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1
Cathey, H. M. "Scientific balloon effective radiative properties." Advances in Space Research 21, no. 7 (1998): 979–82. http://dx.doi.org/10.1016/s0273-1177(97)01084-3.
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Zhang, Chongshan, Abraham Kribus, and Rami Ben-Zvi. "Effective Radiative Properties of a Cylinder Array." Journal of Heat Transfer 124, no. 1 (2001): 198–200. http://dx.doi.org/10.1115/1.1423317.
Testo completoAbstract (sommario):
Fully anisotropic problems are found where the radiative interaction is due to small-scale elements that lack spherical symmetry, for example: fibrous insulation, finned heat sinks, plant canopies, and some solar energy absorbers. We present the effective bulk optical properties of a PM composed of small-scale opaque cylinders. The properties are derived from data generated by detailed Monte-Carlo numerical experiments. The data reduction procedure is relatively simple and does not require a full solution and optimization of the Radiative Transfer Equation. Benchmark cases are presented, comparing an exact solution (with geometric detail of the cylinder array) and an approximate solution using a continuous PM model with the effective volumetric properties.
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Kishore, Ravi Anant, Chuck Booten, and Sajith Wijesuriya. "Effective properties of semitransparent radiative cooling materials with spectrally variable properties." Applied Thermal Engineering 205 (March 2022): 118048. http://dx.doi.org/10.1016/j.applthermaleng.2022.118048.
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Lee, Wan-Ho, and Richard C. J. Somerville. "Effects of alternative cloud radiation parameterizations in a general circulation model." Annales Geophysicae 14, no. 1 (1996): 107–14. http://dx.doi.org/10.1007/s00585-996-0107-6.
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Abstract. Using the National Center for Atmospheric Research (NCAR) general circulation model (CCM2), a suite of alternative cloud radiation parameterizations has been tested. Our methodology relies on perpetual July integrations driven by ±2 K sea surface temperature forcing. The tested parameterizations include relative humidity based clouds and versions of schemes involving a prognostic cloud water budget. We are especially interested in testing the effect of cloud optical thickness feedbacks on global climate sensitivity. All schemes exhibit negative cloud radiation feedbacks, i.e., cloud moderates the global warming. However, these negative net cloud radiation feedbacks consist of quite different shortwave and longwave components between a scheme with interactive cloud radiative properties and several schemes with specified cloud water paths. An increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn negative shortwave feedbacks for the interactive radiative scheme, while a decrease in cloud amount leads to a positive shortwave feedback for the other schemes. For the longwave feedbacks, a decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while no distinct changes in effective high cloudiness and the resulting feedback are exhibited for the scheme with interactive radiative properties. The resulting magnitude of negative net cloud radiation feed-back is largest for the scheme with interactive radiative properties. Even though the simulated values of cloud radiative forcing for the present climate using this method differ most from the observational data, the approach shows great promise for the future.
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Bouraoui, Chaima, and Fayçal Ben Nejma. "Identification of the Effective Radiative Properties of Cylindrical Packed Bed Porous Media." WSEAS TRANSACTIONS ON HEAT AND MASS TRANSFER 19 (January 26, 2024): 1–17. http://dx.doi.org/10.37394/232012.2024.19.1.
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Understanding radiative exchange in a porous medium is a crucial step that can provide significant insights and improvements in its characteristics, enhancing its practical utility across various industrial applications. In this paper, a numerical model, utilizing the finite element method (FEM), was developed to predict the radiative transfer between a diffusely/specularly reflecting cylindrical packed bed porous medium and a plane heating surface. Four different structures of the medium were suggested to examine the effect of the particles ‘disposition on the radiative properties of the medium. The assessment of normalized flux distribution enables the computation of effective radiative properties including reflectivity, transmissivity, and absorptivity for particles exhibiting diffuse and specular reflection. The results underscore the significant influence of particle arrangement on media properties. The structure of the second model allowed for the attainment of an opaque surface from the first layer. Meaningful correlations can be established from the presented curves, offering a streamlined and accurate method for determining effective radiative property coefficients based on emissivity in future model applications.
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Lee, Siu-Chun, Susan White, and Jan A. Grzesik. "Effective radiative properties of fibrous composites containing spherical particles." Journal of Thermophysics and Heat Transfer 8, no. 3 (1994): 400–405. http://dx.doi.org/10.2514/3.556.
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Zelinka, Mark D., Christopher J. Smith, Yi Qin, and Karl E. Taylor. "Comparison of methods to estimate aerosol effective radiative forcings in climate models." Atmospheric Chemistry and Physics 23, no. 15 (2023): 8879–98. http://dx.doi.org/10.5194/acp-23-8879-2023.
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Abstract. Uncertainty in the effective radiative forcing (ERF) of climate primarily arises from the unknown contribution of aerosols, which impact radiative fluxes directly and through modifying cloud properties. Climate model simulations with fixed sea surface temperatures but perturbed atmospheric aerosol loadings allow for an estimate of how strongly the planet's radiative energy budget has been perturbed by the increase in aerosols since pre-industrial times. The approximate partial radiative perturbation (APRP) technique further decomposes the contributions to the direct forcing due to aerosol scattering and absorption and to the indirect forcing due to aerosol-induced changes in cloud scattering, amount, and absorption, as well as the effects of aerosols on surface albedo. Here we evaluate previously published APRP-derived estimates of aerosol effective radiative forcings from these simulations conducted in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and find that they are biased as a result of two large coding errors that – in most cases – fortuitously compensate. The most notable exception is the direct radiative forcing from absorbing aerosols, which is more than 40 % larger averaged across CMIP6 models in the present study. Correcting these biases eliminates the residuals and leads to better agreement with benchmark estimates derived from double calls to the radiation code. The APRP method – when properly implemented – remains a highly accurate and efficient technique for diagnosing aerosol ERF in cases where double radiation calls are not available, and in all cases it provides quantification of the individual contributors to the ERF that are highly useful but not otherwise available.
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Yeh, H. Y. M., N. Prasad, and R. F. Adler. "Tabulation of Mie properties for an effective microwave radiative model." Meteorology and Atmospheric Physics 42, no. 2 (1990): 105–12. http://dx.doi.org/10.1007/bf01041758.
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MARSHALL, T. J., and D. G. C. MCKEON. "RADIATIVE PROPERTIES OF THE STUECKELBERG MECHANISM." International Journal of Modern Physics A 23, no. 05 (2008): 741–48. http://dx.doi.org/10.1142/s0217751x08039499.
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We examine the mechanism for generating a mass for a U(1) vector field introduced by Stueckelberg. First, it is shown that renormalization of the vector mass is identical to the renormalization of the vector field on account of gauge invariance. We then consider how the vector mass affects the effective potential in scalar quantum electrodynamics at one-loop order. The possibility of extending this mechanism to couple, in a gauge invariant way, a charged vector field to the photon is discussed.
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Jenblat, S. S., and O. V. Volkova. "Estimation of multi-layer coating efficiency for passive radiative cooling." Omsk Scientific Bulletin. Series Aviation-Rocket and Power Engineering 5, no. 2 (2021): 37–46. http://dx.doi.org/10.25206/2588-0373-2021-5-2-37-46.
