Engineering topics

Toon, O. B.

Publications and source records attributed to Toon, O. B..

138 records · Page 8

NASA NTRS1976

A global average model of atmospheric aerosols for radiative transfer calculations

A global average model is proposed for the size distribution, chemical composition, and optical thickness of stratospheric and tropospheric aerosols. This aerosol model is designed to specify the input parameters to global average radiative transfer calculations which assume the atmosphere is horizontally homogeneous. The model subdivides the atmosphere at multiples of 3 km, where the surface layer extends from the ground to 3 km, the upper troposphere from 3 to 12 km, and the stratosphere from 12 to 45 km. A list of assumptions made in construction of the model is presented and discussed along with major model uncertainties. The stratospheric aerosol is modeled as a liquid mixture of 75% H2SO4 and 25% H2O, while the tropospheric aerosol consists of 60% sulfate and 40% soil particles above 3 km and of 50% sulfate, 35% soil particles, and 15% sea salt below 3 km. Implications and consistency of the model are discussed.

Toon, O. B.↗

NASA NTRS1976

Estimates of the climatic impact of aerosols produced by Space Shuttles, SST's, and other high flying aircraft

Solar and terrestrial radiative transfer calculations are performed to evaluate the effect of additional aerosols (sulfuric acid, aluminum oxide) produced by aircraft and Space Shuttles flying through the stratosphere on the global heat balance. The results are presented by plotting the dependence of various quantities of interest as a function of the change in the optical depth of the stratosphere at a reference wavelength of 0.55 micron. Perturbation optical depths that will result from the amount of emission expected from supersonic transports (SSTs) and Space Shuttles over the next several decades are determined. The magnitude and importance of the surface temperature change resulting from the added aerosols are assessed. The effect of added aerosols on ozone destruction is evaluated. It is shown that the aerosols produced by SSTs, other high flying aircraft, and Space Shuttles over the next several decades would not seriously alter the climate. However, the effect of SSTs is sufficiently close to the threshold limit, which requires reevaluation as new data are available.

Pollack, J. B.↗

NASA NTRS1976

Volcanic explosions and climatic change - A theoretical assessment

A theoretical assessment is presented of the influence of volcanic activity on the climate. The methodology of radiative transfer calculations is described and the sources of the adopted parameters are considered. The dependence of various quantities of interest is plotted as a function of the change in the optical depth of the stratosphere at a reference wavelength. An investigation is conducted concerning the increase in optical depth produced by volcanic explosions. An estimate is obtained regarding the magnitude of the mean surface temperature change resulting from the added aerosols.

Pollack, J. B.↗

NASA NTRS1975

Solar luminosity variations and the climate of Mars

A simple climatological model of Mars indicates that its climate may be more sensitive to luminosity changes than earth's because of strong positive feedback mechanisms at work on Mars. Mariner 9 photographs of Mars show an abundance of large sinuous channels that point to an epoch of higher atmospheric pressures and abundant liquid water. Such an epoch could have been the result of large-scale solar luminosity variations. The climatological model suggests that other less controversial mechanisms, such as obliquity or polar albedo changes, also could have led to such an epoch.

Toon, O. B.↗

NASA NTRS1975

The effect of volcanic activity on climate

Radiative transfer calculations of the global energy balance were performed to estimate the change in mean surface temperature that results from the addition of volcanic aerosols to the stratosphere. Results of the calculations are consistent with stratospheric warming observed in the last few months following the eruption of Mt. Agung and the average surface temperature decrease found for the two year period following major volcanic explosions.

Pollack, J. B.↗

NASA NTRS1975

Climatic change on Mars and Earth

Work on climatic changes of Mars is reviewed and related to terrestrial problems. In particular the dust storms of Mars are discussed since these represent the only global climatic change which has been scientifically observed. The channels of Mars have provoked studies of climatic change and these are summarized together with polar laminae as a climatic change indicator.

