Engineering topics

Toon, O. B.

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

At least 55 records · Page 3

NASA NTRS1991

Improved Prediction of Atmospheric Heating and Cooling Rates

The demands of accurate predictions of radiative transfer for climate applications are well-documented. While much effort is being devoted to evaluating the accuracy of the GCM radiative transfer schemes, the problem of developing accurate, computationally efficient schemes for climate models still remains. This paper discusses our efforts in developing accurate and fast computational methods for global and regional climate models.

Bergstrom, R. W.↗

NASA NTRS1990

Airborne lidar observations in the wintertime Arctic stratosphere - Ozone

Large-scale distributions of ozone (O3) were measured with an airborne lidar system as part of the 1989 Airborne Arctic Stratospheric Expedition. Measurements of O3 distributions were obtained between January 6 and February 15, 1989, on 15 long-range flights into the polar vortex from the Solar Air Station, Norway. The observed O3 distribution was found to clearly indicate the edge of the polar vortex and to be an effective tracer of dynamical processes in the lower stratosphere. On the last two flights of the expedition, large regions with reduced O3 levels were observed by the lidar inside the polar vortex. Ozone had decreased by as much as 17 percent in the center of these areas, and using the in situ measurements made on the ER-2 aircraft, it was concluded that this decline was due to chemical O3 destruction.

Browell, E. V.↗

NASA NTRS1990

Radiative effects of polar stratospheric clouds

Radiative transfer calculations are performed for polar stratospheric clouds (PSCs) using newly acquired PSC properties and polar atmospheric data. PSC radiative effects depend strongly on upwelling thermal radiation and vary from infrared heating over warm polar surfaces, such as oceans, to cooling over cold surfaces, such as the Antarctic plateau. Heating and cooling rates of nitric acid PSCs are smaller than + or - 0.1 K/day. Rates for optically thicker ice PSCs vary from 1.0 to -0.2 K/day, those for orographically forced ice PSCs even from 3.0 to -0.5 K/day. Frequently observed optically thick cirrus decks near the tropopause provide a very cold radiative surface. These clouds not only act to prevent heating and enhance cooling in ice PSCs to -0.5 K/day and orographic ice PSCs to 2 K/day, but such cirrus cloud decks also cool the entire stratosphere by up to -0.5 K/day over warm surfaces, even in the absence of PSCs.

Kinne, S.↗

NASA NTRS1990

Airborne lidar observations in the wintertime Arctic stratosphere - Polar stratospheric clouds

Polar stratospheric cloud (PSC) distributions in the wintertime Arctic stratosphere and their optical characteristics were measured with a multiwavelength airborne lidar system as part of the 1989 Airborne Arctic Stratospheric Expedition. PSCs were observed on 10 flights between January 6 and February 2, 1989, into the polar vortex. The PSCs were found in the 14-27 km altitude range in regions where the temperatures were less than 195 K. Two types of aerosols with different optical characteristics (Types 1a and 1b) were observed in PSCs thought to be composed of nitric acid trihydrate. Water ice PSCs (Type 2) were observed to have high scattering ratios (greater than 10) and high aerosol depolarizations (greater than 10 percent) at temperatures less than 190 K.

Browell, E. V.↗

NASA NTRS1990

Aerosol nucleation in the winter Arctic and Antarctic stratospheres

The formation rate of sulfuric-acid-water aerosol particles is calculated as a function of altitude for the conditions of the winter Arctic and Antarctic stratospheres. The theoretical results indicate that sulfate particle formation can occur in the polar winter stratosphere. Conditions for new particle formation are increasingly favorable as the altitude increases between 20 and 30 km because of the decrease in surface area of preexisting particles and increasing sulfuric-acid vapor supply. The theoretical predictions are consistent with observations of a high-altitude CN layer over Antarctica in the spring. Available vapor-pressure data indicate that ternary particles composed of sulfuric acid, nitric acid, and water are not thermodynamically stable under winter stratospheric conditions.

Hamill, Patrick↗

NASA NTRS1990

Denitrification of the polar winter stratosphere - Implications of SAM II cloud formation temperatures

The SAM II extinction profiles and the associated temperature profiles are used to determine the amount of denitrification of the winter polar stratospheres. Clear evidence of the denitrification process in the Antarctic data is seen. There are indications in the Arctic data that denitrification mechanisms may be at work there also. At the latitudes observed by the SAM II satellite system, denitrification begins before the formation of extensive ice clouds and may be due to sedimentation of nitric acid particles. However, the possibility of dinitrification by type II PSCs at latitudes not observed by SAM II cannot be excluded.