Testo completoAbstract (sommario):
Passive radiative cooling is a promising direction in energy conservation and environmental protection. One of the ways to increase the efficiency of radiative cooling systems is the use of multi-layer coatings. In recent years, several novel materials with high emissivity have been proposed, which allow the creation of radiators that provide an average daily cooling power of approximately 100 W/m2 during daytime. Based on the developed mathematical model, the optical properties of the multi-layer coating for the radiative cooling system were evaluated by the Transfer Matrix Method and the effectiveness of radiative cooling was determined due to the use of the multi-layer coating in the climatic conditions of Syria (Latakia). The results of modeling the atmospheric transmittance in the summer months in Syria (Latakia) are presented. The developed mathematical model, methods for modeling atmospheric transmittance, calculating solar radiation, and evaluating the optical properties of multi-layer coating, allow determining an effective multi-layer coating for radiative cooling systems in any climatic conditions
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Finger, Fanny, Frank Werner, Marcus Klingebiel, et al. "Spectral optical layer properties of cirrus from collocated airborne measurements and simulations." Atmospheric Chemistry and Physics 16, no. 12 (2016): 7681–93. http://dx.doi.org/10.5194/acp-16-7681-2016.
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Abstract. Spectral upward and downward solar irradiances from vertically collocated measurements above and below a cirrus layer are used to derive cirrus optical layer properties such as spectral transmissivity, absorptivity, reflectivity, and cloud top albedo. The radiation measurements are complemented by in situ cirrus crystal size distribution measurements and radiative transfer simulations based on the microphysical data. The close collocation of the radiative and microphysical measurements, above, beneath, and inside the cirrus, is accomplished by using a research aircraft (Learjet 35A) in tandem with the towed sensor platform AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected from two field campaigns over the North Sea and the Baltic Sea in spring and late summer 2013. One measurement flight over the North Sea proved to be exemplary, and as such the results are used to illustrate the benefits of collocated sampling. The radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius reff, and optical thickness τ on cirrus spectral optical layer properties. Furthermore, the radiative effects of low-level, liquid water (warm) clouds as frequently observed beneath the cirrus are evaluated. They may cause changes in the radiative forcing of the cirrus by a factor of 2. When low-level clouds below the cirrus are not taken into account, the radiative cooling effect (caused by reflection of solar radiation) due to the cirrus in the solar (shortwave) spectral range is significantly overestimated.
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Szczap, Frédéric, Harumi Isaka, Marcel Saute, Bernard Guillemet, and Andrey Ioltukhovski. "Effective radiative properties of bounded cascade absorbing clouds: Definition of an effective single-scattering albedo." Journal of Geophysical Research: Atmospheres 105, no. D16 (2000): 20635–48. http://dx.doi.org/10.1029/2000jd900145.
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Chen, Y. B., Z. M. Zhang, and P. J. Timans. "Radiative Properties of Patterned Wafers With Nanoscale Linewidth." Journal of Heat Transfer 129, no. 1 (2006): 79–90. http://dx.doi.org/10.1115/1.2401201.
Testo completoAbstract (sommario):
Abstract Temperature nonuniformity is a critical problem in rapid thermal processing (RTP) of wafers because it leads to uneven diffusion of implanted dopants and introduces thermal stress. One cause of the problem is nonuniform absorption of thermal radiation, especially in patterned wafers, where the optical properties vary across the wafer surface. Recent developments in RTP have led to the use of millisecond-duration heating cycle, which is too short for thermal diffusion to even out the temperature distribution. The feature size is already below 100nm and is smaller than the wavelength (200-1000nm) of the flash-lamp radiation. Little is known to the spectral distribution of the absorbed energy for different patterning structures. This paper presents a parametric study of the radiative properties of patterned wafers with the smallest feature dimension down to 30nm, considering the effects of temperature, wavelength, polarization, and angle of incidence. The rigorous coupled wave analysis is employed to obtain numerical solutions of the Maxwell equations and to assess the applicability of the method of homogenization based on effective medium formulations.
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Ganbold, Gurjav. "Charmonium radiative transitions, meson and glueball particle properties with the effective strong coupling." EPJ Web of Conferences 204 (2019): 08002. http://dx.doi.org/10.1051/epjconf/201920408002.
Testo completoAbstract (sommario):
The particle properties of conventional mesons and scalar glueball, radiative transitions of charmonium excited states χcJ (J = 0, 1, 2) are studied in the framework of relativistic quark models with infrared confinement by taking into account the mass dependence of the effective strong coupling. A specific behaviour of the mass-dependent strong coupling with a freezing point αs (0) = 1.032 has been revealed. The spectrum and leptonic (weak) decay constants of conventional mesons have been calculated in good agreement with the latest experimental data. New estimates on the scalar glueball mass, ’radius’ and gluon condensate value have been obtained. Dominant radiative transitions of the charmonium orbital excitations χcJ → J/ψ + γ have been studied and the partial decay widths have been estimated with reasonable accuracy.
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Borges dos Santos, Marcelo, Luís Mauro Moura, and Dominique Baillis. "Identification of the Radiative Parameters-Albedo and Optical Thickness—Of the Juncus maritimus Fiber." Materials 16, no. 5 (2023): 1891. http://dx.doi.org/10.3390/ma16051891.
Testo completoAbstract (sommario):
The present work aims to characterize the radiative thermal properties albedo and optical thickness of Juncus maritimus fibers using a FTIR spectrometer. Measurements of normal/directional transmittance and normal and hemispherical reflectance are performed. The numerical determination of the radiative properties is conducted through the computational treatment of the Radiative Transfer Equation (RTE) using the Discrete Ordinate Method (DOM), together with the inverse method, which is done through Gauss linearization. As it is a non-linear system, iterative calculations are necessary, which demand a significant computational cost, and, to optimize this problem, the Neumann method is used for the numerical determination of the parameters. These radiative properties are useful to quantify the radiative effective conductivity.
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Li, Ming, Husi Letu, Yiran Peng, et al. "Investigation of ice cloud modeling capabilities for the irregularly shaped Voronoi ice scattering models in climate simulations." Atmospheric Chemistry and Physics 22, no. 7 (2022): 4809–25. http://dx.doi.org/10.5194/acp-22-4809-2022.
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Abstract. Both weather–climate models and ice cloud remote sensing applications need to obtain effective ice crystal scattering (ICS) properties and the parameterization scheme. An irregularly shaped Voronoi ICS model has been suggested to be effective in remote sensing applications for several satellite programs, e.g., Himawari-8, GCOM-C (Global Change Observation Mission–Climate) and EarthCARE (Earth Cloud Aerosol and Radiation Explorer). As continuation work of Letu et al. (2016), an ice cloud optical property parameterization scheme (Voronoi scheme) of the Voronoi ICS model is employed in the Community Integrated Earth System Model (CIESM) to simulate the optical and radiative properties of ice clouds. We utilized the single-scattering properties (extinction efficiency, single-scattering albedo and asymmetry factor) of the Voronoi model from the ultraviolet to the infrared, combined with 14 408 particle size distributions obtained from aircraft measurements to complete the Voronoi scheme. The Voronoi scheme and existing schemes (Fu, Mitchell, Yi and Baum-yang05) are applied to the CIESM to simulate 10-year global cloud radiative effects during 2001–2010. Simulated globally averaged cloud radiative forcings at the top of the atmosphere (TOA) for Voronoi and the other four existing schemes are compared to the Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (EBAF) product. The results show that the differences in shortwave and longwave globally averaged cloud radiative forcing at the TOA between the Voronoi scheme simulations and EBAF products are 1.1 % and 1.4 %, which are lower than those of the other four schemes. Particularly for regions (from 30∘ S to 30∘ N) where ice clouds occur frequently, the Voronoi scheme provides the closest match with EBAF products compared with the other four existing schemes. The results in this study fully demonstrated the effectiveness of the Voronoi ICS model in the simulation of the radiative properties of ice clouds in the climate model.
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Grandey, Benjamin S., Daniel Rothenberg, Alexander Avramov, et al. "Effective radiative forcing in the aerosol–climate model CAM5.3-MARC-ARG." Atmospheric Chemistry and Physics 18, no. 21 (2018): 15783–810. http://dx.doi.org/10.5194/acp-18-15783-2018.
