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NASA NTRS1977

The NASA Ames Research Center one- and two-dimensional stratospheric models. Part 1: The one-dimensional model

A one-dimensional model of stratospheric trace constituents is described in detail. Specifically, the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations representing the chemical kinetic terms, and an appropriate method for simulating the diurnal variations of the species concentrations, are discussed. A specialized treatment of atmospheric photodissociation rates is outlined in the text. The choice of a vertical eddy diffusivity profile and its success in predicting the vertical tracer distributions (carbon 14, methane, and nitrous oxide) are also discussed.

Turco, R. P.↗

NASA NTRS1976

Comparison of stratospheric ozone destruction by fluorocarbons 11, 12, 21, and 22

Measured photoabsorption cross sections for fluorocarbons (FC) 11, 12, 21, and 22 are presented for the wavelength region from 1740 A to about 2200 A. Solar radiation in this region dissociates these molecules in the stratosphere releasing atomic chlorine which participates in catalytic reactions that destroy ozone. Photolysis by solar UV is the only known loss mechanism for FC11 and FC12. However, FC21, and FC22 also react with OH in the troposphere reducing the amount of ground level releases which reach the stratosphere. Calculations comparing the steady state stratospheric C1X due to equal release rates of fluorocarbons 11, 12, 21, and 22 are presented using a range of OH profiles and eddy diffusion coefficients. These calculations indicate approximately a factor of 20 to 450 less C1X in the stratosphere for FC21 and a factor of 40 to 130 for FC22, compared to an equal release rate of FC11 and FC12.

Robbins, D. E.↗

NASA NTRS1976

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Hoffert, M. I.↗

NASA NTRS1976

Composition and structure of the Martian upper atmosphere - Analysis of results from Viking

Densities for carbon dioxide measured by the upper-atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the Martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold, with average temperatures for both Viking 1 and Viking 2 of less than 200 K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.

Mcelroy, M. B.↗

NASA NTRS1976

Particles, environments, and possible ecologies in the Jovian atmosphere

The possible existence of indigenous Jovian organisms is investigated by characterizing the relevant physical environment of Jupiter, discussing the chromophores responsible for the observed coloration of the planet, and analyzing some permissible ecological niches of hypothetical organisms. Values of the eddy diffusion coefficent are estimated separately for the convective troposphere and the more stable mesosphere, and equilibrium condensation is studied for compounds containing Na, Cl, or both. The photoproduction of chromophores and nonequilibrium organic molecules is analyzed, and the motion of hypothetical organisms is examined along with the diffusion of metabolites and the consequent growth of organisms. Four kinds of organisms are considered: primary photosynthetic autotrophs ('sinkers'), larger autotrophs or heterotrophs that actively maintain their pressure level ('floaters'), organisms that seek out others ('hunters'), and organisms that live at almost pyrolytic depths ('scavengers'). It is concluded that ecological niches for sinkers, floaters, and hunters appear to exist in the Jovian atmosphere.

Sagan, C.↗

NASA NTRS1977

The clouds of Venus. II - An investigation of the influence of coagulation on the observed droplet size distribution

An approximate numerical technique is used to investigate the influence of coagulation, sedimentation and turbulent motions on the observed droplet size distribution in the upper layers of the Venus clouds. If the cloud mass mixing ratio is less than 0.000001 at 250 K or the eddy diffusivity throughout the cloud is greater than 1,000,000 sq cm per sec, then coagulation is unimportant. In this case, the observed droplet size distribution is the initial size distribution produced by the condensation of the droplets. It is found that all cloud models with droplet formation near the cloud top (e.g., a photochemical model) must produce the observed droplet size distribution by condensation without subsequent modification by coagulation. However, neither meteoritic or surface dust can supply sufficient nucleating particles to account for the observed droplet number density. If the cloud droplets are formed near the cloud bottom, the observed droplet size distribution can be produced solely by the interaction of coagulation and dynamics; all information about the initial size distribution is lost. If droplet formation occurs near the cloud bottom, the lower atmosphere of Venus is oxidizing rather than reducing.

