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Lewis D. Kaplan

Abstract

Recent experimental evidence seems to establish the validity of Lorentz (linear) pressure broadening of spectral lines under atmospheric conditions. This simplifies the analytical representation of the fractional transmission by atmospheric layers in which the pressure decreases with height.

A transmission function is derived and tabulated, with use of the Elsasser assumption of lines of equal intensity and equal spacing. It is found that further approximations made in the construction of the Elsasser diagram result in overestimation of cooling rates with its use.

Stratospheric heating and cooling rates caused by carbon dioxide are calculated for the N.A.C.A. Standard Atmosphere. Considerable radiative-flux divergence is found in the 15-µ band.

Neglect of the pressure effect has resulted in underestimation of outgoing radiation by previous investigators of the heat balance. Thus a smaller value of the albedo is required, in agreement with Fritz's findings.

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Lewis D. Kaplan

Abstract

An atmospheric transmission function is derived for spectral lines of arbitrary line intensities and line spacing. It is shown that the variability of the exponent occurring in this and other atmospheric transmission functions can be taken into account by an arithmetical averaging of the mixing-ratio–line-intensity factor over pressure intervals as large as 100 mb. Elsasser's suggestion of a constant factor to convert parallel-beam transmission to diffuse transmission appears to be justified. Energy-transfer considerations indicate a factor of 1.60.

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Lewis D. Kaplan

Abstract

The energy transfer between air layers, and that between an air layer and black surface, are examined for a schematic rotation-vibration band of a gas whose mixing ratio decreases with height. It is found, in general, that most transfer is due to the central portions of moderately weak lines. Small errors in transmission functions may lead to large errors in energy transfer, especially in the upper half of the atmosphere. This is particularly true of the “black line-center” approximation.

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Lewis D. Kaplan

Abstract

Elsasser's integral for the absorption by a periodic line pattern is evaluated and used to examine the validity of various approximations concerning the absorption coefficient. It is found that composite absorption curves, obtained by ignoring overlapping for small optical paths and ignoring the pressure-dependent term in the denominator of the expression for the absorption coefficient for large optical paths, may be applicable to calculation of radiative heat transfer in the atmosphere.

It is shown that the theoretical prediction of the “square-root law” of absorption is based on use of approximations that are particularly invalid for the cases for which the “law” is supposed to be valid. An explanation is given for the apparent experimental verification of this “law”.

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Lewis D. Kaplan

Abstract

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Stephen B. Fels and Lewis D. Kaplan

Abstract

The dynamical consequences of systematic changes in longwave radiative transfer computations have been investigated using the NCAR six-layer General Circulation Model. The experiments were run for a period of 40 days each: the “control” case with an emissivity computation, and the “test” case using a 19-sepctral-interval calculation, in which the Curtis-Godson approximation is employed. The two calculations lead to substantially different cooling rates when applied to identical soundings, especially in the tropics.

Significant differences are observed in the thermal structure of the two cases, and in the mean meridonal circulations. The total kinetic energy is somewhat higher in the test case, probably due to increased baroclinic activity in latitudes.

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