Showing papers on "Radiative transfer published in 1974"

Principles of Environmental Physics

Abstract: PREFACE TO THE SECOND EDITION LIST OF SYMBOLS 1. SCOPE OF ENVIRONMENTAL PHYSICS 2. GAS LAWS Pressure, volume and temperature Specific heats Lapse rate Water and water vapour Other gases 3. TRANSPORT LAWS General transfer equation Molecular transfer processes Diffusion coefficients Radiation laws 4. RADIATION ENVIRONMENT Solar radiation Terrestrial radiation Net radiation 5. MICROCLIMATOLOGY OF RADIATION (i) Interception Direct solar radiation Diffuse radiation Radiation in crop canopies 6. MICROCLIMATOLOGY OF RADIATION (ii) Absorption and reflection Radiative properties of natural materials Net radiation 7. MOMENTUM TRANSFER Boundary layers Wind profiles and drag on uniform surfaces Lodging and windthrow 8. HEAT TRANSFER Convection Non-dimensional groups Measurements of convection Conduction Insulation of animals 9. MASS TRANSFER (i) Gases and water vapour Non-dimensional groups Measurement of mass transfer Ventilation Mass transfer through pores Coats and clothing 10.MASS TRANSFER (ii) Particles Steady motion 11.STEADY STATE HEAT BALANCE (i) Water surfaces and vegetation Heat balance equation Heat balance of thermometers Heat balance of surfaces Developments from the Penman Equation 12.STEADY STATE HEAT BALANCE (ii) Animals Heat balance components The thermo-neutral diagram Specification of the environment Case studies 13.TRANSIENT HEAT BALANCE Time constant General cases Heat flow in soil 14.CROP MICROMETEOROLOGY (i) Profiles and fluxes Profiles Profile equations and stability Measurement of flux above the canopy 15.CROP MICROMETEOROLOGY (ii) Interpretation of measurements Resistance analogues Case studies: Water vapour and transpiration Carbon dioxide and growth Sulphur dioxide and pollutant fluxes to crops Transport within canopies APPENDIX BIBLIOGRAPHY REFERENCES INDEX

Light scattering in planetary atmospheres

Abstract: This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

The Effects of Mountains on the General Circulation of the Atmosphere as Identified by Numerical Experiments

Abstract: In order to identify the effects of mountains upon the general circulation of the atmosphere, a set of numerical experiments is performed by use of a general circulation model developed at the Geophysical Fluid Dynamics Laboratory of NOAA. The numerical time integrations of the model are performed with and without the effects of mountains. By comparing the structure of the model atmospheres that emerged from these two numerical experiments, it is possible to discuss the role of mountains in maintaining the stationary and transient disturbances in the atmosphere. The model adopted for this study has a global computational domain and covers both the troposphere and stratosphere. For the computation of radiative transfer, the distribution of incoming solar radiation in January is assumed. Over the ocean, the observed distribution of the sea surface temperature of February is assumed as a lower boundary condition of the model. Over the continental surface, temperature is determined such that the cond...

Spontaneous Symmetry Breaking in the O(N) Model for Large N

Abstract: We study the O(N) generalization of the σ model in the limit of large N, for four, three, two, and one space-time dimensions. We compute the effective potential and some momentum-dependent Green's functions. In one and two dimensions, spontaneous symmetry breakdown is impossible; any asymmetric minimum inserted in the tree-approximation potential is immediately filled in by the effects of radiative corrections. This is in agreement with general theorems. In four dimensions, the model is inconsistent; it possesses a tachyon. In three dimensions, the model seems to be consistent, and offers an interesting example of some nonlinear effects associated with spontaneous symmetry breakdown that are not present in the usual (tree-approximation) models.

Aerosols and climate.

Abstract: To determine the effects of atmospheric aerosols on the radiative heating of the earth-atmosphere system, the radiative transfer equation is solved analytically in the two-stream approximation. It is found that the sign of the heating is independent of optical thickness of an aerosol layer and the amount of heating approaches a finite limit with increasing thickness of a layer. Limitations of the two-stream approximation are discussed.