Testo completoAbstract (sommario):
Abstract. We quantify the effective radiative forcing (ERF) of anthropogenic aerosols modelled by the aerosol–climate model CAM5.3-MARC-ARG. CAM5.3-MARC-ARG is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC). CAM5.3-MARC-ARG uses the ARG aerosol-activation scheme, consistent with the default configuration of CAM5.3. We compute differences between simulations using year-1850 aerosol emissions and simulations using year-2000 aerosol emissions in order to assess the radiative effects of anthropogenic aerosols. We compare the aerosol lifetimes, aerosol column burdens, cloud properties, and radiative effects produced by CAM5.3-MARC-ARG with those produced by the default configuration of CAM5.3, which uses the modal aerosol module with three log-normal modes (MAM3), and a configuration using the modal aerosol module with seven log-normal modes (MAM7). Compared with MAM3 and MAM7, we find that MARC produces stronger cooling via the direct radiative effect, the shortwave cloud radiative effect, and the surface albedo radiative effect; similarly, MARC produces stronger warming via the longwave cloud radiative effect. Overall, MARC produces a global mean net ERF of -1.79±0.03 W m−2, which is stronger than the global mean net ERF of -1.57±0.04 W m−2 produced by MAM3 and -1.53±0.04 W m−2 produced by MAM7. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the shortwave cloud radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.
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Huang, Xianglei, Xiuhong Chen, Gerald L. Potter, et al. "A Global Climatology of Outgoing Longwave Spectral Cloud Radiative Effect and Associated Effective Cloud Properties." Journal of Climate 27, no. 19 (2014): 7475–92. http://dx.doi.org/10.1175/jcli-d-13-00663.1.
Testo completoAbstract (sommario):
Abstract Longwave (LW) spectral flux and cloud radiative effect (CRE) are important for understanding the earth’s radiation budget and cloud–radiation interaction. Here, the authors extend their previous algorithms to collocated Atmospheric Infrared Sounder (AIRS) and Cloud and the Earth’s Radiant Energy System (CERES) observations over the entire globe and show that the algorithms yield consistently good performances for measurements over both land and ocean. As a result, the authors are able to derive spectral flux and CRE at 10-cm−1 intervals over the entire LW spectrum from all currently available collocated AIRS and CERES observations. Using this multiyear dataset, they delineate the climatology of spectral CRE, including the far IR, over the entire globe as well as in different climate zones. Furthermore, the authors define two quantities, IR-effective cloud-top height (CTHeff) and cloud amount (CAeff), based on the monthly-mean spectral (or band by band) CRE. Comparisons with cloud fields retrieved by the CERES–Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm indicate that, under many circumstances, the CTHeff and CAeff can be related to the physical retrievals of CTH and CA and thus can enhance understandings of model deficiencies in LW radiation budgets and cloud fields. Using simulations from the GFDL global atmosphere model, version 2 (AM2); NASA’s Goddard Earth Observing System, version 5 (GEOS-5); and Environment Canada’s Canadian Centre for Climate Modelling and Analysis (CCCma) Fourth Generation Canadian Atmospheric General Circulation Model (CanAM4) as case studies, the authors further demonstrate the merits of the CTHeff and CAeff concepts in providing insights on global climate model evaluations that cannot be obtained solely from broadband LW flux and CRE comparisons.
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Brenguier, Jean-Louis, Hanna Pawlowska, Lothar Schüller, Rene Preusker, Jürgen Fischer, and Yves Fouquart. "Radiative Properties of Boundary Layer Clouds: Droplet Effective Radius versus Number Concentration." Journal of the Atmospheric Sciences 57, no. 6 (2000): 803–21. http://dx.doi.org/10.1175/1520-0469(2000)057<0803:rpoblc>2.0.co;2.
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Nisipeanu, E., and P. D. Jones. "Identification of the effective radiative properties of a hot, thick, porous medium." Journal of Quantitative Spectroscopy and Radiative Transfer 60, no. 1 (1998): 85–96. http://dx.doi.org/10.1016/s0022-4073(97)00156-8.
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Moser, Daniel, Sreekanth Pannala, and Jayathi Murthy. "Computation of Effective Radiative Properties of Powders for Selective Laser Sintering Simulations." JOM 67, no. 5 (2015): 1194–202. http://dx.doi.org/10.1007/s11837-015-1386-8.
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Kotey, Nathan A., John L. Wright, and Michael R. Collins. "A method for determining the effective longwave radiative properties of pleated draperies." HVAC&R Research 17, no. 5 (2011): 660–69. http://dx.doi.org/10.1080/10789669.2011.591257.
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Wagner, T., S. Beirle, T. Deutschmann, M. Grzegorski, and U. Platt. "Dependence of cloud properties derived from spectrally resolved visible satellite observations on surface temperature." Atmospheric Chemistry and Physics 8, no. 9 (2008): 2299–312. http://dx.doi.org/10.5194/acp-8-2299-2008.
Testo completoAbstract (sommario):
Abstract. Cloud climate feedback constitutes the most important uncertainty in climate modelling, and currently even its sign is still unknown. In the recently published report of the intergovernmental panel on climate change (IPCC), 6 out of 20 climate models showed a positive and 14 a negative cloud radiative feedback in a doubled CO2 scenario. The radiative budget of clouds has also been investigated by experimental methods, especially by studying the relation of satellite observed broad band shortwave and longwave radiation to sea surface temperature. Here we present a new method for the investigation of the dependence of cloud properties on temperature changes, derived from spectrally resolved satellite observations in the visible spectral range. Our study differs from previous investigations in three important ways: first, we directly extract cloud properties (effective cloud fraction and effective cloud top height) and relate them to surface temperature. Second, we retrieve the cloud altitude from the atmospheric O2 absorption instead from thermal IR radiation. Third, our correlation analysis is performed using 7.5 years of global monthly anomalies (with respect to the average of the same month for all years). For most parts of the globe (except the tropics) we find a negative correlation of effective cloud fraction versus surface-near temperature. In contrast, for the effective cloud top height a positive correlation is found for almost the whole globe. Both findings might serve as an indicator for an overall positive cloud radiative feedback. Another peculiarity of our study is that the cloud-temperature relationships are determined for fixed locations (instead to spatial variations over selected areas) and are based on the "natural" variability over several years (instead the anomaly for a strong El-Nino event). From a detailed comparison to cloud properties from the International Satellite Cloud Climatology Project (ISCCP), in general good agreement is found. However, also systematic differences occurred indicating that our results provide independent and complementary information on cloud properties. Climate models should thus aim to reproduce our findings. Recommendations for the development of a "processor" to convert model results into the cloud sensitive quantities observed by the satellite are given.
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Zhukovsky, Vladimir Ch. "Radiative Effects in Low-Dimensional Effective Fermion Field Theory with Compactification." Symmetry 15, no. 10 (2023): 1867. http://dx.doi.org/10.3390/sym15101867.
Testo completoAbstract (sommario):
The introduction of branes immersed in the space-times of higher dimensions revealed itself to be a useful instrument for the study of high-dimensional models in quantum field theory. Moreover, low-dimensional quantum field theories represent an especially interesting class of models in physics due to their unique properties and renormalizability when interactions are treated perturbatively. The advantages of both approaches can be combined in a model for a low-dimensional brane immersed in the usual tetradimensional Minkowski space-time, the properties of which are relatively well known. This approach can be used for the study of systems like graphene and carbon nanotubes. In the present work, we present an effective model for nanotubes based on the Lagrangian obtained from a tight-binding model for graphene. The induced current, appearing azimuthally in the presence of a magnetic flux through the tube section (Aharonov–Bohm effect), will be derived. A reduced Lagragian for photons confined on the tube surface, obtained from the literature, is included in the last part of the work to threat perturbative corrections to the induced current.