Hamill, Patrick↗

NASA NTRS1990

Climate and smoke - An appraisal of nuclear winter

A reevaluation is presented of the 'nuclear winter' scenario of Turco et al. (1983). New pertinent data have emerged from laboratory studies, field experiments, and numerical models on the smoke-plume, mesoscale, and global scales. A full-scale nuclear exchange's probable soot injections lead, in three-dimensional climate simulations, to midsummer land temperature decreases averaging 10-20 C in northern midlatitudes, with local cooling of as much as 35 C. Anomalous circulation patterns due to solar heating of the soot could stabilize the upper atmosphere against overturning, thereby prolonging the soot's residence time in the atmosphere. Monsoon disruptions and severe ozone layer depletion are also foreseen.

Turco, R. P.↗

NASA NTRS1989

Antarctic stratospheric ice crystals

Ice crystals were replicated over the Palmer Peninsula at approximately 72 deg S on six occasions during the 1987 Airboirne Antarctic Ozone Experiment. The sampling altitude was between 12.5 and 18.5 km (45-65 thousand ft pressure altitude) with the temperature between 190 and 201 K. The atmosphere was subsaturated with respect to ice in all cases. The collected crystals were predominantly solid and hollow columns. The largest crystals were sampled at lower altitudes where the potential temperature was below 400 K. While the crystals were larger than anticipated, their low concentration results in a total surface area that is less than one tenth of the total aerosol surface area. The large ice crystals may play an important role in the observed stratospheric dehydration processes through sedimentation. Evidence of scavenging of submicron particles further suggests that the ice crystals may be effective in the removal of stratospheric chemicals.

Goodman, J.↗

NASA NTRS1989

Measurements of size and composition of particles in polar stratospheric clouds from infrared solar absorption spectra

Results are presented on polar stratospheric cloud (PSC) observations, based on IR measurements of solar extinction, made by the airborne JPL Mark IV interferometer during the Airborne Antarctic Ozone Expedition in 1987, together with the instrumentation and the theoretical aspects of data analysis. Thirty-three PSC cases were analyzed and categorized into two types, I and II, which were found to occur at different altitudes during September. Type I clouds, seen at altitudes above 15 km, contained particles with radii of about 0.5 micarons and nitric acid concentrations greater than 40 percent, while type II clouds, found usually below 15 km, contained particles with radii of 6 microns and larger, composed of water ice. In addition, particles of larger than the 15-micron-size detection limit were encounterd.

Kinne, S.↗

NASA NTRS1989

The planning and execution of ER-2 and DC-8 aircraft flights over Antarctica, August and September 1987

The significant ozone loss in the lower stratosphere over Antarctica during recent austral springs was studied by instrumented ER-2 and DC-8 aircraft. Data on the homogeneous gas composition, polar stratospheric clouds, and on tracers for dynamic motion are provided. The mission design is described, the aircraft and their payloads are documented, and the flight tracks are specified.

Tuck, A. F.↗

NASA NTRS1989

Condensed nitrate, sulfate, and chloride in Antarctic stratospheric aerosols

The 1987 Airborne Antarctic Ozone Experiment, in which the NO3, Cl, and SO4 contents of stratospheric aerosols were estimated, is discussed. The aerosol size and chemical composition measurements were carried out on samples collected during August 17 to September 4, 1987. The data indicate that condensed nitrate is found below a threshold temperature of 193.6 + or - 3.0 K, which is generally found at latitudes exceeding 64 deg S. A negative correlation exists between condensed nitrate and ozone correlation.

Pueschel, R. F.↗

NASA NTRS1989

Climate evolution on the terrestrial planets

The present comparative evaluation of the long-term evolution of the Venus, earth, and Mars climates suggests that the earth's climate has remained temperate over most of its history despite a secular solar luminosity increase in virtue of a negative-feedback cycle based on atmospheric CO2 levels and climate. The examination of planetary climate histories suggests that an earth-sized planet should be able to maintain liquid water on its surface at orbital distances in the 0.9-1.5 AU range, comparable to the orbit of Mars; this, in turn, implies that there may be many other habitable planets within the Galaxy.