Theory of the optical properties of snow

Abstract: The optical properties of a snowpack are calculated, giving relations between the asymptotic flux extinction coefficient and albedo under diffuse illumination on the one hand and the density, grain size, and wavelength, on the other. A geometrical optics calculation of the properties of a single grain is used with approximate solutions of the radiative transfer problem. Most of the scattering is the result of change in direction of the light beam upon transmission through the grain, rather than reflection. The asymptotic flux extinction coefficient is directly proportional to the snowpack density and inversely proportional to the square root of the grain size. The albedo under diffuse illumination is independent of density and proportional to the square root of the grain size. The derived relations agree with experimental data to within 20% for the flux extinction coefficient and to better than 2% for the albedo without using adjustable parameters. Higher values of the flux extinction coefficient will be measured if the snow is confined within a finite cylinder with absorbing sides. An analysis of this effect is given.

Remote Sounding of Cloudy Atmospheres. I. The Single Cloud Layer

Abstract: The relaxation method for the inverse solution of the radiative transfer equation is applied in a dual-frequency scheme for the determination of complete vertical temperature profiles in cloudy atmospheres from radiance observations alone, without any additional information related to the expected solutions. The dual-frequency principle employs to advantage a property in the Planck function of the dependence of intensity on frequency. This property leads to the formulation of a new convergence criterion for the selection of cloud-sounding frequencies to be used for reconstructing the clear column radiance from observations made in the presence of a broken cloud layer in all fields of view. The principle is applied to the case of observations in two adjacent or partially overlapping fields of view and to the case of observations in a single field of view. The solutions are illustrated by numerical examples in the dual-frequency ranges of the 4.3 and 15-micron CO2 bands of the terrestrial atmosphere.

Temperature dependence of the radiative recombination coefficient in silicon

Abstract: The temperature dependence of the intrinsic radiative recombination coefficient B in silicon was measured from 100 to 400 °K. In contrast to previous calculations, B decreases with temperature. For interpretation of the measurements, a unique theory of the indirect radiative band-to-band and free exciton recombination is given. The decrease of B with increasing T is due to the decrease to the exciton concentration and of the Coulomb-enhancement of the band-to-band recombination rate. The latter however is smaller than the exciton recombination part even at room temperature. The constants of the exciton and band-to-band recombination are determined.

Rotation and Rotation-Vibration Pressure-Broadened Spectral Lineshapes

Abstract: The last comprehensive review of rotational spectral lineshapes was by Birn­ baum (1) in 1967. Since then a considerable number of experiments have been performed, providing additional insight into the basic theory of lineshapes. The present review emphasizes developments since the earlier review, although material previous to that is cited when necessary. It is instructive to examine why spectral lineshapes, rotational or otherwise, have received such wide experimental and theoretical interest. The answer en­ compasses both practical and basic physical concerns. For example, the design and operation of gaseous molecular lasers require knowledge of the pressure­ induced widths and shifts of the spectral lines. Engineers interested in radiative transfer in the atmosphere (2,3) need to know the location of the spectral windows and their absorption characteristics. Such energy transmission charac­ teristics can be sensitive to the wings of the atmospheric spectral lines. Studies of pollutants in the atmosphere have also drawn on spectral lineshape data for developing measurement techniques. The necessity for such lineshape data has stimulated research in this area (4, 5). Radiative transfer research has not been restricted to our own atmosphere (6). For example, the widths of CH4 and NH3 lines broadened by CH4 (7-9) are relevant factors in the spectral transmission in the atmosphere of Jupiter. In the absence of direct measurements, the line­ strength of CO and its CO2 broadened width would be helpful for studying the presence of CO in the Martian atmosphere, as pointed out by Tubbs (10). In addition to the above experimental and practical considerations, other research has focused on the analysis of spectral lineshapes in order to study the physical phenomena responsible for the shapes themselves. This is the emphasis

Model calculations for diffuse molecular clouds

Abstract: A steady state isobaric cloud model is developed. The pressure, thermal, electrical, and chemical balance equations are solved simultaneously with a simple one dimensional approximation to the equation of radiative transfer appropriate to diffuse clouds. Cooling is mainly by CII fine structure transitions, and a variety of heating mechanisms are considered. Particular attention is given to the abundance variation of H2. Inhomogeneous density distributions are obtained because of the attenuation of the interstellar UV field and the conversion from atomic to molecular hyrodgen. The effects of changing the model parameters are described and the applicability of the model to OAO-3 observations is discussed. Good qualitative agreement with the fractional H2 abundance determinations has been obtained. The observed kinetic temperatures near 80 K can also be achieved by grain photoelectron heating. The problem of the electron density is solved taking special account of the various hydrogen ions as well as heavier ones.

