Homogeneous Cloud Research Articles

Interpretation of the Photometric Measurements of Venus by Mariner 10

Observations by the television system on Mariner 10 of solar radiation reflected by Venus are analyzed by means of comparisons with theoretical computations. It is found that the distribution of radiance across the planetary disc in blue and orange light cannot be explained by a single homogeneous cloud consistent with polarization measurements. Preliminary work has been done for analysis of the Mariner 10 data with a two-cloud model. It is anticipated that the data will allow the extraction of some knowledge of the variations of the optical thickness of the upper cloud, and of the relectivities of both layers.

Feedback Coupling of Absorbed Solar Radiation by Three Model Atmospheres with Clouds

Abstract A study of the amount of solar radiation absorbed by the earth-atmosphere system as a function of the surface temperature is made comparing three model atmospheres with clouds. The atmospheres are generated as previously reported by Weare and Snell. This involves a quasi-isentropic expansion of moist surface air of given relative humidity. “Rainout” of condensate and the lapse rate are parameterized. The three atmospheres to be compared are a horizontally homogeneous diffuse thin cloud structure, a half-cloud .half-clear structure, and a variable fractional cloud cover, each normalized to give the proper albedo at a reference point representative of global annual average conditions. Radiative transfer calculations are made using the modified two-stream approximation and/or the Eddington approximation. The results indicate that with the diffuse thin cloud the magnitude of the feedback coupling of solar radiation absorbed to surface temperature lies intermediate to that of the other structures, wit...

Venus cloud properties: Infrared opacity and mass mixing ratio

By using the Mariner 5 temperature profile and a homogeneous cloud model, and assuming that CO 2 and cloud particles are the only opacity sources, the wavelength dependence of the Venus cloud opacity is infrared from the infrared spectrum of the planet between 450 and 1250 cm −1. Justification for applying the homogeneous cloud model is found in the fact that numerous polarization and infrared data are mutually consistent within the framework of such a model; on the other hand, dense cloud models are not satisfactory. Volume extinction coefficients varying from 0.5 × 10 −5 to 1.5 × 10 −5 cm −1, depending on the wavelength, are determined at the tropopause level of 6110 km. By using all available data, a cloud mass mixing ratio of approximately 5 × 10 −6 and a particle concentration of about 900 particles cm −3 at this level are also inferred. The derived cloud opacity compares favorably with that expected for a haze of droplets of a 75% aqueous solution of sulfuric acid.

The approximate distribution of scattered solar radiative intensities from optically thin cirrus

The present study deals with the approximate scattering characteristics of optically thin cirrus clouds which are known to exist in the vicinity of the tropopause. The assumed homogeneous ice model cloud is composed of randomly oriented circular cylinders of uniform size. The spectral region investigated extends from 0.6–0.7 μ, where absorption by ice and atmospheric gases is negligible Radiative upward and downward intensities are calculated for a uniform ground albedo of 0 and 0.25 using the assumption that multiple-scattering can be disregarded. A rough comparison with the Rayleigh scattering characteristics in this spectral region indicates that remote sensing of the atmosphere is affected very little by the presence of optically thin cirrus assuming the validity of the above assumptions.

Etude theorique de la repartition de luminance sur le disque de Venus

The analysis of the sunlight scattered by Venus gives some insight upon its clouds. The measurements of polarized light are probably more sensitive to the nature of their constituents, and some recent studies seem to be able to give a satisfactory interpretation of this part of the scattered light. But the polarized light concerns the upper part of the clouds, and it is interesting to compare these results with intensity measurements. The phase curves, for the integrated light, leave some indeterminations, so we have studied if the intensity distribution on the Venus disk could give more accurate informations. This work, based on some plates kindly communicated by A. Dollfus, and analysed at Meudon Observatory, is more a preliminary investigation of the sensitivity of the method than an interpretation of the partial results presented. A simple model, of homogeneous plane parallel cloud, has been used, and the influence of various parameters has been tested (single scattering albedo, refractive index of particles and size distribution, optical depth of the cloud).

On the interpretation of the “inverse phase effect” for CO 2 equivalent widths on Venus

Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO 2 lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus.