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Yi, Bingqi, Ping Yang, Bryan A. Baum, et al. "Influence of Ice Particle Surface Roughening on the Global Cloud Radiative Effect." Journal of the Atmospheric Sciences 70, no. 9 (2013): 2794–807. http://dx.doi.org/10.1175/jas-d-13-020.1.
Testo completoAbstract (sommario):
Abstract Ice clouds influence the climate system by changing the radiation budget and large-scale circulation. Therefore, climate models need to have an accurate representation of ice clouds and their radiative effects. In this paper, new broadband parameterizations for ice cloud bulk scattering properties are developed for severely roughened ice particles. The parameterizations are based on a general habit mixture that includes nine habits (droxtals, hollow/solid columns, plates, solid/hollow bullet rosettes, aggregate of solid columns, and small/large aggregates of plates). The scattering properties for these individual habits incorporate recent advances in light-scattering computations. The influence of ice particle surface roughness on the ice cloud radiative effect is determined through simulations with the Fu–Liou and the GCM version of the Rapid Radiative Transfer Model (RRTMG) codes and the National Center for Atmospheric Research Community Atmosphere Model (CAM, version 5.1). The differences in shortwave (SW) and longwave (LW) radiative effect at both the top of the atmosphere and the surface are determined for smooth and severely roughened ice particles. While the influence of particle roughening on the single-scattering properties is negligible in the LW, the results indicate that ice crystal roughness can change the SW forcing locally by more than 10 W m−2 over a range of effective diameters. The global-averaged SW cloud radiative effect due to ice particle surface roughness is estimated to be roughly 1–2 W m−2. The CAM results indicate that ice particle roughening can result in a large regional SW radiative effect and a small but nonnegligible increase in the global LW cloud radiative effect.
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Lindfors, A. V., N. Kouremeti, A. Arola, S. Kazadzis, A. F. Bais, and A. Laaksonen. "Effective aerosol optical depth from pyranometer measurements of surface solar radiation (global radiation) at Thessaloniki, Greece." Atmospheric Chemistry and Physics Discussions 12, no. 12 (2012): 33265–89. http://dx.doi.org/10.5194/acpd-12-33265-2012.
Testo completoAbstract (sommario):
Abstract. Pyranometer measurements of the solar surface radiation (SSR) are available at many locations worldwide, often as long time series covering several decades into the past. These data constitute a potential source of information on the atmospheric aerosol load. Here, we present a method for estimating the aerosol optical depth (AOD) using pyranometer measurements of the SSR together with total water vapor column information. The method, which is based on radiative transfer simulations, was developed and tested using recent data from Thessaloniki, Greece. The effective AOD calculated using this method was found to agree well with co-located AERONET measurements, exhibiting a correlation coefficient of 0.9 with 2/3 of the data found within ±20% or ±0.05 of the AERONET AOD. This is similar to the performance of current satellite aerosol methods. Differences in the AOD as compared to AERONET can be explained by variations in the aerosol properties of the atmosphere that are not accounted for in the idealized settings used in the radiative transfer simulations, such as variations in the single scattering albedo and Ångström exponent. Furthermore, the method is sensitive to calibration offsets between the radiative transfer simulations and the pyranometer SSR. The method provides an opportunity of extending our knowledge of the atmospheric aerosol load to locations and times not covered by dedicated aerosol measurements.
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Lindfors, A. V., N. Kouremeti, A. Arola, S. Kazadzis, A. F. Bais, and A. Laaksonen. "Effective aerosol optical depth from pyranometer measurements of surface solar radiation (global radiation) at Thessaloniki, Greece." Atmospheric Chemistry and Physics 13, no. 7 (2013): 3733–41. http://dx.doi.org/10.5194/acp-13-3733-2013.
Testo completoAbstract (sommario):
Abstract. Pyranometer measurements of the solar surface radiation (SSR) are available at many locations worldwide, often as long time series covering several decades into the past. These data constitute a potential source of information on the atmospheric aerosol load. Here, we present a method for estimating the aerosol optical depth (AOD) using pyranometer measurements of the SSR together with total water vapor column information. The method, which is based on radiative transfer simulations, was developed and tested using recent data from Thessaloniki, Greece. The effective AOD calculated using this method was found to agree well with co-located AERONET measurements, exhibiting a correlation coefficient of 0.9 with 2/3 of the data found within ±20% or ±0.05 of the AERONET AOD. This is similar to the performance of current satellite aerosol methods. Differences in the AOD as compared to AERONET can be explained by variations in the aerosol properties of the atmosphere that are not accounted for in the idealized settings used in the radiative transfer simulations, such as variations in the single scattering albedo and Ångström exponent. Furthermore, the method is sensitive to calibration offsets between the radiative transfer simulations and the pyranometer SSR. The method provides an opportunity of extending our knowledge of the atmospheric aerosol load to locations and times not covered by dedicated aerosol measurements.
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Kitzmann, D., A. B. C. Patzer, and H. Rauer. "On the Climatic Impact of CO2Ice Particles in Atmospheres of Terrestrial Exoplanets." Proceedings of the International Astronomical Union 8, S293 (2012): 303–8. http://dx.doi.org/10.1017/s1743921313013045.
Testo completoAbstract (sommario):
AbstractClouds play a significant role for the energy budget in planetary atmospheres. They can scatter incident stellar radiation back to space, effectively cooling the surface of terrestrial planets. On the other hand, they may contribute to the atmospheric greenhouse effect by trapping outgoing thermal radiation. For exoplanets near the outer boundary of the habitable zone, condensation of CO2can occur due to the low atmospheric temperatures. These CO2ice clouds may play an important role for the surface temperature and, therefore, for the question of habitability of those planets. However, the optical properties of CO2ice crystals differ significantly from those of water droplets or water ice particles. Except for a small number of strong absorption bands, they are almost transparent with respect to absorption. Instead, they are highly effective scatterers at long and short wavelengths. Therefore, the climatic effect of a CO2ice cloud will depend on how much incident stellar radiation is scattered to space in comparison to the amount of thermal radiation scattered back towards the planetary surface. This contribution aims at the potential greenhouse effect of CO2ice particles. Their scattering and absorption properties are calculated for assumed particle size distributions with different effective radii and particle densities. An accurate radiative transfer model is used to determine the atmospheric radiation field affected by such CO2particles. These results are compared to less detailed radiative transfer schemes employed in previous studies.
29
Stier, P., J. H. Seinfeld, S. Kinne, and O. Boucher. "Aerosol absorption and radiative forcing." Atmospheric Chemistry and Physics Discussions 7, no. 3 (2007): 7171–233. http://dx.doi.org/10.5194/acpd-7-7171-2007.
Testo completoAbstract (sommario):
Abstract. We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the short-wave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from –0.79 to –0.53 W m−2 (33%) and all-sky from –0.47 to –0.13 W m−2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19 W m−2 (36%) clear-sky and of 0.12 W m−2 (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05 W m−2 and a positive TOA forcing perturbation of 0.02 W m−2. The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.
30
Stier, P., J. H. Seinfeld, S. Kinne, and O. Boucher. "Aerosol absorption and radiative forcing." Atmospheric Chemistry and Physics 7, no. 19 (2007): 5237–61. http://dx.doi.org/10.5194/acp-7-5237-2007.
Testo completoAbstract (sommario):
Abstract. We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the short-wave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from −0.79 to −0.53 W m−2 (33%) and all-sky from −0.47 to −0.13 W m−2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19 W m−2 (36%) clear-sky and of 0.12 W m−2 (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05 W m−2 and a positive TOA forcing perturbation of 0.02 W m−2. The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.
31
Stubenrauch, C. J., F. Eddounia, J. M. Edwards, and A. Macke. "Evaluation of Cirrus Parameterizations for Radiative Flux Computations in Climate Models Using TOVS–ScaRaB Satellite Observations." Journal of Climate 20, no. 17 (2007): 4459–75. http://dx.doi.org/10.1175/jcli4251.1.
