[en] This progress report discusses the Science Team participation in the Atmospheric Radiation Measurement (ARM) Program for the period of October 31, 1992 to November 1, 1993. This report summarized the research accomplishments of six papers

[en] Model calculations of the climatic impact of the increasing atmospheric carbon dioxide (CO₂) concentration consistently suggest that a doubling of the CO₂ concentration would lead to a warming of global average surface air temperatures by as much as several degrees Celsius. In this appendix, this controversy about the effect of CO₂ on climate is reviewed. Because the surface energy balance approach to estimating climate sensitivity has been the source of much of the controversy, a review of this approach is presented. It is shown that prior applications of this approach violate the law of conservation of energy (the first law of thermodynamics); therefore, these results are incorrect. Empirical data indicating the relationship between atmospheric emittance and surface vapor pressure and surface air temperature are shown to be consistent with climate model calculations. Consequently, it is not the experimental data that are the basis of the controversy, but rather the analysis and interpretation of these data

[en] To evaluate the possible influence of natural background tropospheric aerosols upon the earth's present climate, we have incorporated aerosol radiation models for continental and maritime aerosols into the Lawrence Livermore National Laboratory statistical-dynamical climate model. The model results suggest that background tropospheric aerosols produce 3⁰-4⁰C global surface cooling, with maximum cooling occurring at high latitudes, results which are essentially consistent with an energy balance climate model study by Coakley et al. (1983). To specifically delineate effects caused directly by the aerosols, as opposed to indirect effects resulting from aerosol-induced climate change, a second climate perturbation was considered that consisted of reducing the solar constant so as to give exactly the same initial reduction in surface-atmosphere solar absorption as for the inclusion of tropospheric aerosols. These separate climate perturbations produced nearly identical climate feedback effects, together with similar changes in atmospheric stability and hydrological cycle, despite the fact that the two perturbations have quite different latitudinal and vertical distributions. This finding is consistent with a general circulation model study by Manabe and Wetherald (1980) concerning perturbations of both atmospheric CO₂ and the solar constant. A related conclusion is that the model's climate response to tropospheric aerosols is insensitive to the manner in which the aerosols are vertically distributed

[en] We report room-temperature laboratory studies of the red bands of methane at 40 different pressure--path-length combinations, corresponding to column densities between 0.024 and 3.897 km-amagat with pressures ranging between 0.10 and 2.00 atm. Detailed equivalent width measurements were used to determine curves of growth and integrated band strengths for the bands at 6190, 6825, 7050, and 7250 A. These measurements confirm the pressure independence of the methane curves of growth found by Lutz, Owen, and Cess for the blue-green bands and can be described by the same numerical curve of growth

[en] Cloud-climate interactions are one of the greatest uncertainties in contemporary general circulation models (GCMs), and this study has focused on one aspect of this. Specifically, combined satellite and near-surface shortwave (SW) flux measurements have been used to test the impact of clouds on the SW radiation budgets of two GCMs. Concentration is initially on SW rather than longwave (LW) radiation because, in one of the GCMs used in this study an SW radiation inconsistency causes a LW inconsistency. The surface data consist of near-surface insolation measured by the upward facing pyranometer at the Boulder Atmospheric Observatory tower. The satellite data consist of top of the atmosphere (TOA) albedo data, collocated with the tower location, as determined from the GOES SW spin-scan radiometer. Measurements are made every half hour, with hourly means taken by averaging successive measurements. The combined data are for a 21-day period encompassing 28 June through 18 July 1987 and consist of 202 combined albedo/insolation measurements

[en] The Oregon State University/Lawrence Livermore National Laboratory general circulation model has been employed as a vehicle for suggesting and exploring various means of converting narrow-band measurements of reflected solar radiation from the earth-atmosphere system to broad-band quantities. For purely illustrative purposes we have adopted, within the model's solar radiation routine, a narrow-band filter function consisting of a square-wave window extending from 0.5 to 0.9 μm. A limitation of the model, for this sort of endeavor, is that is does not include the wavelength dependence of surface albedos. Nevertheless, the model simulations tend to mimic the calibration of a narrow-band instrument, utilizing reflected solar radiation from the earth-atmosphere system as simultaneously measured by a collocated broad-band instrument; for the model, however, this is done in terms of fluxes, in contrast to instrument-measured radiances. The model results suggest that it might be preferable to perform narrow- to broad-band conversions in terms of planetary albedo (or an equivalent quantity), rather than in terms of reflected fluxes or radiances. Further improvement is achieved if, for instruments that can differentiate between clear and overcast conditions, separate clear and overcast calibrations are performed

[en] Using our curve-of-growth measurements in the reduction of planetary observations, we find methane abundances in the atmospheres of Jupiter and Saturn to be between a factor of 3 and 4 larger than previously accepted values based on the analysis of the 3ν₃ band at 1.1 μ, while the amount on Titan is significantly less than that obtained from an analysis of 3ν₃ with the assumption of a pure methane atmosphere. The present results, when combined with the 3ν₃ analysis, suggest a surface pressure on Titan of at least 0.4 atm. Extrapolation of these laboratory data to the observations of Uranus and Neptune lead to single air mass column densities of 5.8 and 7.6 km-am of methane, respectively

[en] The climatic effects of increased atmospheric CO₂ are discussed in the context of the effect upon two basic components of the climate sytem, namely, (1) latitudinal and seasonal radiative heating of the surface-troposphere system and (2) the enhancement of latitudinal and seasonal surface temperatures. Radiative transfer model calculations show that the radiative heating of the surface-troposphere system (caused by increased CO₂) undergoes substantial latitudinal and seasonal variations. The seasonal variations are most pronounced at high latitudes. The increased CO₂ heating of the surface and troposphere is significantly different for clear sky and overcast sky conditions. These CO₂ heating calculations were then incorporated within a seasonal energy balance climate model for the northern hemisphere. Despite the significant seasonal variations in surface-troposphere heating due to increased CO₂, the seasonal model results, when annually averaged over all latitudes, yield essentially the same CO₂-induced increase in hemispherical mean surface temperature as does an annual energy balance model. The seasonal model, however, shows a strong seasonal variation at high latitudes for the increase in zonal surface temperature due to increased atmospheric CO₂. For example, the CO₂-induced enhancement in the zonal surface temperature for 80 ⁰--90 ⁰N is more than 3 times as great in the summer as in the winter

[en] Whether C0₂-H₂0 in a weakly reducing atmosphere could have caused a change in the early Earth's temperature by the so-called 'greenhouse effect' is discussed here. (author)

[en] Considerable differences exist within the literature concerning the effect of volcanically induced stratospheric aerosols upon the earth's planetary albedo. In order to investigate these discrepancies the authors have developed a two-stream approximation which is shown to be in good agreement with more detailed calculations. The model employs aerosol radiative properties which are determined from a separate Mie scattering calculation. Systematic changes are then made within the model to illustrate the individual effects of Rayleigh scattering, the angular dependence of both Rayleigh and aerosol scattering, and full-flux versus single-wavelength calculations. When all interactive effects are included, the aerosol influence upon planetary albedo is reduced relative to the single wavelength calculations, by more than a factor of two. This finding resolves the aforementioned discrepancies. (Auth.)