Degree and Direction of Polarization of Multiple Scattered Light 1: Homogeneous Cloud Layers

The degree of polarization as well as the direction of the polarization are calculated by a Monte Carlo method for homogeneous layers. Two solar zenith angles and a range of optical thicknesses up to 10 are considered. The results are compared with calculations for single scattered photons. For a given pair of incident and scattered directions, there are only two possible values for the direction of the polarization for single scattering: it must be within or perpendicular to the scattering plane. The choice between these two values depends only on the sign of the element M(-) in the first row and second column of the scattering matrix in the I, Q, U, V representation. In most cases there is little change in the direction of the polarization when multiple scattering is taken into account, so that this quantity with respect to a meridian plane can usually be predicted from a very simple trigonometric relationship to good accuracy. The partial scattering angles at which M- changes sign are unique for a particular aerosol model. Thus different size distributions and indices of refraction can be distinguished by measurements of the direction of polarization.

Astrophysical Masers. I. Source Size and Saturation

view Abstract Citations (155) References (2) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astrophysical Masers. I. Source Size and Saturation Goldreich, Peter ; Keeley, Douglas A. Abstract The relation between the apparent and actual sizes of maser sources is important in determining their internal physical conditions. This relation is investigated for models of homogeneous maser clouds having spherical and tube-shape geometries. It is found that the apparent linear size of a spherical OH or H2O maser may be as much as two orders of magnitude smaller than the physical extent of the emitting cloud. On the other hand, the observed size of a maser having the shape of a thick tube is given by its transverse dimensions. The treatment of maser radiation uses rate equations for the level populations and the ordinary equation of transfer. Approximate analytic calculations are presented for all degrees of saturation. The theory is developed in terms of a multilevel scalar atom in which only two levels are coupled by the maser radiation. Thus, the effects of hyperfine splitting and polarization are ignored. Publication: The Astrophysical Journal Pub Date: June 1972 DOI: 10.1086/151514 Bibcode: 1972ApJ...174..517G full text sources ADS |

Multiple scattering of anisotropic radiation through a layer of clouds

A method by which the transport of anisotropic radiative multiple scattering can be predicted is developed in this paper. A one-dimensional integral intensity model and a three-dimensional diffusion intensity model are both constructed. The former provides a closed-form solution, while the latter involves successive approximation and Gauss's quadrature. On the basis of these methods, the reflection and transmission of solar radiation in a homogeneous cloud layer are computed. The results differ from those for isotropic and Rayleigh scattering assumptions and illustrate the effects on transmission and reflectivity of optical thickness, wavelength, incidence angle, and albedo of single scattering.

The influence of clouds on microwave brightness temperatures viewing downward over open seas

Microwave brightness temperatures for the case of downward viewing from above the earth's atmosphere over water for the 1- to 2-cm wavelength range are calculated for comparison with observations. A model of the troposphere which contains homogeneous layer clouds of varied thickness and liquid water content is used to compute estimates of the influence which clouds would have on real observations. It is assumed that only pure absorption is important for the cloud droplet-size distributions and droplet densities used. Results of the computations indicate that most water clouds will contribute a measurable amount to the microwave emission of the atmosphere and, in some cases, can be the principal source of received radiation. Comparisons of the computed cases with measurements obtained with a high flying aircraft are shown to be in reasonable agreement. These results are significant because they demonstrate that water clouds cannot be neglected in the application of passive microwave techniques to remote probing of the earth's atmosphere and because they indicate that quantitative measures of cloud liquid water contents and cloud thickness might be acquired through multi-frequency measurements.

Theoretical Frequency Averages for the Emittance of a Homogeneous Gas-Particle Cloud*

Frequency averages have been obtained for the one-dimensional-beam emittance of a thick cloud composed of a radiating gas and nonabsorbing particles in the two limits in which scattering or absorption predominate. The models considered are the single Lorentz line with fine Δν and the Elsasser band, for the case β = 2π ( 12 width/spacing) ≪ 1. An approximate method is suggested for connecting these results with the thin cloud and the emittance for arbitrary optical depth and smeared line (β ≫ 1).