Testo completoAbstract (sommario):
Abstract Combined simultaneous satellite observations are used to evaluate the performance of parameterizations of the microphysical and optical properties of cirrus clouds used for radiative flux computations in climate models. Atmospheric and cirrus properties retrieved from Television and Infrared Observation Satellite (TIROS-N) Operational Vertical Sounder (TOVS) observations are given as input to the radiative transfer model developed for the Met Office climate model to simulate radiative fluxes at the top of the atmosphere (TOA). Simulated cirrus shortwave (SW) albedos are then compared to those retrieved from collocated Scanner for Radiation Budget (ScaRaB) observations. For the retrieval, special care has been given to angular direction models. Three parameterizations of cirrus ice crystal optical properties are represented in the Met Office radiative transfer model. These parameterizations are based on different physical approximations and different hypotheses on crystal habit. One parameterization assumes pristine ice crystals and two ice crystal aggregates. By relating the cirrus ice water path (IWP) retrieved from the effective infrared emissivity to the cirrus SW albedo, differences between the parameterizations are amplified. This study shows that pristine crystals seem to be plausible only for cirrus with IWP less than 30 g m−2. For larger IWP, ice crystal aggregates lead to cirrus SW albedos in better agreement with the observations. The data also indicate that climate models should allow the cirrus effective ice crystal diameter (De) to increase with IWP, especially in the range up to 30 g m−2. For cirrus with IWP less than 20 g m−2, this would lead to SW albedos that are about 0.02 higher than the ones of a constant De of 55 μm.
32
McCoy, Daniel T., Dennis L. Hartmann, and Daniel P. Grosvenor. "Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part I: Calculation of SW Flux from Observed Cloud Properties*." Journal of Climate 27, no. 23 (2014): 8836–57. http://dx.doi.org/10.1175/jcli-d-14-00287.1.
Testo completoAbstract (sommario):
Abstract The sensitivity of the reflection of shortwave radiation over the Southern Ocean to the cloud properties there is estimated using observations from a suite of passive and active satellite instruments in combination with radiative transfer modeling. A composite cloud property observational data description is constructed that consistently incorporates mean cloud liquid water content, ice water content, liquid and ice particle radius information, vertical structure, vertical overlap, and spatial aggregation of cloud water as measured by optical depth versus cloud-top pressure histograms. The observational datasets used are Moderate Resolution Imaging Spectroradiometer (MODIS) effective radius filtered to mitigate solar zenith angle bias, the Multiangle Imaging Spectroradiometer (MISR) cloud-top height–optical depth (CTH–OD) histogram, the liquid water path from the University of Wisconsin dataset, and ice cloud properties from CloudSat. This cloud database is used to compute reflected shortwave radiation as a function of month and location over the ocean from 40° to 60°S, which compares well with observations of reflected shortwave radiation. This calculation is then used to test the sensitivity of the seasonal variation of shortwave reflection to the observed seasonal variation of cloud properties. Effective radius decreases during the summer season, which results in an increase in reflected solar radiation of 4–8 W m−2 during summer compared to what would be reflected if the effective radius remained constant at its annual-mean value. Summertime increases in low cloud fraction similarly increase the summertime reflection of solar radiation by 9–11 W m−2. In-cloud liquid water path is less in summertime, causing the reflected solar radiation to be 1–4 W m−2 less.
33
Ren, Yatao, Hong Qi, Qin Chen, and Liming Ruan. "Inverse Transient Radiative Analysis in Two-Dimensional Turbid Media by Particle Swarm Optimizations." Mathematical Problems in Engineering 2015 (2015): 1–15. http://dx.doi.org/10.1155/2015/680823.
Testo completoAbstract (sommario):
Three intelligent optimization algorithms, namely, the standard Particle Swarm Optimization (PSO), the Stochastic Particle Swarm Optimization (SPSO), and the hybrid Differential Evolution-Particle Swarm Optimization (DE-PSO), were applied to solve the inverse transient radiation problem in two-dimensional (2D) turbid media irradiated by the short pulse laser. The time-resolved radiative intensity signals simulated by finite volume method (FVM) were served as input for the inverse analysis. The sensitivities of the time-resolved radiation signals to the geometric parameters of the circular inclusions were also investigated. To illustrate the performance of these PSO algorithms, the optical properties, the size, and location of the circular inclusion were retrieved, respectively. The results showed that all these radiative parameters could be estimated accurately, even with noisy data. Compared with the PSO algorithm with inertia weights, the SPSO and DE-PSO algorithm were demonstrated to be more effective and robust, which had the potential to be implemented in 2D transient radiative transfer inverse problems.
34
Orlov, N. Yu, S. Yu Gus'kov, S. A. Pikuz, et al. "Theoretical and experimental studies of the radiative properties of hot dense matter for optimizing soft X-ray sources." Laser and Particle Beams 25, no. 3 (2007): 415–23. http://dx.doi.org/10.1017/s0263034607000535.
Testo completoAbstract (sommario):
Theoretical and experimental studies of radiative properties of hot dense plasmas that are used as soft X-ray sources have been carried out depending on the plasma composition. Important features of the theoretical model, which can be used for complex materials, are discussed. An optimizing procedure that can determine an effective complex material to produce optically thick plasma by laser interaction with a thick solid target is applied. The efficiency of the resulting material is compared with the efficiency of other composite materials that have previously been evaluated theoretically. It is shown that the optimizing procedure does, in practice, find higher radiation efficiency materials than have been found by previous authors. Similar theoretical research is performed for the optically thin plasma produced from exploding wires. Theoretical estimations of radiative efficiency are compared with experimental data that are obtained from measurements of X-pinch radiation energy yield using two exploding wire materials, NiCr and Alloy 188. It is shown that theoretical calculations agree well with the experimental data.
35
Shi, Xiangjun, Chunhan Li, Lijuan Li, Wentao Zhang, and Jiaojiao Liu. "Estimating the CMIP6 Anthropogenic Aerosol Radiative Effects with the Advantage of Prescribed Aerosol Forcing." Atmosphere 12, no. 3 (2021): 406. http://dx.doi.org/10.3390/atmos12030406.
Testo completoAbstract (sommario):
The prescribed anthropogenic aerosol forcing recommended by Coupled Model Intercomparison Project Phase 6 (CMIP6) was implemented in an atmospheric model. With the reduced complexity of anthropogenic aerosol forcing, each component of anthropogenic aerosol effective radiative forcing (ERF) can be estimated by one or more calculation methods, especially for instantaneous radiative forcing (RF) from aerosol–radiation interactions (RFari) and aerosol–cloud interactions (RFaci). Simulation results show that the choice of calculation method might impact the magnitude and reliability of RFari. The RFaci—calculated by double radiation calls—is the definition-based Twomey effect, which previously was impossible to diagnose using the default model with physically based aerosol–cloud interactions. The RFari and RFaci determined from present-day simulations are very robust and can be used as offline simulation results. The robust RFari, RFaci, and corresponding radiative forcing efficiencies (i.e., the impact of environmental properties) are very useful for analyzing anthropogenic aerosol radiative effects. For instance, from 1975 to 2000, both RFari and RFaci showed a clear response to the spatial change of anthropogenic aerosol. The global average RF (RFari + RFaci) has enhanced (more negative) by ~6%, even with a slight decrease in the global average anthropogenic aerosol, and this can be explained by the spatial pattern of radiative forcing efficiency.
36
Bae, Soo Ya, Song-You Hong, and Kyo-Sun Sunny Lim. "Coupling WRF Double-Moment 6-Class Microphysics Schemes to RRTMG Radiation Scheme in Weather Research Forecasting Model." Advances in Meteorology 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/5070154.
