Radiative transfer

About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.

Infrared emissivities of silicates: Experimental results and a cloudy atmosphere model of Spectral emission from condensed particulate mediums

Abstract: Infrared emissivities of powered silicates are shown by experiment to contain new maximums and minimums that are representative of both composition and particle size. A cloudy atmosphere model for radiative transfer in a condensed powder is developed in which the scatter is considered to be both nonconservative and linearly anisotropic. The scattering parameters are computed as functions of frequency from the Mie diffraction theory. Detailed calculations of the spectral emissivity of quartz are presented. The model is shown to account for many features observed experimentally in the spectrums of quartz powders and sand. Changes in the spectrum with particle size can be understood in terms of changes in the albedo for single scattering and the degree of forward scatter with particle size. The principal Christiansen frequencies of silicate powder films obtained from transmission measurements are shown to be diagnostic of mineralogy and to be frequencies of maximum emissivity for powders. The relationship is discussed in detail for quartz.

The Mathematics of Radiative Transfer

Abstract: Part I Auxiliary Mathematics: 1 The Equation of Transfer 2 The H- Functions 3 Integral Operators Part II Milne Equations: 4 Iterative Solutions 5 The Wiener-Hopf Solution 6 Solutions of the Non-Homogeneous Equation 7 Finite Atmospheres: Preliminary Results 8 The X- and Y-Functions 9 Finite Atmospheres: Further Results 10 Anisothropic Scattering

Coupling aerosol-cloud-radiative processes in the WRF-Chem model: Investigating the radiative impact of elevated point sources

Abstract: . The local and regional influence of elevated point sources on summertime aerosol forcing and cloud-aerosol interactions in northeastern North America was investigated using the WRF-Chem community model. The direct effects of aerosols on incoming solar radiation were simulated using existing modules to relate aerosol sizes and chemical composition to aerosol optical properties. Indirect effects were simulated by adding a prognostic treatment of cloud droplet number and adding modules that activate aerosol particles to form cloud droplets, simulate aqueous-phase chemistry, and tie a two-moment treatment of cloud water (cloud water mass and cloud droplet number) to precipitation and an existing radiation scheme. Fully interactive feedbacks thus were created within the modified model, with aerosols affecting cloud droplet number and cloud radiative properties, and clouds altering aerosol size and composition via aqueous processes, wet scavenging, and gas-phase-related photolytic processes. Comparisons of a baseline simulation with observations show that the model captured the general temporal cycle of aerosol optical depths (AODs) and produced clouds of comparable thickness to observations at approximately the proper times and places. The model overpredicted SO2 mixing ratios and PM2.5 mass, but reproduced the range of observed SO2 to sulfate aerosol ratios, suggesting that atmospheric oxidation processes leading to aerosol sulfate formation are captured in the model. The baseline simulation was compared to a sensitivity simulation in which all emissions at model levels above the surface layer were set to zero, thus removing stack emissions. Instantaneous, site-specific differences for aerosol and cloud related properties between the two simulations could be quite large, as removing above-surface emission sources influenced when and where clouds formed within the modeling domain. When summed spatially over the finest resolution model domain (the extent of which corresponds to the typical size of a single global climate model grid cell) and temporally over a three day analysis period, total rainfall in the sensitivity simulation increased by 31% over that in the baseline simulation. Fewer optically thin clouds, arbitrarily defined as a cloud exhibiting an optical depth less than 1, formed in the sensitivity simulation. Domain-averaged AODs dropped from 0.46 in the baseline simulation to 0.38 in the sensitivity simulation. The overall net effect of additional aerosols attributable to primary particulates and aerosol precursors from point source emissions above the surface was a domain-averaged reduction of 5 W m−2 in mean daytime downwelling shortwave radiation.

Spectral Energy Distributions of Passive T Tauri and Herbig Ae Disks: Grain Mineralogy, Parameter Dependences, and Comparison with Infrared Space Observatory LWS Observations

Abstract: We improve upon the radiative, hydrostatic equilibrium models of passive circumstellar disks constructed by Chiang & Goldreich. New features include (1) an account for a range of particle sizes, (2) employment of laboratory-based optical constants of representative grain materials, and (3) numerical solution of the equations of radiative and hydrostatic equilibrium within the original two-layer (disk surface plus disk interior) approximation. We systematically explore how the spectral energy distribution (SED) of a face-on disk depends on grain size distributions, disk geometries and surface densities, and stellar photospheric temperatures. Observed SEDs of three Herbig Ae and two T Tauri stars, including spectra from the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO), are fitted with our models. Silicate emission bands from optically thin, superheated disk surface layers appear in nearly all systems. Water ice emission bands appear in LWS spectra of two of the coolest stars. Infrared excesses in several sources are consistent with significant vertical settling of photospheric grains. While this work furnishes further evidence that passive reprocessing of starlight by flared disks adequately explains the origin of infrared-to-millimeter wavelength excesses of young stars, we emphasize by explicit calculations how the SED alone does not provide sufficient information to constrain particle sizes and disk masses uniquely.