Pioneer 10 ultraviolet photometer observations at Jupiter encounter

Abstract: A two-channel extreme ultraviolet photometer on Pioneer 10 was used to investigate hydrogen and helium emissions from the atmosphere of Jupiter and emissions associated with the Galilean satellites. The hydrogen Lyman alpha signal observed from Jupiter corresponded to 400 R in brightness. By using the results of Wallace and Hunten (1973), the eddy diffusion coefficient is found to be K = 3 x 10 to the (8 plus or minus 1) power. The He I 584-A emission rate was found to be 5.1 R. The radiative transfer problem for the resonantly scattered He I emissions was investigated in the coherent approximation. With these results, the observed brightness, and the derived eddy diffusion coefficient the He/H2 ratio in the mixing region of the atmosphere was found to be equal to 0.18 minus 0.12 or plus 0.46. Emissions attributed to H I Lyman alpha were found at the orbital radius of Io and appear to be due to resonance scattering by a toroidal cloud of H in orbit around Jupiter.

Properties of Zn‐doped GaN. I. Photoluminescence

Abstract: Zinc in GaN forms an efficient radiative center emitting blue light at 2.86±0.02 eV and acts as a deep acceptor which can make the crystal insulating. A systematic variation of growth conditions shows that an optimization of the photoluminescence efficiency is possible. Under nonoptimal conditions, lower photon energy emission is obtained. A temperature‐dependent competing nonradiative process has an activation energy of 0.33±0.15 eV. The emission peak exhibits a negligible spectral shift with temperature. The response time of the blue photoluminescence is several orders of magnitude slower than the near‐gap transition. It is suggested that the photoluminescence is due to a radiative transition from the conduction band tail to the Zn acceptor levels.

Frequency integration for radiative transfer problems involving homogeneous non-gray gases: The inverse transmission function

Abstract: It is shown that narrow-band frequency integration for radiative-transfer problems, involving homogeneous non-gray gases, can be accomplished by an integration with respect to the absorption coefficient. The kernel of the absorption-coefficient integral is a property of the gas and can be obtained directly from the absorption coefficient for a simple dependence of the absorption coefficient on frequency. It is shown that the kernel (called the ‘inverse transmission function’) can also be obtained as the inverse Laplace transform of the transmission function, without explicit knowledge of the absorption coefficient. The kernel has been obtained using the inverse transmission-function method for two statistical band models: the Goody model and the Malkmus model. The kernel for the Malkmus model offers a simple, accurate, straightforward method for narrow-band frequency integration.

Multiple scattering calculation of the middle ultraviolet reaching the ground.

Abstract: An investigation is conducted regarding the increase in the UV radiation as a function of wavelength due to changes in the amounts of ozone and various other parameters affecting the radiation in the atmosphere. Attention is given to the methods that can be used to solve the problem of the transfer of radiation through an absorbing and scattering atmosphere which includes aerosols. The multiple channel solution reported by Mudgett and Richards' (1971) is extended to vertically inhomogeneous atmospheres.

Radiative transfer due to atmospheric water vapor: Global considerations of the earth's energy balance

Abstract: A simple analytical formulation is presented for describing radiative transfer due to atmospheric water vapor. The radiative model is then applied to a global energy balance for earth, and the net infrared flux to space is expressed in terms of the mean surface temperature and atmospheric lapse rate. Water vapor and clouds are assumed to be the only sources of infrared opacity. When compared with empirical information, and for a global mean surface temperature of 288 K, the radiative model indicates a cloud top altitude for a single effective cloud of 6·8 km. Alternatively, when applied to a more realistic three-cloud formulation, the model predicts a comparable value of 6·5 km for an average cloud top altitude. With respect to changes in mean surface temperature, again comparing with empirical results, a discussion relating to the model suggests that the cloud top altitude decreases with decreasing surface temperature, which results in the surface temperature being roughly twice as sensitive to changes in factors such as planetary albedo than for the conventional assumption of a fixed cloud top altitude. Implications of this are discussed with respect to possible albedo changes due to atmospheric particulate matter as well as cloudiness as a climate feedback mechanism.