Testo completoAbstract (sommario):
A method to explicitly calculate the effective radius of hydrometeors in the Weather Research Forecasting (WRF) double-moment 6-class (WDM6) microphysics scheme is designed to tackle the physical inconsistency in cloud properties between the microphysics and radiation processes. At each model time step, the calculated effective radii of hydrometeors from the WDM6 scheme are linked to the Rapid Radiative Transfer Model for GCMs (RRTMG) scheme to consider the cloud effects in radiative flux calculation. This coupling effect of cloud properties between the WDM6 and RRTMG algorithms is examined for a heavy rainfall event in Korea during 25–27 July 2011, and it is compared to the results from the control simulation in which the effective radius is prescribed as a constant value. It is found that the derived radii of hydrometeors in the WDM6 scheme are generally larger than the prescribed values in the RRTMG scheme. Consequently, shortwave fluxes reaching the ground (SWDOWN) are increased over less cloudy regions, showing a better agreement with a satellite image. The overall distribution of the 24-hour accumulated rainfall is not affected but its amount is changed. A spurious rainfall peak over the Yellow Sea is alleviated, whereas the local maximum in the central part of the peninsula is increased.
37
De León, R. R., M. Krämer, D. S. Lee, and J. C. Thelen. "Sensitivity of radiative properties of persistent contrails to the ice water path." Atmospheric Chemistry and Physics 12, no. 17 (2012): 7893–901. http://dx.doi.org/10.5194/acp-12-7893-2012.
Testo completoAbstract (sommario):
Abstract. The dependence of the radiative properties of persistent linear contrails on the variability of their ice water path is assessed in a two-stream radiative transfer model. It is assumed that the ice water content and the effective size of ice crystals in aged contrails do not differ from those observed in natural cirrus; the parameterization of these two variables, based on a correlation with ambient temperature derived from in situ observations, allows a more realistic representation than the common assumption of fixed values for the contrail optical depth and ice crystal effective radius. The results show that the large variability in ice water content that aged contrails may share with natural cirrus, together with an assumed contrail vertical thickness between 220 and 1000 m, translate into a wider range of radiative forcings from linear contrails [1 to 66 m Wm−2] than that reported in previous studies, including IPCC's [3 to 30 m Wm−2]. Further field and modelling studies of the temporal evolution of contrail properties will thus be needed to reduce the uncertainties associated with the values assumed in large scale contrail studies.
38
Pincus, Robert, Piers M. Forster, and Bjorn Stevens. "The Radiative Forcing Model Intercomparison Project (RFMIP): experimental protocol for CMIP6." Geoscientific Model Development 9, no. 9 (2016): 3447–60. http://dx.doi.org/10.5194/gmd-9-3447-2016.
Testo completoAbstract (sommario):
Abstract. The phrasing of the first of three questions motivating CMIP6 – “How does the Earth system respond to forcing?” – suggests that forcing is always well-known, yet the radiative forcing to which this question refers has historically been uncertain in coordinated experiments even as understanding of how best to infer radiative forcing has evolved. The Radiative Forcing Model Intercomparison Project (RFMIP) endorsed by CMIP6 seeks to provide a foundation for answering the question through three related activities: (i) accurate characterization of the effective radiative forcing relative to a near-preindustrial baseline and careful diagnosis of the components of this forcing; (ii) assessment of the absolute accuracy of clear-sky radiative transfer parameterizations against reference models on the global scales relevant for climate modeling; and (iii) identification of robust model responses to tightly specified aerosol radiative forcing from 1850 to present. Complete characterization of effective radiative forcing can be accomplished with 180 years (Tier 1) of atmosphere-only simulation using a sea-surface temperature and sea ice concentration climatology derived from the host model's preindustrial control simulation. Assessment of parameterization error requires trivial amounts of computation but the development of small amounts of infrastructure: new, spectrally detailed diagnostic output requested as two snapshots at present-day and preindustrial conditions, and results from the model's radiation code applied to specified atmospheric conditions. The search for robust responses to aerosol changes relies on the CMIP6 specification of anthropogenic aerosol properties; models using this specification can contribute to RFMIP with no additional simulation, while those using a full aerosol model are requested to perform at least one and up to four 165-year coupled ocean–atmosphere simulations at Tier 1.
39
Orlov, N. Yu, O. B. Denisov, O. N. Rosmej, et al. "Theoretical and experimental studies of material radiative properties and their applications to laser and heavy ion inertial fusion." Laser and Particle Beams 29, no. 1 (2011): 69–80. http://dx.doi.org/10.1017/s0263034610000777.
Testo completoAbstract (sommario):
AbstractTheoretical and experimental studies of radiative properties of substances heated by pulsed current devises or lasers and used as X-ray sources have been carried out depending on plasma conditions, and specific spectra of X-ray absorption and radiation for different materials have been calculated. Important features of the theoretical model, known as the ion model of plasma, are discussed. This model can be applied for calculations of the radiative properties of complex materials over a wide range of plasma parameters. For purposes of indirect-driven inertial fusion based on the hohlraum concept, an optimization method is used for the selection of an effective complex hohlraum wall material, which provides high radiation efficiency at laser interaction with the wall. The radiation efficiency of the resulting material is compared with the efficiency of other composite materials that have previously been evaluated theoretically. A similar theoretical study is performed for the optically thin X-pinch plasma produced by exploding wires. Theoretical estimations of radiative efficiency are compared with experimental data that have been obtained from measurements of X-pinch radiation energy yield using two exploding wire materials, NiCr and Alloy 188. It is shown that the theoretical results agree well with the experimental data. A symmetric multilayer X-pinch, where W and Mo wires are used, is as well considered. The theoretical explanation of experimental phenomena is discussed based on the W and Mo radiative spectra. The ion model was as well applied for interpretation of experimental results on opacities of CHO-plasma obtained via indirect heating of low density polymer layers by means of soft X-rays. The new diagnostics method based on the deformation of the of the Carbon absorption K-edge when foam layer is heated to plasma is discussed. The spectral coefficients for X-ray absorption in CHO-plasma are calculated in the photon energy region around the Carbon K-edge for different plasma temperatures and mean foam density. In this case, the Carbon K-edge position on the energy scale can be used for plasma temperature diagnostic.
40
Hoang, Thiem. "Rotational Disruption of Astrophysical Dust and Ice—Theory and Applications." Galaxies 8, no. 3 (2020): 52. http://dx.doi.org/10.3390/galaxies8030052.
Testo completoAbstract (sommario):
Dust is an essential component of the interstellar medium (ISM) and plays an important role in many different astrophysical processes and phenomena. Traditionally, dust grains are known to be destroyed by thermal sublimation, Coulomb explosions, sputtering, and shattering. The first two mechanisms arise from the interaction of dust with intense radiation fields and high-energy photons (extreme UV), which work in a limited astrophysical environment. The present review is focused on a new destruction mechanism present in the dust-radiation interaction that is effective in a wide range of radiation fields and has ubiquitous applications in astrophysics. We first describe this new mechanism of grain destruction, namely rotational disruption induced by Radiative Torques (RATs) or RAdiative Torque Disruption (RATD). We then discuss rotational disruption of nanoparticles by mechanical torques due to supersonic motion of grains relative to the ambient gas, which is termed MEchanical Torque Disruption (METD). These two new mechanisms modify properties of dust and ice (e.g., size distribution and mass), which affects observational properties, including dust extinction, thermal and nonthermal emission, and polarization. We present various applications of the RATD and METD mechanisms for different environments, including the ISM, star-forming regions, astrophysical transients, and surface astrochemistry.
41
Hong, Yulan, and Guosheng Liu. "The Characteristics of Ice Cloud Properties Derived from CloudSat and CALIPSO Measurements." Journal of Climate 28, no. 9 (2015): 3880–901. http://dx.doi.org/10.1175/jcli-d-14-00666.1.
