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Toon, O. B.

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

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Aircraft NO/x/ emissions and stratospheric ozone reductions - Another look

New estimates for stratospheric ozone perturbations attributable to supersonic transport (SST) emissions are presented. First, a review is given of recent data pointing to lower OH concentrations below 30 km, as compared to the values predicted by photochemical models. The evidence for lower OH comes from a wide range of laboratory and atmospheric studies. The sensitivity of theoretical estimates of ozone change to OH abundances, and the coupling mechanisms between the O(x)-NO(x)-HO(x)-Cl(x) families which are responsible for the sensitivity, are discussed. Updated calculations for SST-induced ozone alterations are compared with older predictions. For example, assuming continuous aircraft injection of NO2 at 20 km at a rate of 1 x 10 to the 9th kg per year (globally), a 4% ozone decrease, is now calculated where earlier a 3% ozone increase was found. This large variance from previous forecasts suggests that new assessments of certain other polluting agents, particularly nitrogen fertilizers, are needed.

Turco, R. P.↗
NASA NTRS1981

Implications of stratospheric aerosol measurements for models of aerosol formation and evolution

Calculations of the distribution of stratospheric sulfur gases and of stratospheric aerosols are compared with measurements obtained in Alaska during July 1979. Generally, the measurements are reasonably consistent with the model results. COS is the major sulfur-bearing gas in the stratosphere while CS2 plays a lesser role in the formation of sulfate aerosols. Ammonia, which earlier measurements suggested was a major aerosol constituent, is found to be a contaminant, so models without ammonia chemistry may be justified. The model and the measurements suggest that stratospheric sulfuric acid aerosols nucleate just above the tropopause, but they are older and have grown to larger sizes at higher altitudes.

Toon, O. B.↗
NASA NTRS1981

Radiative properties of the background stratospheric aerosols and implications for perturbed conditions

A series of Mie scattering calculations has been performed to define the wavelength-dependent, single scattering properties of aerosols present in the stratosphere during July 1979. Additional radiative transfer computations were conducted to assess the impact of aerosols on the earth's radiation budget. For these purposes, an extensive set of measurements of aerosol characteristics that were obtained in Alaska from aircraft and satellite platforms was used. At that time, the optical depth was too small for aerosols to significantly impact earth's climate. But the optical depth of the stratospheric aerosol layer has been large enough during some volcanically perturbed periods for the aerosols to have caused a noticeable warming of the stratosphere and cooling of the troposphere.

Pollack, J. R.↗
NASA NTRS1981

Particles above the tropopause - Measurements and models of stratospheric aerosols, meteoric debris, nacreous clouds, and noctilucent clouds

An outline is presented of the present status of knowledge of stratospheric aerosols, meteoric debris, nacreous clouds, and noctilucent clouds. Considerable progress has been made in studies of these particles during the previous decade and it is appropriate to synthesize the information to provide a background for studies planned for the 1980s. Numerical models of the formation, growth, and evolution are considered and a description is given of the physical processes involved, taking into account aspects of nucleation, coagulation, condensational growth, sedimentation, and questions of dynamical transport. A schematic outline of the physical and chemical processes included in a model of stratospheric aerosols is provided.

Toon, O. B.↗
NASA NTRS1981

Large ozone perturbations caused by the 1908 Tunguska meteor fall - Were there related weather effects

The magnitude of the ozone depletion due to the 1908 Tunguska meteor fall is estimated and observational evidence of such a depletion is presented. Calculated stratospheric ozone and NO(x) perturbations caused by the meteor are shown, with the hemispherically averaged model giving total stratospheric ozone reductions as large as 45 percent in the first year, with significant reductions persisting for at least three more years. Ozone depletion above 10 km altitude is found to be about 85 percent for several months, and higher yet at 20, 30, and 40 km. Data from the early 1900s to calculate the variability of the solar constant is used to calculate the ozone column concentration for 1909-11. The results are in close agreement with the model prediction. Weather records of the early 1900s show a cooling trend in the Northern Hemisphere for almost a decade after Tunguska.

Turco, R. P.↗
NASA NTRS1980

Distribution and source of the UV absorption in Venus' atmosphere

The model predictions were compared with the Pioneer Venus probes and orbiter to determine the composition of the UV absorbing materials. The simulations were carried out with radiative transfer codes which included spacecraft constraints on the aerosol and gas characteristics in the Venus atmosphere; gaseous SO2 (a source of opacity at the wavelengths below 0.32 microns), and a second absorber (which dominates above 0.32 microns) were required. The UV contrast variations are due to the optical depth changes in the upper haze layer producing brightness variations between equatorial and polar areas, and to differences in the depth over which the second UV absorber is depleted in the highest portion of the main clouds.

