Engineering topics

Hansen, J. E.

Publications and source records attributed to Hansen, J. E..

At least 19 records

NASA NTRS1992

Climate forcing by anthropogenic aerosols

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol, in particular, has imposed a major perturbation to this forcing. Both the direct scattering of short-wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

Charlson, R. J.↗

NASA NTRS1986

Atmospheric science on the Galileo mission

The atmospheric science goals of the Galileo mission, and instruments of the probe and orbiter are described. The current data available, and the goals of the Galileo mission concerning the chemical composition of the Jovian atmosphere; the thermal structure of the atmosphere; the nature of cloud particles and cloud layering; the radiative energy balance; atmospheric dynamics; and the upper atmosphere are discussed. The objectives and operations of the atmospheric structure instrument, neutral mass spectrometer, helium abundance interferometer, nephelometer, net flux radiometer, lightning and radio emission detector, solid state imaging system, NIR mapping spectrometer, photopolarimeter radiometer, and UV spectrometer are examined.

Hunten, D. M.↗

NASA NTRS1985

Trace gas effects on climate

The two primary objectives are to describe the new scientific challenges posed by the trace gas-climate problem and to summarize current strategies, and to make an assessment of the trace gas effects on troposphere-stratosphere temperature trends. Numerous reports on CO2-climate problems are examined with respect to climate modeling issues. The role of the oceans in governing the transient climate response to time varying CO2 concentrations is discussed.

Ramanathan, V.↗

NASA NTRS1983

A general circulation model study of atmospheric carbon monoxide

The carbon monoxide cycle is studied by incorporating the known and hypothetical sources and sinks in a tracer model that uses the winds generated by a general circulation model. Photochemical production and loss terms, which depend on OH radical concentrations, are calculated in an interactive fashion. The computed global distribution and seasonal variations of CO are compared with observations to obtain constraints on the distribution and magnitude of the sources and sinks of CO, and on the tropospheric abundance of OH. The simplest model that accounts for available observations requires a low latitude plant source of about 1.3 x 10 to the 15th g/yr, in addition to sources from incomplete combustion of fossil fuels and oxidation of methane. The globally averaged OH concentration calculated in the model is 750,000/cu cm. Models that calculate globally averaged OH concentrations much lower than this nominal value are not consistent with the observed variability of CO. Such models are also inconsistent with measurements of CO isotopic abundances, which imply the existence of plant sources.

Pinto, J. P.↗

NASA NTRS1980

Cloud and haze properties from Pioneer Venus polarimetry

Linear polarization measurements made by the Pioneer Venus orbiter cloud photopolarimeter determined that the low and midlatitude visible clouds mainly contain small H2SO4 droplets with an extensive haze of submicron particles above the cloud group. The polarization of the bright areas poleward of the 55 deg latitude results from the haze which exhibits large spatial and temporal variations. Significant diurnal differences are observed at low latitudes, with more haze close to the morning terminator than near the noon meridian.

Kawabata, K.↗

NASA NTRS1980

Climatic effects of atmospheric aerosols

It is shown quantitatively how radiative climatic forcing by aerosols depends on the physical properties of the aerosols. The special case of atmospheric aerosols produced by volcanic explosions is considered, and evidence is presented which indicates that even the simple climate models available today may be able to capture some of the basic effects of aerosols on global climate. Possible effects of anthropogenic aerosols are briefly examined. It is noted that additional evidence for the significant influence of aerosols on climate may be found in data obtained from recent spacecraft missions to Venus and Mars.

Hansen, J. E.↗

NASA NTRS1979

Cloud images from the Pioneer Venus Orbiter

Ultraviolet images of Venus obtained over a 3-month period show marked evolution of the planetary-scale features in the cloud patterns. The dark horizontal 'Y' feature recurs quasi-periodically at intervals of about 4 days, but has also been absent for periods of several weeks. Bow-shaped features observed in Pioneer Venus images are farther upstream from the subsolar point than those in Mariner 10 images

Travis, L. D.↗

NASA NTRS1979

Jupiter's atmospheric composition and cloud structure deduced from absorption bands in reflected sunlight

The spectrum of sunlight reflected by Jupiter is analyzed by comparing observations of Woodman (1979) with multiple-scattering computations. The analysis yields information on the vertical cloud structure at several latitudes and on the abundance of CH4 and NH3 in the atmosphere of Jupiter. The abundances of CH4 and NH3 suggest that all ices and rocks are overabundant on Jupiter by a factor of 2 or more, providing an important constraint on models for the formation of Jupiter from the primitive solar nebula. The pressure level of the clouds, the gaseous NH3 abundance, the mean temperature profile, and the Clausius-Clapeyron relation suggest that these clouds are predominantly ammonia crystals with the cloud bottom at 600-700 mb. A diffuse distribution of aerosols exists between 150 and 500 mb, and the spectral variation of albedo reflects a changing bulk absorption coefficient of the material composing the aerosols and is diagnostic of the aerosol composition.

Sato, M.↗

NASA NTRS1979

Orbiter cloud photopolarimeter investigation

Polarization measurements by the orbiter cloud photopolarimeter indicate the presence of a planet-wide layer of submicrometer aerosols of substantial visible optical thickness, of the order of 0.05 to 0.01, in the lower stratosphere well above the main visible sulfuric acid cloud layer. Cloud pattern characteristics found by Mariner 10 and by Pioneer are compared. Planetary scale markings, polar region clouds, and cellular features are considered.