Testo completoAbstract (sommario):
Abstract The characteristics of ice clouds with a wide range of optical depths are studied based on satellite retrievals and radiative transfer modeling. Results show that the global-mean ice cloud optical depth, ice water path, and effective radius are approximately 2, 109 g m−2, and 48 , respectively. Ice cloud occurrence frequency varies depending not only on regions and seasons, but also on the types of ice clouds as defined by optical depth values. Ice clouds with different values show differently preferential locations on the planet; optically thinner ones ( &lt; 3) are most frequently observed in the tropics around 15 km and in midlatitudes below 5 km, while thicker ones ( &gt; 3) occur frequently in tropical convective areas and along midlatitude storm tracks. It is also found that ice water content and effective radius show different temperature dependence among the tropics, midlatitudes, and high latitudes. Based on analyzed ice cloud frequencies and microphysical properties, cloud radiative forcing is evaluated using a radiative transfer model. The results show that globally radiative forcing due to ice clouds introduces a net warming of the earth–atmosphere system. Those with &lt; 4.0 all have a positive (warming) net forcing with the largest contribution by ice clouds with ~ 1.2. Regionally, ice clouds in high latitudes show a warming effect throughout the year, while they cause cooling during warm seasons but warming during cold seasons in midlatitudes. Ice cloud properties revealed in this study enhance the understanding of ice cloud climatology and can be used for validating climate models.
42
Hong, Gang, Ping Yang, Bryan A. Baum, Andrew J. Heymsfield, and Kuan-Man Xu. "Parameterization of Shortwave and Longwave Radiative Properties of Ice Clouds for Use in Climate Models." Journal of Climate 22, no. 23 (2009): 6287–312. http://dx.doi.org/10.1175/2009jcli2844.1.
Testo completoAbstract (sommario):
Abstract Climate modeling and prediction require that the parameterization of the radiative effects of ice clouds be as accurate as possible. The radiative properties of ice clouds are highly sensitive to the single-scattering properties of ice particles and ice cloud microphysical properties such as particle habits and size distributions. In this study, parameterizations for shortwave (SW) and longwave (LW) radiative properties of ice clouds are developed for three existing schemes using ice cloud microphysical properties obtained from five field campaigns and broadband-averaged single-scattering properties of nonspherical ice particles as functions of the effective particle size De (defined as 1.5 times the ratio of total volume to total projected area), which include hexagonal solid columns and hollow columns, hexagonal plates, six-branch bullet rosettes, aggregates, and droxtals. A combination of the discrete ordinates radiative transfer model and a line-by-line model is used to simulate ice cloud radiative forcing (CRF) at both the surface and the top of the atmosphere (TOA) for the three redeveloped parameterization schemes. The differences in CRF for different parameterization schemes are in the range of −5 to 5 W m−2. In general, the large differences in SW and total CRF occur for thick ice clouds, whereas the large differences in LW CRF occur for ice clouds with small ice particles (De less than 20 μm). The redeveloped parameterization schemes are then applied to the radiative transfer models used for climate models. The ice cloud optical and microphysical properties from the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product over a granule and the collocated atmospheric profiles from the Atmospheric Infrared Sounder (AIRS) product are input into these radiative transfer models to compare the differences in CRF between the redeveloped and existing parameterization schemes. Although differences between these schemes are small in the LW CRF, the differences in the SW CRF are quite large.
43
Peyrusse, O., C. Bauche-Arnoult, and J. Bauche. "Effective superconfiguration temperature and the radiative properties of nonlocal thermodynamical equilibrium hot dense plasma." Physics of Plasmas 12, no. 6 (2005): 063302. http://dx.doi.org/10.1063/1.1931109.
Testo completo
44
Spang, Reinhold, Rolf Müller, and Alexandru Rap. "Radiative effect of thin cirrus clouds in the extratropical lowermost stratosphere and tropopause region." Atmospheric Chemistry and Physics 24, no. 2 (2024): 1213–30. http://dx.doi.org/10.5194/acp-24-1213-2024.
Testo completoAbstract (sommario):
Abstract. Cirrus clouds play an important role in the radiation budget of the Earth; nonetheless, the radiative effect of ultra-thin cirrus clouds in the tropopause region and in the lowermost stratosphere remains poorly constrained. These clouds have a small vertical extent and optical depth and are frequently neither observed even by sensitive sensors nor considered in climate model simulations. In addition, their short-wave (cooling) and long-wave (warming) radiative effects are often in approximate balance, and their net effect strongly depends on the shape and size of the cirrus particles. However, the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere instrument (CRISTA-2) allows ultra-thin cirrus clouds to be detected. Here we use CRISTA-2 observations in summer 1997 in the Northern Hemisphere midlatitudes together with the Suite Of Community RAdiative Transfer codes based on Edwards and Slingo (SOCRATES) radiative transfer model to calculate the radiative effect of observed ultra-thin cirrus. Using sensitivity simulations with different ice effective particle size and shape, we provide an estimate of the uncertainty in the radiative effect of ultra-thin cirrus in the extratropical lowermost stratosphere and tropopause region during summer and – by extrapolation of the summer results – for winter. Cloud top height and ice water content are based on CRISTA-2 measurements, while the cloud vertical thickness was predefined to be 0.5 or 2 km. Our results indicate that if the ice crystals of these thin cirrus clouds are assumed to be spherical, their net cloud radiative effect is generally positive (warming). In contrast, assuming aggregates or a hexagonal shape, their net radiative effect is generally negative (cooling) during summer months and very likely positive (warming) during winter. The radiative effect is in the order of ±(0.1–0.01) W m−2 for a realistic global cloud coverage of 10 %, similar to the magnitude of the contrail cirrus radiative forcing (of ∼ 0.1 W m−2). The radiative effect is also dependent on the cloud vertical extent and consequently the optically thickness and effective radius of the particle size distribution (e.g. effective radius increase from 5 to 30 µm results in a factor ∼ 6 smaller long- and short-wave effects, respectively). The properties of ultra-thin cirrus clouds in the lowermost stratosphere and tropopause region need to be better observed, and ultra-thin cirrus clouds need to be evaluated in climate model simulations.
45
Chiu, J. C., A. Marshak, Y. Knyazikhin, and W. J. Wiscombe. "Spectral invariant behavior of zenith radiance around cloud edges simulated by radiative transfer." Atmospheric Chemistry and Physics Discussions 10, no. 6 (2010): 14557–81. http://dx.doi.org/10.5194/acpd-10-14557-2010.
Testo completoAbstract (sommario):
Abstract. A previous paper discovered a surprising spectral-invariant relationship in shortwave spectrometer observations taken by the Atmospheric Radiation Measurement (ARM) program. Here, using radiative transfer simulations, we study the sensitivity of this relationship to the properties of aerosols and clouds, to the underlying surface type, and to the finite field-of-view (FOV) of the spectrometer. Overall, the relationship is mostly sensitive to cloud properties and has little sensitivity to the other factors. At visible wavelengths, the relationship primarily depends on cloud optical depth regardless of cloud thermodynamic phase and drop size. At water-absorbing wavelengths, the slope of the spectral-invariant relationship depends primarily on cloud optical depth; the intercept, by contrast, depends primarily on cloud absorption properties, suggesting a new retrieval method for cloud drop effective radius. These results suggest that the spectral-invariant relationship can be used to infer cloud properties even with insufficient or no knowledge about spectral surface albedo and aerosol properties.
46
Okamura, Rintaro, Hironobu Iwabuchi, and K. Sebastian Schmidt. "Feasibility study of multi-pixel retrieval of optical thickness and droplet effective radius of inhomogeneous clouds using deep learning." Atmospheric Measurement Techniques 10, no. 12 (2017): 4747–59. http://dx.doi.org/10.5194/amt-10-4747-2017.