Toon, O. B.↗

NASA NTRS1974

Solar luminosity variations and the climate of Mars

Attempts to resolve the solar neutrino flux problem have led to suggestions of large scale oscillations in the solar luminosity on a geological time scale. A simple climatological model of Mars indicates that its climate may be much more sensitive to luminosity changes than the earth's because of strong positive feedback mechanisms at work on Mars. Mariner-9 photographs of Mars show an abundance of large sinuous channels that point to an epoch of higher atmospheric pressures and abundant liquid water. Such an epoch could have been the result of large-scale, solar luminosity variations. However, our climatological model suggests that other less controversial mechanisms, such as obliquity or polar albedo changes, also could have led to such an epoch. As more becomes known about Mars, it may prove possible to formulate a history of Martian climate. By discovering effects that cannot be due to other mechanisms one may be able to form a chronology of solar luminosity variations to compare with data from the earth.

Toon, O. B.↗

NASA NTRS1974

A study of the effect of stratospheric aerosols produced by SST emissions on the albedo and climate of the earth

Hypothesized fleets of supersonic aircraft, flying at stratospheric altitude, may lead to a significant increase in the aerosol population of the stratosphere. Exact multiple scattering calculations have been carried out to determine the response of the earth's albedo to an increase of the stratospheric aerosol optical depth. It is found that a tripling of the aerosol population in the stratosphere, which represents an extreme upper limit to the effects of SST's, results in a 0.6% increase of the earth's reflectivity and a decrease of the mean surface temperature on the order of 0.3 K. Such changes could be marginally significant.

Pollack, J. B.↗

NASA NTRS1973

Atmospheric pressure variation and the climate of Mars

If Mars has permanent CO2 polar caps, atmospheric heat transport may cause the atmospheric pressure to be extremely sensitive to variations of solar heating at the poles. This could happen because atmospheric heating depends on density, which depends strongly on the polar temperature through the vapor pressure relation. A simple climatological model is used to study the question.

Gierasch, P. J.↗

NASA NTRS1973

Physical properties of the stratospheric aerosols

A comparison of the equilibrium vapor pressure over nitric acid solutions with observed water and nitric acid partial pressures in the stratosphere implies that nitric acid cannot be present as an aerosol particle in the lower stratosphere. A similar comparison for sulfuric acid solutions indicates that sulfuric acid aerosol particles are 75% H2SO4 by weight in water, in good agreement with direct observations. The freezing curve of H2SO4 solutions requires that the H2SO4 aerosol particles be solid or supercooled. The equilibrium vapor pressure of H2SO4 in the stratosphere is of the order of 20 picotorr. At stratospheric temperatures, ammonium sulfate is in a ferroelectric phase. As a result, polar molecules may form a surface coating on these aerosols, which may be a fertile ground for further chemical reaction.

Toon, O. B.↗

NASA NTRS1973

Climatic change on Mars.

It is pointed out that Mars is the only known planet with a major atmospheric constituent condensable at typical surface temperatures. The temperatures range from 290 K at equatorial noon to a temperature at the cold pole of 145 K in polar winter. There may be three different periods of climatic variation on Mars. Aspects of reversible climatic instability might possibly explain the channels and other features suggestive of the extensive occurrence of liquid water on Mars. An aqueous epoch on Mars would have important biological and other geological implications. Putative Martian organisms which flourish in the aqueous epoch may now be in cryptobiotic repose.

Sagan, C.↗

NASA NTRS1973

Optical properties of some terrestrial rocks and glasses.

The optical constants of five naturally occurring rocks have been determined in the spectral range between 0.2 and 50 microns. Between 0.2 and 5 microns, the real and imaginary parts of the index of refraction were found from a combination of reflectivity and transmission measurements by using Beer's law and the Fresnel reflectivity equation. At wavelengths beyond 5 microns, only reflectivity measurements could be made and both constants were found from an application of classical dispersion theory.

Pollack, J. B.↗