽  
Low Pressures ◽  
Maximum Heating

AbstractA new k-distribution scheme without the assumption of the correlation between the absorption coefficients at different pressures is developed for solar heating due to water vapor and CO2. Grouping of spectral points is based on the observation that radiation at spectral points with a large absorption coefficient is quickly absorbed to heat the stratosphere, and the heating below is attributable to the absorption of the solar radiation at the remaining spectral points. By grouping the spectral points with a large absorption coefficient at low pressures, the range of the absorption coefficient of the remaining spectral points is narrowed, and the k-distribution approximation can be accurately applied to compute solar heating in both the stratosphere and troposphere. Grouping of the spectral points is based on the absorption coefficient at a couple of reference pressures where heating is significant. With a total number of 52 spectral groups in the water vapor and CO2 bands, fluxes and heating rates were calculated for various solar zenith angles in some typical and sampled atmospheres in diverse climatic regimes and seasons. The maximum heating rate difference between the k-distribution and line-by-line calculations is < 0.09 K day-1 for water vapor, and < 0.2 K day-1 for CO2. The difference in the surface radiation is ~ 1.4 W m-2 for water vapor and 0.6 W m-2 for CO2, while it could increase to 2.6 W m-2 due to overlapping absorption. These results can be improved by increasing the number of spectral groups at the expense of computational economy.

Using deep learning to emulate and accelerate a radiative-transfer model

2021 ◽  
Author(s):  
Ryan Lagerquist ◽  
David Turner ◽  
Imme Ebert-Uphoff ◽  
Jebb Stewart ◽  
Venita Hagerty
Keyword(s):  
Deep Learning ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Weather Prediction ◽  
Computing Time ◽  
Single Layer ◽  
Radiative Heating ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Heating Rates

AbstractThis paper describes the development of U-net++ models, a type of neural network that performs deep learning, to emulate the shortwave Rapid Radiative-transfer Model (RRTM). The goal is to emulate the RRTM accurately in a small fraction of the computing time, creating a U-net++ that could be used as a parameterization in numerical weather prediction (NWP). Target variables are surface downwelling flux, top-of-atmosphere upwelling flux (), net flux, and a profile of radiative-heating rates. We have devised several ways to make the U-net++ models knowledge-guided, recently identified as a key priority in machine learning (ML) applications to the geosciences. We conduct two experiments to find the best U-net++ configurations. In Experiment 1, we train on non-tropical sites and test on tropical sites, to assess extreme spatial generalization. In Experiment 2, we train on sites from all regions and test on different sites from all regions, with the goal of creating the best possible model for use in NWP. The selected model from Experiment 1 shows impressive skill on the tropical testing sites, except four notable deficiencies: large bias and error for heating rate in the upper stratosphere, unreliable for profiles with single-layer liquid cloud, large heating-rate bias in the mid-troposphere for profiles with multi-layer liquid cloud, and negative bias at lowzenith angles for all flux components and tropospheric heating rates. The selected model from Experiment 2 corrects all but the first deficiency, and both models run ~104 times faster than the RRTM. Our code is available publicly.

Application of the Cumulative Wavenumber Approach for Modeling Radiative Transfer in H2O Under Non-Isothermal and Non-Homogeneous Conditions

2002 ◽  
Author(s):  
Vladimir P. Solovjov ◽  
Brent W. Webb
Keyword(s):  
Heat Transfer ◽  
Water Vapor ◽  
Radiative Transfer ◽  
Radiative Heat ◽  
Radiative Transfer Equation ◽  
Local Spectrum ◽  
Full Spectrum ◽  
Model Predictions ◽  
Spectrum Correlation ◽  
Spectral Database