Testo completoAbstract (sommario):
Abstract. Three-dimensional (3-D) radiative-transfer effects are a major source of retrieval errors in satellite-based optical remote sensing of clouds. The challenge is that 3-D effects manifest themselves across multiple satellite pixels, which traditional single-pixel approaches cannot capture. In this study, we present two multi-pixel retrieval approaches based on deep learning, a technique that is becoming increasingly successful for complex problems in engineering and other areas. Specifically, we use deep neural networks (DNNs) to obtain multi-pixel estimates of cloud optical thickness and column-mean cloud droplet effective radius from multispectral, multi-pixel radiances. The first DNN method corrects traditional bispectral retrievals based on the plane-parallel homogeneous cloud assumption using the reflectances at the same two wavelengths. The other DNN method uses so-called convolutional layers and retrieves cloud properties directly from the reflectances at four wavelengths. The DNN methods are trained and tested on cloud fields from large-eddy simulations used as input to a 3-D radiative-transfer model to simulate upward radiances. The second DNN-based retrieval, sidestepping the bispectral retrieval step through convolutional layers, is shown to be more accurate. It reduces 3-D radiative-transfer effects that would otherwise affect the radiance values and estimates cloud properties robustly even for optically thick clouds.
47
Wan, Linfeng, Xi Zhang, and Tanguy Bertrand. "Effects of Haze Radiation and Eddy Heat Transport on the Thermal Structure of Pluto’s Lower Atmosphere." Astrophysical Journal 922, no. 2 (2021): 244. http://dx.doi.org/10.3847/1538-4357/ac25f2.
Testo completoAbstract (sommario):
Abstract The temperature profile of Pluto’s atmosphere has generally been assumed in a radiative–conductive equilibrium. Recent studies further highlighted the importance of radiative heating and cooling effects by haze particles. In this study, we update results from Zhang et al. by taking into account the icy haze composition proposed by Lavvas et al., and find that radiation of such an icy haze could still dominate the energy balance in the middle and upper atmosphere and explain the cold temperature observed by New Horizons. However, additional considerations are needed to explain the rapid decrease in temperature toward the icy surface at altitudes <25 km. We propose that vertical eddy heat transport might help maintain radiative–diffusive equilibrium in the lower atmosphere. In this scenario, our radiative–conductive–diffusive model (including both gas and haze) would match observations if the eddy diffusivity is on the order of 103 cm2 s−1. Alternatively, if eddy heat transport is not effective on Pluto, in order to match observations, haze albedo must increase rapidly with decreasing altitude and approach unity near the surface. This is a plausible result of additional ice condensation and/or cloud formation. In this scenario, haze radiation might still dominate over gas radiation and heat conduction to maintain radiative equilibrium. Better constraints on haze albedo at ultraviolet and visible wavelengths would be a key to distinguish these two scenarios. Future mid-infrared observations from the James Webb Space Telescope could also constrain the thermal emission and haze properties in Pluto’s lower atmosphere.
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Costa, Tiago, Joakim Rosdahl, and Taysun Kimm. "The hidden satellites of massive galaxies and quasars at high redshift." Monthly Notices of the Royal Astronomical Society 489, no. 4 (2019): 5181–86. http://dx.doi.org/10.1093/mnras/stz2471.
Testo completoAbstract (sommario):
ABSTRACT Using cosmological, radiation-hydrodynamic simulations targeting a rare ${\approx}2 \times 10^{12} \, \rm {\rm M}_{\odot }$ halo at $z = 6$, we show that the number counts and internal properties of satellite galaxies within the massive halo are sensitively regulated by a combination of local stellar radiative feedback and strong tidal forces. Radiative feedback operates before the first supernova explosions erupt and results in less tightly bound galaxies. Satellites are therefore more vulnerable to tidal stripping when they accrete on to the main progenitor and are tidally disrupted on a significantly shorter time-scale. Consequently, the number of satellites with $M_{\rm \star } \gt 10^{7} \, \rm {\rm M}_{\odot }$ within the parent system’s virial radius drops by up to $60 \, {\rm per\, cent}$ with respect to an identical simulation performed without stellar radiative feedback. Radiative feedback also impacts the central galaxy, whose effective radius increases by a factor ≲3 due to the presence of a more extended and diffuse stellar component. We suggest that the number of satellites in the vicinity of massive high-redshift galaxies is an indication of the strength of stellar radiative feedback and can be anomalously low in the extreme cosmic environments of high-redshift quasars.
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Zhao, C. Y., T. J. Lu, and H. P. Hodson. "Measurements of thermal radiation in ultralight metal foams with open cells." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, no. 11 (2004): 1297–307. http://dx.doi.org/10.1177/095440620421801102.
Testo completoAbstract (sommario):
Highly porous ultralightweight cellular metal foams with open cells have attractive mechanical, thermal, acoustic and other properties and are currently being exploited for hightemperature applications (e.g. acoustic liners for combustion chambers). In such circumstances, thermal radiation in the metal foam becomes a significant mechanism of heat transfer. This paper presents results from experimental measurements on radiative transfer in Fe-Cr-Al-Y (a steel-based high-temperature alloy) foams having high porosity (95 per cent) and different cell sizes, manufactured at low cost from the sintering route. The spectral transmittance and reflectance are measured at different infrared wavelengths ranging from 2.5 to 50 μ, which are subsequently used to determine the extinction coefficient and foam emissivity. The results show that the spectral quantities are strongly dependent on the wavelength, particularly in the short-wavelength regime (less than 25 μ). While the extinction coefficient decreases with increasing cell size, the effect of cell size on foam reflectance is not significant. When the temperature is increased, the total extinction coefficient increases but the total reflectance decreases. The effective radiative conductivity of the metal foam is obtained by using the guarded hot-plate apparatus. With the porosity fixed, the effective radiative conductivity increases with increasing cell size and increasing temperature.
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Lampert, A., A. Ehrlich, A. Dörnbrack, et al. "Microphysical and radiative characterization of a subvisible midlevel Arctic ice cloud by airborne observations – a case study." Atmospheric Chemistry and Physics 9, no. 8 (2009): 2647–61. http://dx.doi.org/10.5194/acp-9-2647-2009.
Testo completoAbstract (sommario):
Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign, which was conducted in March and April 2007, an optically thin ice cloud was observed south of Svalbard at around 3 km altitude. The microphysical and radiative properties of this particular subvisible midlevel cloud were investigated with complementary remote sensing and in situ instruments. Collocated airborne lidar remote sensing and spectral solar radiation measurements were performed at a flight altitude of 2300 m below the cloud base. Under almost stationary atmospheric conditions, the same subvisible midlevel cloud was probed with various in situ sensors roughly 30 min later. From individual ice crystal samples detected with the Cloud Particle Imager and the ensemble of particles measured with the Polar Nephelometer, microphysical properties were retrieved with a bi-modal inversion algorithm. The best agreement with the measurements was obtained for small ice spheres and deeply rough hexagonal ice crystals. Furthermore, the single-scattering albedo, the scattering phase function as well as the volume extinction coefficient and the effective diameter of the crystal population were determined. A lidar ratio of 21(±6) sr was deduced by three independent methods. These parameters in conjunction with the cloud optical thickness obtained from the lidar measurements were used to compute spectral and broadband radiances and irradiances with a radiative transfer code. The simulated results agreed with the observed spectral downwelling radiance within the range given by the measurement uncertainty. Furthermore, the broadband radiative simulations estimated a net (solar plus thermal infrared) radiative forcing of the subvisible midlevel ice cloud of −0.4 W m−2 (−3.2 W m−2 in the solar and +2.8 W m−2 in the thermal infrared wavelength range).