Alkali-metal negative ions. I. Photodetachment of Li - , Na - , and K -

Abstract: Photodetachment cross sections of the negative ions of the three lightest alkali-metal atoms have been calculated using configuration-interaction wave functions for the initial state and close-coupling scattering wave functions for the final state. Pronounced structure obtained at the threshold for leaving the neutral atom in the first excited state is due to a combination of real resonance behavior and the threshold law for collisional excitation. The range of validity of this law is, however, found to be very narrow. The shape of the cross sections in this region is in excellent agreement with experimental measurements. Results are also presented for the angular distribution of the photoelectrons following photodetachment with simultaneous neutral excitation, for the dipole polarizabilities of the negative ions, and simple analytic formulas for the radiative attachment coefficients.

The Effects of Radiative Heat Transfer Upon the Melting and Solidification of Semitransparent Crystals

Abstract: Employing the assumptions of one-dimensional energy transfer, equilibrium phase change, and negligible convection in liquid regions, the time-dependent conservation of energy equation is formulated for the general situation of n semitransparent contiguous liquid and solid phases The dimensionless parameters governing phase change are identified and the effects of their variation are ascertained by a finite difference solution of the rigorously formulated energy and radiative transfer equations The chief conclusions of this investigation are that for the range of parameters encountered in the melting and solidification of many optical materials, radiant transfer has a significant effect, and that during solidification, radiation can force the temperature profile within the liquid phase to assume a shape which leads to unstable interfacial growth

Laser measurements of the radiative lifetime of the B2Σ+ state of CN

Abstract: A turnable dye laser was used to measure the radiative lifetime of the individual rotational levels of the B2 Sigma (+) state of CN. The radiative lifetime of the unperturbed rotational levels is 65.6 plus or minus 1.0 nsec. A longer radiative lifetime of 72 plus or minus 1 nsec is observed for the Kaon prime = 4 level of the B state. The measured values of the perturbed and unperturbed levels support the longer lifetimes for the A2 meson pion state of CN. The quenching cross section of the B2 Sigma state of CN is 41 plus or minus 20 Angstroms squared and is independent of the rotational energy of the B state.

Radiative Transfer in Packed Spheres

Abstract: Radiative transfer through a packed bed of microspheres is analyzed on the basis of a new conceptual model, which combines the continuous and discontinuous models in predicting the scattering and absorption properties of packed microspheres. The basic elements of the formulation consist of the determination of the scattering diagram of a unit cell, the optical properties of a series of thin microsphere layers, and the solution of the two-flux equations. Results show a strong dependence of these radiative properties on the particle diameter and emissivity. Qualitative agreement is shown in the comparison of the predictions with existing experimental data.

Radiative charge transfer from H atoms by fast ions

Abstract: The cross section for radiative electron transfer from H atoms to bound states of an incident ion is calculated for velocities much greater than the orbital velocity of the captured electron. It is shown to dominate over the Coulomb-charge-exchange cross section for $Eg9$ MeV per incident nucleon.

On the Radiative Properties of Cirrus in the Window Region and Their Influence on Remote Sensing of the Atmosphere

Abstract: Transmission, emission and reflection characteristics of cirrus clouds in the 800–1200 cm−1 window region are obtained by means of solving the transfer of infrared radiation in the realistic moist and dry model atmospheres. These model atmospheres include the water vapor within, above and below the cirrus clouds which are assumed to be composed of randomly oriented cylinders. Results of the radiation parameters are presented in terms of the geometrical thickness of circus as well as the model atmospheres. The discrepancies between the transmission and emission for flux and those for the vertically emergent intensity are pointed out and discussed. It is shown that the radiative properties of cirrus depend strongly upon the particle concentration. For a typical cirrus with a thickness of 1 km whose concentration is 0.05 cm−3, the intensity transmission is about 0.65 with an emissivity of about 0.35. Further, based upon the theoretical analyses, the reductions in the effective temperature when cirru...