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- Author or Editor: Ronald M. Welch x
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Abstract
Reflected fluxes are calculated for broken cloudiness (i.e., nonplane parallel) as a function of cloud cover, cloud optical depth, solar zenith angle and surface albedo. These calculations extend previous results for broken cloud reflected fluxes over a black surface.
The present study demonstrates that not only radiances but also radiative fluxes over high albedo surfaces may be decreased by the presence of broken cloudiness. Conventional wisdom states that cloud radiances(brightnesses) are always greater than the background. While most cloud retrieval schemes are built around this assumption, it is incorrect for clouds over high albedo surfaces such as found in polar regions. However, the most startling and counterintuitive conclusion of this study is that nonabsorbing finite clouds over a highly reflecting surface will decrease the system albedo. As a result, surface absorption is increased, the result of multiple scattering between surface and cloud layer, controlled by cloud morphology and cloud optical thickness.
A simple parameterization of the effects of cloud contamination upon retrieved albedo is given in terms of solar zenith angle, cloud optical depth, surface albedo, cloud cover, and plane-parallel could albedo. In this way, the effects of broken cloudiness are modeled in terms of easily computed plane-parallel values.
Abstract
Reflected fluxes are calculated for broken cloudiness (i.e., nonplane parallel) as a function of cloud cover, cloud optical depth, solar zenith angle and surface albedo. These calculations extend previous results for broken cloud reflected fluxes over a black surface.
The present study demonstrates that not only radiances but also radiative fluxes over high albedo surfaces may be decreased by the presence of broken cloudiness. Conventional wisdom states that cloud radiances(brightnesses) are always greater than the background. While most cloud retrieval schemes are built around this assumption, it is incorrect for clouds over high albedo surfaces such as found in polar regions. However, the most startling and counterintuitive conclusion of this study is that nonabsorbing finite clouds over a highly reflecting surface will decrease the system albedo. As a result, surface absorption is increased, the result of multiple scattering between surface and cloud layer, controlled by cloud morphology and cloud optical thickness.
A simple parameterization of the effects of cloud contamination upon retrieved albedo is given in terms of solar zenith angle, cloud optical depth, surface albedo, cloud cover, and plane-parallel could albedo. In this way, the effects of broken cloudiness are modeled in terms of easily computed plane-parallel values.
Abstract
A dynamic-numerical model is utilized to study the impact of air pollution on the temperature and wind distributions of the planetary boundary layer. The mathematical model uses a rather complete radiative treatment which comprises the entire solar and infrared spectrum ranging from 0.29 to 100 µm. In the solar spectral range, the absorption by water vapor, nitrogen dioxide and industrial haze is fully accounted for in addition to multiple scattering by air molecules and haze particles. In the spectral region of the strong absorption hands of the infrared emission spectrum, the effect of aerosol is very small and is disregarded. The emissivity method is applied here, allowing full treatment of the overlapping effects of water vapor and carbon dioxide. In the window region, however, the effect of aerosol and water vapor absorption and emission is taken into account in addition to multiple scattering by aerosol particles. The radiative treatment accounts for the influence of relative humidity on the particle distribution function and on the complex index of refraction of the aerosol. The spherical harmonic method is used to handle the scattering problem.
The dynamical part of the analysis consists of the numerical solution of a coupled system of partial differential equations comprising the equation of horizontal mean motion, the thermodynamic equations of the air and the soil, and the transport equations of moisture and pollution. Various models of the exchange coefficient are used to study the impact of model assumptions on the computed distributions of temperature, pollutant material and wind. It is found that the choice of the exchange model is not critical but has some effect on the model computations. The present calculations show that the maximum impact of air pollution on the evolution of temperature and wind profiles is highly significant, thus verifying the previous conclusions of Zdunkowski and McQuage (1972).
Abstract
A dynamic-numerical model is utilized to study the impact of air pollution on the temperature and wind distributions of the planetary boundary layer. The mathematical model uses a rather complete radiative treatment which comprises the entire solar and infrared spectrum ranging from 0.29 to 100 µm. In the solar spectral range, the absorption by water vapor, nitrogen dioxide and industrial haze is fully accounted for in addition to multiple scattering by air molecules and haze particles. In the spectral region of the strong absorption hands of the infrared emission spectrum, the effect of aerosol is very small and is disregarded. The emissivity method is applied here, allowing full treatment of the overlapping effects of water vapor and carbon dioxide. In the window region, however, the effect of aerosol and water vapor absorption and emission is taken into account in addition to multiple scattering by aerosol particles. The radiative treatment accounts for the influence of relative humidity on the particle distribution function and on the complex index of refraction of the aerosol. The spherical harmonic method is used to handle the scattering problem.
The dynamical part of the analysis consists of the numerical solution of a coupled system of partial differential equations comprising the equation of horizontal mean motion, the thermodynamic equations of the air and the soil, and the transport equations of moisture and pollution. Various models of the exchange coefficient are used to study the impact of model assumptions on the computed distributions of temperature, pollutant material and wind. It is found that the choice of the exchange model is not critical but has some effect on the model computations. The present calculations show that the maximum impact of air pollution on the evolution of temperature and wind profiles is highly significant, thus verifying the previous conclusions of Zdunkowski and McQuage (1972).