Recently, the cumulative wavenumber approach was formulated and its viability demonstrated in predictions of radiative heat transfer in high temperature CO2. The approach allows for local spectrum correlation, rather than full-spectrum correlation as commonly done previously. This work reports on the generation of cumulative wavenumber data for H2O, and explores solutions using the cumulative wavenumber approach for water vapor (balance nitrogen) in homogeneous/non-isothermal media, and extends the technique to non-homogeneous/non-isothermal scenarios. Model predictions are compared with rigorous line-by-line benchmark integration of the Radiative Transfer Equation, with the same spectral database (HITEMP) used in both model and line-by-line benchmark predictions.

scholarly journals What Drives the North Atlantic Oscillation’s Temperature Anomaly Pattern? Part II: A Decomposition of the Surface Downward Longwave Radiation Anomalies

2019 ◽  
Vol 77 (1) ◽  
pp. 199-216 ◽  
Author(s):  
Joseph P. Clark ◽  
Steven B. Feldstein
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Water Flux ◽  
Vertical Mixing ◽  
Longwave Radiation ◽  
Temperature Anomalies ◽  
Clear Sky ◽  
The North ◽  
Downward Longwave Radiation ◽  
Thermodynamic Energy

Abstract Radiative transfer calculations are conducted to determine the contribution of temperature and water vapor anomalies toward the surface clear-sky downward longwave radiation (DLR) anomalies of the NAO. These calculations are motivated by the finding that the NAO’s skin temperature anomalies are driven primarily by changes in surface DLR. The clear-sky radiative transfer calculations follow the result that the clear-sky surface DLR anomalies can account for most of the all-sky surface DLR anomalies of the NAO. The results of the radiative transfer calculations prompt an analysis of the thermodynamic energy and total column water (TCW) budget equations, as water vapor and temperature anomalies are found to be equally important drivers of the surface DLR anomalies of the NAO. Composite analysis of the thermodynamic energy equation reveals that the temperature anomalies of the NAO are wind driven: the advection of climatological temperature by the anomalous wind drives the NAO’s temperature anomalies at all levels except for those in the upper troposphere–lower stratosphere where the advection of anomalous temperature by the climatological wind becomes dominant. A similar analysis of the TCW budget reveals that changes in TCW are driven by water flux convergence. In addition to determining the drivers of the temperature and TCW anomalies, the thermodynamic energy and water budget analyses reveal that the decay of the temperature anomalies occurs primarily through vertical mixing, and that of the water anomalies mostly by evaporation minus precipitation.

scholarly journals Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

2020 ◽  
Author(s):  
Manuel Gutleben ◽  
Silke Groß ◽  
Martin Wirth ◽  
Bernhard Mayer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Mineral Dust ◽  
Short Wave ◽  
Radiative Effect ◽  
Mixing Ratios ◽  
Long Wave ◽  
Lidar Measurements ◽  
Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high spectral resolution and differential absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found in altitudes of highest dust concentration (short-wave: +0.5 Kd−1, long-wave: −0.2 Kd−1, net: +0.3 Kd−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations the maximum heating/cooling rates shift to the top of the dust layer (short-wave: +2.2 Kd Kd−1, long-wave: −6.0 to −7.0 Kd−1, net: −5.0 to −4.0 Kd−1). Additionally, the net-heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter radiation of Saharan air layers is found to reduce cooling at the top of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 Wm−2 at surface level and a maximum of −25 Wm−2 at the top of the atmosphere.

Maintenance of Lower Tropospheric Temperature Inversion in the Saharan Air Layer by Dust and Dry Anomaly

2009 ◽  
Vol 22 (19) ◽  
pp. 5149-5162 ◽  
Author(s):  
Sun Wong ◽  
Andrew E. Dessler ◽  
Natalie M. Mahowald ◽  
Ping Yang ◽  
Qian Feng
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Heating Rate ◽  
Temperature Inversion ◽  
Dust Content ◽  
Radiative Heating ◽  
Specific Humidity ◽  
Transfer Model ◽  
Tropospheric Temperature ◽  
Saharan Air Layer