Rossow, W. B.↗

NASA NTRS1977

A dynamical model of upper-atmospheric helium

This numerical study of the global distribution of helium in the terrestrial thermosphere is based on the extension of a three-dimensional single-fluid numerical model of the thermosphere previously developed by the authors to treat the dynamics of a minor gas imbedded in a background gas made up of N2, O2, and O. The Cira (1972) model of the upper atmosphere, based on satellite drag data, is used to specify the background gas density and temperature as functions of altitude, latitude, and local time for a given day of the year. Specific emphasis is placed on a study of the helium distribution at solstice, i.e., the 'winter helium bulge'. Effects of solar activity, eddy diffusion, and exospheric transport on the global distribution of helium are investigated. The model reproduces the general features of the winter helium bulge, including the variation of its amplitude with solar activity, as determined by comparison of data from several recent satellite-borne mass spectrometers.

Straus, J. M.↗

NASA NTRS1977

Particle size distributions and the vertical distribution of suspended matter in the upwelling region off Oregon

Various methods of presenting and mathematically describing particle size distribution are explained and evaluated. The hyperbolic distribution is found to be the most practical but the more complex characteristic vector analysis is the most sensitive to changes in the shape of the particle size distributions. A method for determining onshore-offshore flow patterns from the distribution of particulates was presented. A numerical model of the vertical structure of two size classes of particles was developed. The results show a close similarity to the observed distributions but overestimate the particle concentration by forty percent. This was attributed to ignoring grazing by zooplankton. Sensivity analyses showed the size preference was most responsive to the maximum specific growth rates and nutrient half saturation constants. The verical structure was highly dependent on the eddy diffusivity followed closely by the growth terms.

Kitchen, J. C.↗

NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO was determined by the flash-photolysis resonance fluorescence method to be 7.5 plus or minus 0.9 (2 sigma) times 10 to the minus 11th power cu cm/molecule sec at 298 K and to have a negligible temperature dependence. This rate which is more than 2000 times faster than the rate of Cl + CH4 indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratosphere ozone than previously believed. Ambient stratospheric ozone will depend less on the ambient chlorine amount and the predicted response to chlorine perturbations will be lessened. One-dimensional eddy-diffusion photochemical model calculations indicate a factor of 1.1 less sensitivity to chlorine than recently reported. For a steady-state CFM release at 1975 rates (750,000 tons/year) the eventual ozone depletion is now calculated to be 14%.

Stief, L. J.↗

NASA NTRS1978

Global circulation and distribution of hydrogen in thermosphere of Venus

The global density distribution of atomic H in the upper atmosphere of Venus is determined in terms of a global circulation model. It is shown that H produced on the dayside is efficiently advected to the nightside by the major gas CO2 where it is then convected to lower altitudes and recombines. A maximum night/day H density ratio of about 5 is derived, in which case exospheric return flow from night to day strongly limits the nightside density enhancement. A previously postulated constraint connecting the eddy diffusion coefficient with the escape flux of H in one dimensional models is no longer required when global circulation of H is considered.

Hartle, R. E.↗

NASA NTRS1978

Evaporation of ice in planetary atmospheres: Ice-covered rivers on Mars

The evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. The thickness of the ice is governed principally by the solar flux which penetrates the ice layer and then is conducted back to the surface. Evaporation from the surface is governed by wind and free convection. In the absence of wind, eddy diffusion is caused by the lower density of water vapor in comparison to the density of the Martian atmosphere. For mean martian insolations, the evaporation rate above the ice is approximately 10 to the minus 8th power gm/sq cm/s. Evaporation rates are calculated for a wide range of frictional velocities, atmospheric pressures, and insolations and it seems clear that at least some subset of observed Martian channels may have formed as ice-chocked rivers. Typical equilibrium thicknesses of such ice covers are approximately 10m to 30 m; typical surface temperatures are 210 to 235 K.

Wallace, D.↗

NASA NTRS1978

The sensitivity of a model of the ambient stratosphere to empirical inputs

The usefulness of a general application of sensitivity studies to the modeling of the ambient stratosphere using the GSFC steady-state photochemistry model is examined. The comparison of theoretical model results with field measurements of trace species is used to assess the applicability of the model to the stratosphere, to help determine the eddy diffusion profile, and to validate mechanisms within the photochemistry of the model. Specific examples of each are discussed and the results of a comprehensive sensitivity study used to elucidate certain points about the comparison are analyzed.