Pollack, J. B.↗
NASA NTRS1980

Greenhouse models of Venus' high surface temperature, as constrained by Pioneer Venus measurements

Recent measurements conducted from the Pioneer Venus probes and orbiter have provided a significantly improved definition of the solar net flux profile, the gaseous composition, temperature structure, and cloud properties of Venus' lower atmosphere. Using these data, we have carried out a series of one-dimensional radiative-convective equilibrium calculations to determine the viability of the greenhouse model of Venus' high surface temperature and to assess the chief contributors to the greenhouse effect. New sources of infrared opacity include the permitted transitions of SO2, CO, and HCl as well as opacity due to several pressure-induced transitions of CO2. We find that the observed surface temperature and lapse rate structure of the lower atmosphere can be reproduced quite closely with a greenhouse model that contains the water vapor abundance reported by the Venera spectrophotometer experiment. Thus the greenhouse effect can account for essentially all of Venus' high surface temperature. The prime sources of infrared opacity are, in order of importance, CO2, H2O, cloud particles, and SO2, with CO and HCl playing very minor roles.

Pollack, J. B.↗
NASA NTRS1980

The astronomical theory of climatic change on Mars

The response of Martian climate to changes in solar energy deposition caused by variations of the Martian orbit and obliquity is examined. A systematic study is presented of the seasonal cycles of carbon dioxide, water, and dust to provide a complete picture of the climate for various orbital configurations. A new theory for the formation of the polar laminae is developed on the basis of this systematic examination. For the present orbital configuration and climate of Mars, it is shown that regolith damping of the seasonal CO2 cycle is unlikely; the mean atmospheric pressure is probably in equilibrium with the regolith; the low albedo of the north H2O polar cap can be explained by an admixture of 85% ice and 15% dust; and the albedo of the polar caps and the polar heat budget are very sensitive to small variations in dust deposition.

Toon, O. B.↗
NASA NTRS1980

On the relationship between secular brightness changes of Titan and solar variability

Titan's geometric albedo varied noticeably from 1972 to 1978, in phase with variations in solar activity (Lockwood and Thompson, 1979). A series of radiative transfer and aerosol formation calculations were made to demonstrate the feasibility of the following scenario for these secular brightness changes. Solar activity changes, especially in the UV output of the sun, result in alterations to the mass production rate of aerosols in Titan's atmosphere, which lead to modifications of their microphysical properties. The latter, in turn, cause the albedo to vary. Current estimates of the change in the solar UV radiation below the dissociation limit of methane imply alterations to the mean radius of the aerosols over an 11-yr solar cycle that are consistent in sign and magnitude with those required to explain the observed secular brightness changes.

Pollack, J. B.↗
NASA NTRS1980

A physical model of Titan's clouds

A physical model of the formation and growth of aerosols in the atmosphere of Titan has been constructed in light of the observed correlation between variations in Titan's albedo and the sunspot cycle. The model was developed to fit spectral observations of deep methane bands, pressures, temperature distributions, and cloud structure, and is based on a one-dimensional physical-chemical model developed to simulate the earth's stratospheric aerosol layer. Sensitivity tests reveal the model parameters to be relatively insensitive to particle shape but sensitive to particle density, with high particle densities requiring larger aerosol mass production rates to produce compatible clouds. Solution of the aerosol continuity equations for particles of sizes 13 A to about 3 microns indicates the importance of a warm upper atmosphere and a high-altitude mass injection layer, and the production of aerosols at very low aerosol optical depths. Limits are obtained for the chemical production of aerosol mass and the eddy diffusion coefficient, and it is found that an increase in mass input causes a decrease in mean particle size.

Toon, O. B.↗
NASA NTRS1980

Atmospheric aerosols and climate

The impact of terrestrial aerosols on the earth's climate and solar and infrared radiation budget are considered. Attention is given to the optical properties of aerosols, that is, optical depth, the single scattering albedo, and the asymmetry parameter, and to the relation between the optical depth and surface temperature for tropospheric and stratospheric aerosols. Also considered are experimental projects to determine the single scattering albedo, as well as the optical properties of natural aerosols such as sea salt, soil, and sulfates, and their variability. In addition, the impact of volcanic activity and the question of whether aerosols cause climatic warming or cooling are discussed, and the available observational evidence linking aerosols and climate is reviewed.

Toon, O. B.↗
NASA NTRS1980

Smoke and dust particles of meteoric origin in the mesosphere and stratosphere

A height profile of ablated mass from meteors is calculated, assuming an incoming mass of 10 to the -16th g/sq cm/s (44 metric tons per day) and the velocity distribution of Southworth and Sekanina, which has a mean of 14.5 km/s. The profile peaks at 84 km. The fluxes of micrometeorites and residual meteoroids are also calculated. The coagulation of the evaporated silicates into 'smoke' particles is then followed by means of a model adapted from a previous study of the stratospheric sulfate layer. Numerous sensitivity tests are made. Features of the results are a sharp cutoff of the particle distribution above 90 km, and a surface area close to 10 to the -9th sq cm/cu cm all the way from 30 to 85 km. Some confirmation is obtained from balloon studies of condensation nuclei, although the various measurements differ greatly. The optical scattering and extinction are shown to be undetectable. Several potential applications are suggested: nucleation of sulfate particles and noctilucent clouds, scavenging of metallic ions and atoms, and perhaps other aeronomical effects. The latter are limited to processes that can be influenced by a collision time of the order of a day.