Abstract The role of Saharan dust and dry anomaly in maintaining the temperature inversion in the Saharan air layer (SAL) is investigated. The dust aerosol optical thickness (AOT) in the SAL is inferred from the measurements taken by Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), and the corresponding temperature and specific humidity anomalies are identified using the National Centers for Environmental Prediction (NCEP) data in August–September over the North Atlantic tropical cyclone (TC) main development region (MDR; 10°–20°N, 40°–60°W). The authors also study the SAL simulated in the National Center of Atmospheric Research (NCAR) Community Atmosphere Model, version 3 (CAM3), coupled with dust radiative effect. It is found that higher AOT is associated with warmer and dryer anomalies below 700 hPa, which increases the atmospheric stability. The calculated instantaneous radiative heating anomalies from a radiative transfer model indicate that both the dust and low humidity are essential to maintaining the temperature structure in the SAL against thermal relaxation. At 850 hPa, heating anomalies caused by both the dust and dry anomalies (for AOT &gt; 0.8) are 0.2–0.4 K day−1. The dust heats the atmosphere below 600 hPa, while the dry anomaly cools the atmosphere below 925 hPa, resulting in a peak of heating rate anomaly located at 700–850 hPa. In the eastern Atlantic, dust contributes about 50% of the heating rate anomaly. Westward of 40°W, when the dust content becomes small (AOT &lt; 0.6), the heating rates are more sensitive to the water vapor profile used in the radiative transfer calculation. Retrieving or simulating correct water vapor profiles is essential to the assessment of the SAL heating budgets in regions where the dust content in the SAL is small.

scholarly journals The QME AERI LBLRTM: A Closure Experiment for Downwelling High Spectral Resolution Infrared Radiance

2004 ◽  
Vol 61 (22) ◽  
pp. 2657-2675 ◽  
Author(s):  
D. D. Turner ◽  
D. C. Tobin ◽  
S. A. Clough ◽  
P. D. Brown ◽  
R. G. Ellingson ◽  
...  
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
High Spectral Resolution ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Continuum Absorption ◽  
Clear Sky ◽  
Infrared Radiance ◽  
Wide Range ◽  
Atmospheric State

Abstract Research funded by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program has led to significant improvements in longwave radiative transfer modeling over the last decade. These improvements, which have generally come in small incremental changes, were made primarily in the water vapor self- and foreign-broadened continuum and the water vapor absorption line parameters. These changes, when taken as a whole, result in up to a 6 W m−2 improvement in the modeled clear-sky downwelling longwave radiative flux at the surface and significantly better agreement with spectral observations. This paper provides an overview of the history of ARM with regard to clear-sky longwave radiative transfer, and analyzes remaining related uncertainties in the ARM state-of-the-art Line-by-Line Radiative Transfer Model (LBLRTM). A quality measurement experiment (QME) for the downwelling infrared radiance at the ARM Southern Great Plains site has been ongoing since 1994. This experiment has three objectives: 1) to validate and improve the absorption models and spectral line parameters used in line-by-line radiative transfer models, 2) to assess the ability to define the atmospheric state, and 3) to assess the quality of the radiance observations that serve as ground truth for the model. Analysis of data from 1994 to 1997 made significant contributions to optimizing the QME, but is limited by small but significant uncertainties and deficiencies in the atmospheric state and radiance observations. This paper concentrates on the analysis of QME data from 1998 to 2001, wherein the data have been carefully selected to address the uncertainties in the 1994–97 dataset. Analysis of this newer dataset suggests that the representation of self-broadened water vapor continuum absorption is 3%–8% too strong in the 750–1000 cm−1 region. The dataset also provides information on the accuracy of the self- and foreign-broadened continuum absorption in the 1100–1300 cm−1 region. After accounting for these changes, remaining differences in modeled and observed downwelling clear-sky fluxes are less than 1.5 W m−2 over a wide range of atmospheric states.

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