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Frederick M. Luther

Abstract

An analytic expression for the specific heating rate due to solar absorption by nitrogen dioxide is derived by approximating the solar insolation and absorption cross section by simple functions of wavelength. The analytic expression agrees with a detailed calculation to within ±2 × 10−22 W throughout the range of NO2 column densities investigated (up to 1020 cm−2). The error is within ±0.3% for NO2 column densities less than 2 × 1017 cm−2. The error is generally within ±5% for the larger column densities which rarely, if ever, occur in the atmosphere.

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Frederick M. Luther

Abstract

The solar and longwave radiative effects of a stratospheric aerosol layer between 18 and 22 km are compared for a tropical atmosphere. The changes in the daily mean solar and longwave radiative fluxes above and below the aerosol layer are computed for two particle size distributions and as a function of the albedo of the earth's surface. The changes in the solar and longwave fluxes above the aerosol layer are found to be comparable in magnitude. In the troposphere, the reduction in the incoming solar radiation (cooling) is several times greater than the increase in the downward longwave radiation (warming), the difference decreasing with increasing surface albedo.

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Joyce E. Penner
and
Frederick M. Luther

Abstract

Calculated perturbations to stratospheric ozone are generally thought to be reduced when temperature feedback is included in the model. We find that when self-consistent hydrostatic adjustment is included with temperature feedback, there can be significant differences in the computed change in local ozone concentration. We present results in two frames of reference (changes in ozone at constant altitude and changes at constant pressure) to illustrate the importance of the frame of reference. Including hydrostatic adjustment is particularly important for calculations of the change in local ozone at constant altitude due to CFM, CO2 and H2O perturbations because large changes in the temperature structure are predicted. Only small differences are computed for increases in N2O. Air density adjustment in a constant pressure frame of reference is important when local temperature changes are large.

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Frederick M. Luther
and
Benjamin M. Herman
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Frederick M. Luther
,
Robert G. Ellingson
,
Yves Fouquart
,
Stephen Fels
,
Noelle A. Scott
, and
Warren J. Wiscombe

An international program of intercomparison of radiation models has been initiated because of the central role of radiative processes in many proposed climate change mechanisms. Models ranging from the most detailed (line-by-line) to the most-highly parameterized have been compared with each other and with selected aircraft observations. Although line-by-line-model fluxes tend to agree with each other to within one percent (if the water-vapor–continuum absorption is ignored), the less-detailed models show a spread of 10–20 percent. The spread is even larger (30–40 percent) for the sensitivities of the models to changes in important radiation variables, such as carbon dioxide amounts and water-vapor amounts. These spreads are disturbingly large.

Lacking highly accurate flux observations from within the atmosphere, it has been customary to regard line-by-line–model results as “the truth.” However, uncertainties in the physics of line wings and in the proper treatment of the water-vapor continuum make it impossible for the line-by-line models to provide an absolute reference for evaluating less-detailed models. Therefore, a dedicated surface-based field measurement program is recommended in order to properly evaluate model performance; the goal would be to use sophisticated spectrometers to measure accurately spectral radiances rather than integrated fluxes.

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