Radiative transfer

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

Radiative forcing of climate by hydrochlorofluorocarbons and hydrofluorocarbons

Abstract: We measure infrared absorption spectra of 18 hydrochlorofluorocarbons and hydrofluorocarbons, seven of which do not yet appear in the literature. The spectra are used in a narrowband model of the terrestrial infrared radiation to calculate radiative forcing and global warming potentials. We investigate the sensitivity of the radiative forcing to the absorption spectrum temperature dependence, halocarbon vertical profile, stratospheric adjustment, cloudiness, spectral overlap, and latitude, and we make some recommendations for the reporting of radiative forcings that would help to resolve discrepancies between assessments. We investigate simple methods of estimating instantaneous radiative forcing directly from a molecule's absorption spectrum and we present a new method that agrees to within 0.3% with our narrowband model results.

Double optical resonance

Abstract: A complete and detailed treatment of a three-level atom interacting with two near-resonant monochromatic fields is presented. It is assumed that the only damping mechanism is radiative damping, and that the atoms all have the same resonance frequencies, as is the case in an atomic beam. Detailed analytic solutions as well as numerical examples are determined from quantum-electrodynamic equations of motion. In addition, approximation techniques are presented which allow one to get accurate quantitative predictions for strong applied fields from simple rate-equation-like arguments. Absorption and emission spectra are determined, as are the transient and steady-state response of the atom. Two of the more interesting predictions are an emission spectrum containing up to seven components and a prediction of steady-state populations larger than 0.5 in the second excited state.

Effect of precipitation on the albedo susceptibility of clouds in the marine boundary layer

Abstract: TROPOSPHERIC aerosols are thought to have three important effects on the Earth's radiation budget: the direct radiative effect1 (pertur-bation of clear-sky reflectivity), the indirect radiative effect2 (modi-fication of cloud albedo) and the effect on the hydrological cycle3 (modification of the vertical thickness and horizontal extent of clouds). The first two effects have been understood in principle for nearly 20 years, and quantitative estimates of their magnitudes have been provided by models and observations4. The third phe-nomenon, and its relation to the other two, has received far less attention. Previous work3 has shown, however, that increases in aerosol concentration may act to increase cloud albedo by increas-ing horizontal cloud fraction as well as cloud reflectivity. Here we use a simple model of the marine cloud-topped boundary layer to investigate the changes in cloud thickness and albedo that result from changes in precipitation as particle concentrations vary. We find that the sensitivity of layer cloud albedo to droplet number concentration (the albedo susceptibility) is increased by 50–200% when the dependence of cloud thickness on particle number is included. The results suggest that the response of cloud thickness to changes in aerosol particle concentration must be taken into account for accurate prediction of global albedo by climate models.