Butler, D. M.↗

NASA NTRS1979

A coupled radiative-convective-photochemical model of the stratosphere

A one-dimensional atmospheric model is described. The neutral photochemical processes of the troposphere and stratosphere are presented by a reaction set of 87 kinetic processes and 28 photolytic reactions, with vertical transport being taken into account by an eddy diffusion parameter. The vertical temperature profiles are coupled with the chemical calculations by means of a radiative-convective code. The model has the capability of including effects of multiple scattering and diurnal variations in species concentrations. The numerical solution methodology is described in detail, and current input data are given along with results obtained in a sample calculation.

Boughner, R. E.↗

NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO has been determined by the flash-photolysis-resonance fluorescence method to be + or - 0.9 (2 sigma) x 10 to the -11th power cu cm/molecule per sec at 298 K and to have a negligible temperature dependence. This rate, which at stratospheric temperatures is more than 2000 times faster than the rate of Cl + CH4 and more than a factor of 2 faster than Cl + HO2, indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) and HO2 for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratospheric ozone than previously believed. One-dimensional eddy-diffusion photochemical model calculations indicate that the eventual ozone depletion for a steady-state chlorfluoromethane release at 1975 rates (750,000 tons/year) will be lowered from 20% to 18.5% by the inclusion of this reaction.

Stief, L. J.↗

NASA NTRS1978

Non-thermal hydrogen in the Venus exosphere - The ionospheric source and the hydrogen budget

A nonthermal, or 'hot', Venus corona of H atoms has been observed by Mariners 5 and 10 and Venera 9. Of the sources investigated, reaction of H2 with ionospheric O(+) is still the strongest. It can explain the smaller densities but falls somewhat short of the largest (from Mariner 5). The subsequent recombination of OH(+), supplemented by solar-wind processes, may give an escape flux of 10 million atoms per sq cm/s. The low density of thermal H atoms on the day side has previously been attributed to either a large eddy diffusion coefficient or an escape flux tenfold greater than this. An alternative mechanism, suggested by Hartle and Mayr (1977) is supported: the hydrogen is swept to the night side by strong thermospheric winds. This process is analogous to the 'Johnson pump' for the terrestrial winter helium bulge. Large nightside bulges of H and H2 are predicted; the night/day density ratio is estimated to be as large as 100 for each.

Kumar, S.↗

NASA NTRS1979

The Galilean satellites as a source of CO in the Jovian upper atmosphere

Material from the Galilean satellites of Jupiter ejected by energetic particles in the Jovian magnetosphere may provide large sources of oxygen to the parent planet. Formation of a CO molecule is the ultimate fate of an oxygen atom in the upper Jovian atmosphere. This high-altitude source of CO supports Beer and Taylor's (1978) observations and analysis, provided that the globally averaged O atom input flux is about 10 million per sq cm/sec and the eddy diffusion coefficient at the tropopause is around 1000 sq cm/sec. Implications for the possible presence of other atoms and molecules derived from the satellites are discussed.

Strobel, D. F.↗

NASA NTRS1978

Turbulent convection within rapidly rotating superadiabatic fluids with horizontal temperature gradients

A model is developed for small scale thermally driven turbulent convection in rapidly rotating systems. The Boussinesq equations of adiabatic and inviscid flow are perturbed about a basic state which is superadiabatic and which contains a horizontal temperature gradient balanced by a geostrophic wind. The growth rates and length scales of the most unstable modes are determined. It is found that these modes are either zonally or latitudinally symmetric, depending on the latitude and the horizontal temperature gradient. The transports of heat and momentum by the modes are computed. The linear amplitudes are assumed to be limited by shear instability. The model predicts a latitude dependent eddy diffusivity. The applicability of the model to astrophysical and planetary bodies is briefly discussed.

Flasar, F. M.↗

NASA NTRS1979

An interpretation of the Voyager measurement of Jovian electron density profiles

Electron-density profiles measured for the daytime and nighttime Jovian ionosphere by the Voyager 1 radio-science experiment are analyzed. It is found that the measured profiles can be reproduced by using a model appropriate for an exospheric temperature of 1300 K with temperature varying above the homopause and with an eddy diffusion coefficient of 100,000 to 300,000 sq cm/s at the homopause. An overall rate constant of 4.3 x 10 to the -16th cu cm/s is estimated for the reaction H(+) + H2 (v-prime at least 4) yields H2(+) + H.

Atreya, S. K.↗