Hunten, D. M.↗
NASA NTRS1980

OCS, stratospheric aerosols and climate

The carbonyl sulfide budget in the atmosphere is examined, and the effects of stratospheric sulfate aerosol particles, formed in part from atmospheric carbonyl sulfate, on global climate are considered. From tropospheric measurements of carbon disulfide and the rate constant for the conversion of carbon disulfide to carbonyl sulfide, it is estimated that five Tg of carbonyl sulfide/year could be generated from carbon disulfide in the atmosphere. Direct sources of OCS include the refining and combustion of fossil fuels (1 Tg/year), natural and agricultural fires (0.2 to 0.3 Tg/year), and soils (0.5 Tg/year), yielding a total influx of from 1 to 10 Tg/year, up to 50% of which may be anthropogenic. Considerations of carbonyl sulfide sinks and concentrations indicate an atmospheric lifetime of one year, with OCS the major atmospheric sulfur compound. It is estimated that a ten-fold increase in atmospheric carbonyl sulfide would cause an optical depth perturbation comparable to that of a modest volcanic eruption, leading to an average global surface temperature decrease of 0.1 K, in addition to a possible greenhouse effect.

Turco, R. P.↗
NASA NTRS1980

Stratospheric aerosol modification by supersonic transport operations with climate implications

The potential effects on stratospheric aerosois of supersonic transport emissions of sulfur dioxide gas and submicron size soot granules are estimated. An interactive particle-gas model of the stratospheric aerosol is used to compute particle changes due to exhaust emissions, and an accurate radiation transport model is used to compute the attendant surface temperature changes. It is shown that a fleet of several hundred supersonic aircraft, operating daily at 20 km, could produce about a 20% increase in the concentration of large particles in the stratosphere. Aerosol increases of this magnitude would reduce the global surface temperature by less than 0.01 K.

Toon, O. B.↗
NASA NTRS1980

Stratospheric aerosol modification by supersonic transport and space shuttle operations - Climate implications

The potential effects on stratospheric aerosols of supersonic transport emissions of sulfur dioxide gas and submicron soot granules, and space shuttle rocket emissions of aluminum oxide particulates are estimated. An interactive particle-gas model of the stratospheric aerosol layer is used to calculate changes due to exhaust emissions, and an accurate radiation transport model is employed to compute the effect of aerosol changes on the earth's average surface temperature. It is concluded that the release of large numbers of small particles (soot or aluminum oxide) into the stratosphere should not lead to a corresponding significant increase in the concentration of large, optically active aerosols, but that the increase in large particles is severely limited by the total mass of sulfate available to make large particles in situ, and by the rapid loss of small seed particles via coagulation. We find that a fleet of several hundred advanced supersonic aircraft operating daily at 20 km, or the launch of one space shuttle rocket per week, could produce roughly a 20% increase in the large-particle concentration of the stratosphere. We find, in addition, that aerosol increases of this magnitude would reduce the global surface temperature by less than 0.01 K.

Turco, R. P.↗
NASA NTRS1980

The stratospheric sulfate aerosol layer - Processes, models, observations, and simulations

After briefly reviewing the observational data on the stratospheric sulfate aerosol layer, the chemical and physical processes that are likely to fix the properties of the layer are discussed. We present appropriate continuity equations for aerosol particles, and show how to solve the equations on a digital computer. Simulations of the unperturbed aerosol layer by various published models are discussed and the sensitivity of layer characteristics to variations in several aerosol model parameters is studied. We discuss model applications to anthropogenic pollution problems and demonstrate that moderate levels of aerospace activity (supersonic transport and Space Shuttle operations) will probably have only a negligible effect on global climate. Finally, we evaluate the possible climatic effect of a ten-fold increase in the atmospheric abundance of carbonyl sulfide.

Whitten, R. C.↗
NASA NTRS1980

The influence of solar UV variations on climate

The effects on the terrestrial ozone abundance and temperature (and hence on the earth's climate) of periodic variations in the solar spectrum are investigated. Temporal variations of the solar UV spectrum are modeled in accordance with the measurements of Heath and Thekaekara (1977), and the spectrum at wavelengths greater than 2900 A is altered uniformly by small amounts so that the total luminosity remains constant with time. One-dimensional photochemical-radiative-convective models are used to predict the response of the earth's surface to the solar spectral changes. Results show that the data interpreted by Heath and Thekaekara to indicate that the solar UV flux varies by a factor of 2.5 at 1750 A from solar minimum to solar maximum are inconsistent with the historical records of ozone abundance. It is concluded, however, that if the amplitude of solar UV variations increases with increasing period, and if the spectral characteristics variations are similar to the well established solar UV variations over a solar rotation period, these variations could have a significant impact on the earth's climate and the biosphere.

Borucki, W. J.↗