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  • Author or Editor: G. M. JURICA x
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G. M. JURICA

Abstract

Brooks' method for computing rates of atmospheric heating which is due to radiation by water vapor has been adapted to the digital computer, allowing investigation of the following aspects of the method: the effect of spacing of data points on heating rate profiles, the dependence of heating rates upon the flux emissivity data, and the influence of the form of the pressure correction factor upon heating rates. Two cases of practical interest have been considered. The first is the effect of radiative heating upon tropospheric temperature inversions. It is concluded, in agreement with the results of Staley, that radiative heating acts to strengthen the inversion when water vapor mixing ratios within the inversion layer are small. The second case studied the consequences of the presence of substantial quantities of water vapor in the stratosphere. Cooling rates ranging up to 2.5° C. day−1 were obtained over a winter cross section of the Northern Hemisphere having a constant relative humidity of 5 perccnt in the stratosphere. Decreases in the net radiative flux, as evidenced by small heating rates in the region of the tropopause at low latitudes, agree with observations by Riehl in the Caribbean and by Kuhn and Suomi in the United States. The fact that this effect was not present when mixing ratios were allowed to decrease rapidly above the tropopause lends support to the argument that substantial quantities of water vapor are present in the stratosphere.

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D. O. Staley and G. M. Jurica

Abstract

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D. O. Staley and G. M. Jurica

Abstract

The effective atmospheric emissivity, F↓/(σT 0 4), where F↓ is the downward radiative flux density and σT 0 4 the blackbody flux density at the surface temperature T 0, is computed for clear skies and straight temperature and dew-point soundings by means of emissivity integrations. Emissivity data by Jurica and by Staley and Jurica were used, and separate computations made for H2O, CO2, H2O-CO2 overlap, and O3. The effective atmospheric emissivity depends almost entirely on surface vapor pressure, decreases slightly with increasing surface elevation, and is essentially independent of surface temperature. The contribution by CO2 decreases from about 0,19 to about 0.17 as surface elevation increases from sea level to 710 mb. The contribution of overlap is negative and increases rapidly with increasing surface vapor pressure, becoming comparable to the CO2 contribution for very large vapor pressures. Measurements support the computations, but suggest, as has been found before, additional downward flux density from aerosols or from as yet unspecified trace gases.

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D. O. Staley and G. M. Jurica

Abstract

Flux emissivities for the H2O bands and window, and for CO2 and O3, were evaluated from Elsasser's wavelength-dependent absorption coefficients and flux tranmissivities. The flux emissivities for water vapor differ significantly from previously published emissivities based on Elsasser's incorrect flux densities. A flux emissivity correction for the overlap of H2O and CO2, is defined and evaluated for combinations of optical depths.

The largest partial emissivity is associated with the H2O rotation band, and it increases markedly with decreasing temperature, while the partial emissivities associated with the 6.3 μ band and the window are smaller and decrease with decreasing temperature. Emissivity in the window increases very rapidly with optical depths ≳1 gm cm−2. The total H2O flux emissivity is remarkably independent of temperature, especially in the range from −40 to 20C, as a result of near cancellation of the temperature dependences in three regions of the spectrum. The total flux emissivity increases rapidly with optical depth beyond ∼1 gm cm−2 as a result of emission in the window. An H2O column with a temperature of 20C is 98% black for optical depths >50 gm cm−2.

The flux emissivity of CO2 increases slightly with temperature at all but the very smallest optical depths. This result traces physically to the increase of absorption with temperature at the edges of the 15 μ band.

The correction to flux emissivity resulting from the overlap of H2O and CO2 radiation is negative and increases markedly with the optical depths of both. It is of the order of −0.05 to −0.10 for typical total atmospheric optical depths. This emissivity correction for overlap shows a large percentage increase with temperature, principally as a result of increasing absorption with temperature in the wings of both the rotation band of H2O and the 15 μ CO3 band.

The flux emissivity of O3 undergoes a large percentage decrease with temperature. For typical total O3 depths, the emissivity for −70C is less than half its value at 20C.

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