Travis, L. D.↗

NASA NTRS1979

Scattering by randomly oriented ellipsoids: Application to aerosol and cloud problems

A program was developed for computing the scattering and absorption by arbitrarily oriented and randomly oriented prolate and oblate spheroids. This permits examination of the effect of particle shape for cases ranging from needles through spheres to platelets. Applications of this capability to aerosol and cloud problems are discussed. Initial results suggest that the effect of nonspherical particle shape on transfer of radiation through aerosol layers and cirrus clouds, as required for many climate studies, can be readily accounted for by defining an appropriate effective spherical particle radius.

Asano, S.↗

NASA NTRS1979

Correlated k-distribution method for radiative transfer in climate models: Application to effect of cirrus clouds on climate

A radiative transfer method appropriate for use in simple climate models and three dimensional global climate models was developed. It is fully interactive with climate changes, such as in the temperature-pressure profile, cloud distribution, and atmospheric composition, and it is accurate throughout the troposphere and stratosphere. The vertical inhomogeneity of the atmosphere is accounted for by assuming a correlation of gaseous k-distributions of different pressures and temperatures. Line-by-line calculations are made to demonstrate that The method is remarkably accurate. The method is then used in a one-dimensional radiative-convective climate model to study the effect of cirrus clouds on surface temperature. It is shown that an increase in cirrus cloud cover can cause a significant warming of the troposphere and the Earth's surface, by the mechanism of an enhanced green-house effect. The dependence of this phenomenon on cloud optical thickness, altitude, and latitude is investigated.

Lacis, A. A.↗

NASA NTRS1978

Mount Agung eruption provides test of global climatic perturbation

The Mount Agung volcanic eruption in 1963 provides the best-documented global radiative perturbation to the earth's atmosphere currently available. Data on stratospheric aerosols produced by this eruption have been used as input to a model for the atmospheric thermal structure. The computed magnitude, sign, and phase lag of the temperature changes in both the stratosphere and the troposphere are in good agreement with observations, providing evidence that the climatic response to a global radiative perturbation is significant as well as support for the use of theoretical models to predict climatic effects.

Hansen, J. E.↗

NASA NTRS1977

The Voyager mission photopolarimeter experiment

A general purpose filter photometer/polarimeter capable of measuring the intensity and linear polarization of scattered light at eight wavelengths in the 2350-7500 A spectral region has been adopted for the Voyager mission photopolarimeter experiment. Objectives of the experiment include determination of the vertical atmospheric aerosol distributions for Jupiter, Saturn and Titan, definition of cloud micro- and macro-structures, and identification of any regular crystalline particles in the clouds. In addition, the density of the satellite atmospheres will be assessed, and the sodium vapor distributions near Io and in the Jovian magnetosphere will be mapped. Particle size and optical depth of Saturn's rings will also be investigated.

Lillie, C. F.↗

NASA NTRS1977

A fast invariant imbedding method for multiple scattering calculations and an application to equivalent widths of CO2 lines on Venus

The invariant imbedding method considered is based on an equation which describes the change in the reflected radiation when an optically thin layer is added to the top of the atmosphere. The equation is used to treat the problem of reflection from a planetary atmosphere as an initial value problem. A fast method is discussed for the solution of the invariant imbedding equation. The speed and accuracy of the new method are illustrated by comparing it with the doubling program published by Hansen and Travis (1974). Computations are performed of the equivalent widths of carbon dioxide absorption lines in solar radiation reflected by Venus for several models of the planetary atmosphere.

Sato, M.↗

NASA NTRS1977

Mt. Agung eruption as a confirmation of the effect of atmospheric radiative perturbations on climate

The effects of the 1963 Mt. Agung (Bali) volcanic eruption are studied with respect to the response of the climate system to global radiative perturbations. Volcanic aerosols, spread globally by stratospheric winds, cause a perturbation characterized by a reasonably well known forcing function. Since the climatic response to a large eruption should be pronounced, these phenomena might provide a means to test the validity of climate models. The Mt. Agung eruption is described, and the atmospheric thermal response is calculated. The magnitude, sign, and time delay of temperature changes computed with a simple one-dimensional climate model for both the stratosphere and troposphere are in agreement with the observed temperature changes.

Hansen, J. E.↗

NASA NTRS1977

Mount Agung eruption provides test of a global climate perturbation

The Mt. Agung volcanic eruption in 1963 is used as a test case to examine the climatic response to a global-scale radiative perturbation of the earth's atmosphere.

Hansen, J. E.↗

NASA NTRS1976

Greenhouse effects due to man-made perturbations of trace gases

Nitrous oxide, methane, ammonia, and a number of other trace constituents of the earth's atmosphere have infrared absorption bands in the spectral range from 7 to 14 microns. Despite their small amounts, these gases can have a significant effect on the thermal structure of the atmosphere by transmitting most of the thermal radiation from the earth's surface to the lower atmosphere. In the present paper, this greenhouse effect is computed for a number of trace gases. The nature and climatic implications of possible changes in the concentrations of N2O, CH4, NH3, and HNO3 are discussed.

Wang, W. C.↗

NASA NTRS1976

A search for short-term meteorological effects of solar variability in an atmospheric circulation model

A set of numerical experiments is carried out to test the short-range sensitivity of the Goddard Institute for Space Studies global atmospheric general-circulation model to changes in solar constant and ozone amount. These experiments consist of forecasts initiated with actual atmospheric data. One set of forecasts is made with a standard version of the model; another set uses the model modified by very different values of the solar constant (two-thirds and three-halves of the standard value) and of the ozone amount (zero and twice the standard amount). Twelve-day integrations with these very large variations show such small effects that the effects of realistic variations would almost certainly be insignificant meteorologically on this time scale.

Somerville, R. C. J.↗