Kasting, J. F.↗

NASA NTRS1989

Studies of radiative effects for polar stratospheric clouds

Data from the Antarctic Ozone Experiment of 1987 are used to model the radiative effects of polar stratospheric clouds. Heating and cooling rates are examined, showing that the heating and/or cooling rates within a polar stratospheric cloud depend on particle size, composition, optical depth of the cloud, solar angle, and temperature profile. The rates for an optically thin Type I cloud are too small to drive vertical motions in the stratosphere, while optically thin Type II clouds cause a stratospheric cooling.

Kinne, S.↗

NASA NTRS1989

Trends in aerosol abundances and distributions

The properties of aerosols that reside in the upper atmosphere are described. Special emphasis is given to the influence these aerosols have on ozone observation systems, mainly through radiative effects, and on ambient ozone concentrations, mainly through chemical effects. It has long been appreciated that stratospheric particles can interfere with the remote sensing of ozone distribution. The mechanism and magnitude of this interference are evaluated. Separate sections deal with the optical properties of upper atmospheric aerosols, long-term trends in stratospheric aerosols, perturbations of the stratospheric aerosol layer by volcanic eruptions, and estimates of the impacts that such particles have on remotely measured ozone concentrations. Another section is devoted to a discussion of the polar stratospheric clouds (PSC's). These unique clouds, recently discovered by satellite observation, are now thought to be intimately connected with the Antarctic ozone hole. Accordingly, interest in PSC's has grown considerably in recent years. This chapter describes what we know about the morphology, physical chemistry, and microphysics of PSC's.

Turco, R. P.↗

NASA NTRS1988

On the growth of nitric and sulfuric acid aerosol particles under stratospheric conditions

A theory for the formation of frozen aerosol particles in the Antarctic stratosphere was developed and applied to the formation of polar stratospheric clouds. The theory suggests that the condensed ice particles are composed primarily of nitric acid and water, with small admixtures of sulfuric and hydrochloric acids in solid solution. The proposed particle formation mechanism is in agreement with the magnitude and seasonal behavior of the optical extinction observed in the winter polar stratosphere.

Hamill, Patrick↗

NASA NTRS1988

A multidimensional model for aerosols - Description of computational analogs

The numerical algorithms used to simulate the advection, diffusion, sedimentation, coagulation, and condensational growth of atmospheric aerosols are described. The model can be used in one, two, or three spatial dimensions. The continuity equation in a generalized horizontal and vertical coordinate system is developed, which allows the model to be quickly adapted to a wide variety of dynamical models of global or regional scale. Algorithms are developed to treat the various physical processes, and the results of simulations are presented, which show the strengths and weaknesses of these algorithms. Although the emphasis is on the modeling of aerosols, the work is also applicable to the simulations of the transport of gases.

Toon, O. B.↗

NASA NTRS1988

Heterogeneous physicochemistry of the winter polar stratosphere

Present chemical theories of the Antarctic ozone hole assume that heterogeneous reactions involving polar stratospheric clouds (PSCs) are the precursor of springtime ozone depletions. However, none of the theories quantify the rates of proposed heterogeneous processed, and none utilize the extensive data base on PSC's. Thus, all of the theories must be considered incomplete until the heterogeneous mechanisms are properly defined. A unified treatment developed of the cloud related processes, both physical and chemical, and the importance of these processes using observation data is calibrated. The rates are compared competitive heterogeneous processes to place reasonable limits on critical mechanisms such as the denitrification and dechlorination of the polar winter stratosphere. Among the subjects addressed here are the physical/chemical properties of PSC's including their relevant microphysical, optical and compositional characteristics, mass transfer rates of gaseous constituents to cloud particles, adsorption, accommodation and sticking coefficients on cloud particles, time constants for condensation, absorption and other microphysical processes, effects of solubility and vapor pressure on cloud composition, the statistics of cloud processing of chemically active condensible species, rate limiting steps in heterogeneous chemical reactions, and the nonlinear dependence of ozone loss on physical and chemical parameters.

Turco, R. P.↗

NASA NTRS1987

Predictions of the electrical conductivity and charging of the aerosols in Titan's atmosphere

Computational results are given for Titan atmosphere aerosol electrical conductivity and charge at altitudes up to 400 km, together with a consideration of ionization from such sources as galactic cosmic rays and electron precipitation from the Saturnian magnetosphere. Predicted conductivity shows the existence of substantial electron concentrations up to the Titan surface. At altitudes of more than 100 km, and aerosol concentrations greater than 10/cu cm, electron/positive ion-recombination is found to be controlled by the recombination of the aerosols' surfaces rather than by the gas-kinetic recombination rate.

Borucki, W. J.↗