Chemical evolution of the terrestrial planets

Chemical evolution of the terrestrial planets

Mass Models of the Galactic System.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass Models of the Galactic System. Innanen, Kimmo A. Abstract Models of the galactic mass distribution have been obtained using Schmidt- type nonhomogeneous spheroids. Values of the distance of the sun from the galactic centre of 8.2 and 10.0 kpc with circular velocities near the sun varying from 200 to 250 km/sec were adopted. Each model reproduces a rotation curve which is the smoothed mean of the Leiden and Sydney 21-cm results, together with the Leiden 21-cm observations of the rotation near the galactic center. The total density near the sun was taken to be 0.15 M~pc3. The principal characteristics of the models have been evaluated with an electronic computer. The models show that the mass in a column of unit area at the sun's position, perpendicular to the plane of the model, increases with increasing circular velocity near the sun. The observed mass perpendicular to the plane near the sun is reproduced if the circular velocity near the sun is approximately 200 km/sec. This low value of the circular velocity makes it unnecessary to introduce unknown matter to the model. The total masses of the models vary between 0.6 and 1.2 x 1011M . All of the models may be modified without significantly changing the results if a considerable fraction of the total mass is distributed in Schmidt- type spheroids with little flattening. A comparison of the models with M31 has been made by tilting them to the apparent attitude of M31, and by obtaining "mass profiles" of the resulting long axes of the tilted models. These profiles may be compared with de Vaucouleurs' (Astrophys. J. 128, 465, 1958) photometry along the long axis of M31. The comparison with the models is very good, confirming the existence of additional mass in the central parts of the galactic system. A comparison has also been made between the angular momentum distributions of the models and that of a uniformly rotating, homogeneous spheroidal gas cloud, following the method of Crampin and Hoyle (Astrophys. J. 140, 99, 1964). The comparisons are good and thus tend to confirm the conclusion that the galactic system may have collapsed from such a cloud, without turbulent mixing. Publication: The Astronomical Journal Pub Date: March 1965 DOI: 10.1086/109693 Bibcode: 1965AJ.....70..141I full text sources ADS |

On the Fragmentation of Self-Gravitating Gas Clouds.

view Abstract Citations (72) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Fragmentation of Self-Gravitating Gas Clouds. Layzer, David Abstract Much of current cosmogonic thinking is based on the idea that a more or less homogeneous, selfgravitating gas cloud can, under appropriate conditions, break up into a collection of seff-gravitating subsystems. Attempts to justify this idea theoretically have usually employed linearized stability theory. This paper shows, however, that the stability of a more or less homogeneous cloud against fragmentation hinges, in fact, on certain non4inear processes. A semi-quantitative treatment of these processes lends strong support to the conclusion that fragmentation cannot occur under circumstances likely to be realized in nature. The paper also points out that fragmentation is not the only available hypothesis on which to base theories for the formation of stars and galaxies and shows, by means of an example, that the difficulties confronting the fragmentation hypothesis are avoidable. Publication: The Astrophysical Journal Pub Date: February 1963 DOI: 10.1086/147515 Bibcode: 1963ApJ...137..351L full text sources ADS |

An Improved Spinning Top Homogeneous Spray Apparatus

An apparatus is described which produces homogeneous mists or clouds of solid particles of any desired size. As in Walton's original model liquid is sprayed by a Beams high speed air-driven top, but an improved performance has been achieved by utilizing a property of high speed air films so that automatic extraction of unwanted satellite droplets, better running characteristics over a wider range, simplified construction, and low air consumption are obtained.

The Production of Sprays and Mists of Uniform Drop Size by Means of Spinning Disc Type Sprayers

Spray of almost uniform drop size is formed when liquid is fed under suitable conditions on to the centre of a rotating disc and centrifuged off the edge. This method of spraying has been studied over a wide range of variables and homogeneous clouds have been produced in the drop-size range from 3 mm. to 15 μ diameter. The size of the spray drops is given approximately by the equation d=3.8 (T/Dρ)½/ω where d=drop diameter, D=disc diameter, ω=angular velocity of disc, T=surface tension of liquid, ρ=density of liquid. The spray thus formed also contains a proportion of fine satellite drops, but their smaller distance of projection from the disc enables them to be removed from the cloud when their presence is undesirable. Relatively coarse sprays are easily produced by means of a simple electric motor-driven disc. The finer spray sizes require rotor speeds up to several thousands of revolutions per second and high speed air driven "tops" have been used for this purpose. Suitable designs of apparatus are described.