Showing papers by "Goddard Space Flight Center published in 1976"
TL;DR: A one-dimensional radiative-convective model for the atmospheric thermal structure is used to compute the change in the surface temperature of the earth for large assumed increases in the trace gas concentrations; doubling the N2O, CH4, and NH3 concentrations is found to cause additive increases inthe surface temperature.
Abstract: Nitrous oxide, methane, ammonia, and a number of other trace constituents in the earth's atmosphere have infrared absorption bands in the spectral region 7 to 14 µm and contribute to the atmospheric greenhouse effect. The concentrations of these trace gases may undergo substantial changes because of man's activities. Extensive use of chemical fertilizers and combustion of fossil fuels may perturb the nitrogen cycle, leading to increases in atmospheric N_2O, and the same perturbing processes may increase the amounts of atmospheric CH_4 and NH_3. We use a one-dimensional radiative-convective model for the atmospheric thermal structure to compute the change in the surface temperature of the earth for large assumed increases in the trace gas concentrations; doubling the N_2O, CH_4, and NH_3 concentrations is found to cause additive increases in the surface temperature of 0.7°, 0.3°, and 0.1°K, respectively. These systematic effects on the earth's radiation budget would have substantial climatic significance. It is therefore important that the abundances of these trace gases be accurately monitored to determine the actual trends of their concentrations.
485 citations
TL;DR: The results of an extensive study of plasma waves in the distant magnetotail on the basis of measurements from the Imp 8 spacecraft are discussed in this article, where three distinctly different types of plasma wave turbulence are detected.
Abstract: The results of an extensive study of plasma waves in the distant magnetotail on the basis of measurements from the Imp 8 spacecraft are discussed. The plasma measurements are compared with plasma and magnetic field measurements described by Frank et al. (1976) to study the relationship of the plasma waves to the various plasma regimes found in the distant magnetotail. Three distinctly different types of plasma wave turbulence in the distant magnetotail are detected. The first, most frequently occurring type of turbulence, consists of broadband electrostatic noise at frequencies between 10 Hz and a few kHz. The second, less frequent type of plasma wave turbulence consists of intense (100 milligamma) bursts of low frequency (10 to 300 Hz) magnetic noise. The third, least frequent type of turbulence consists of electrostatic waves near harmonics of the electron gyrofrequency.
356 citations
TL;DR: In this paper, detailed Monte Carlo calculations of the interaction histories of ultra-high energy cosmic-ray nuclei with intergalactic radiation fields are presented, including multinuclear disintegrations for nuclei up to 56Fe.
Abstract: Results of detailed Monte Carlo calculations of the interaction histories of ultrahigh energy cosmic-ray nuclei with intergalactic radiation fields are presented. Estimates of these fields and empirical determinations of photonuclear cross sections are used, including multinuclear disintegrations for nuclei up to 56Fe. Intergalactic and galactic energy loss rates and nucleon loss rates for nuclei up to 56Fe are also given. Astrophysical implications are discussed in terms of expected features in the cosmic-ray spectrum between quintillion and sextillion eV for the universal and supercluster origin hypotheses. The results of these calculations indicate that ultrahigh energy cosmic rays cannot be universal in origin regardless of whether they are protons or nuclei. Both the supercluster and galactic origin hypotheses, however, are possible regardless of nuclear composition.
299 citations
TL;DR: In this article, the microwave brightness temperature for snow fields was studied assuming that the snow cover consists of closely packed scattering spheres which do not interact coherently, and the Mie scattering theory was used to compute the volume scattering albedo.
Abstract: The microwave brightness temperature for snow fields was studied assuming that the snow cover consists of closely packed scattering spheres which do not interact coherently. The Mie scattering theory was used to compute the volume scattering albedo. It is shown that in the wavelength range from 0.8 to 2.8 cm, most of the micro-radiation emanates from a layer 10 meters or less in thickness. It is concluded that it is possible to determine snow accumulation rates as well as near-surface temperature.
235 citations
TL;DR: In this paper, the evolution of rotating stars is studied well beyond the main-sequence stage and four different cases of redistribution of angular momentum in an evolving star are considered, and a method is developed which allows the evolution to be studied well past the main sequence stage.
Abstract: A method is developed which allows the evolution of rotating stars to be studied well beyond the main-sequence stage. Four different cases of redistribution of angular momentum in an evolving star are considered. Evolutionary sequences for a 7-solar-mass star, rotating according to these different cases, were computed from the zero-age main-sequence to the double-shell-source stage. Each sequence was begun with a (typical) equatorial rotational velocity of 210 km/s. On the main sequence, the effects of rotation are of minor importance. However, as the core contracts during later stages, important effects arise in all physically plausible cases. The outer regions of the cores approach critical velocities and develop unstable angular-velocity distributions. The effects of these instabilities should significantly alter the subsequent evolution.
229 citations
TL;DR: In this paper, the radial dependence of low-energy particle events was studied between 1 and 4.6 A.U. using essentially identical low energy detector systems on IMP 7, Pioneer 10 and Pioneer 11.
Abstract: Co-rotating proton and electron streams are the dominant type of low-energy (0.1-10 MeV/nucleon) particle event observed at 1 A.U. The radial dependence of these events was studied between 1 and 4.6 A.U. using essentially identical low-energy detector systems on IMP 7, Pioneer 10 and Pioneer 11. It was expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead it was found that from event to event the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 3 A.U. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are explored.
183 citations
TL;DR: In this article, the fundamental physical principles essential to an understanding of waveguide gas and liquid lasers, and the current technological state of these devices are discussed, as well as their applications and their current state of the art.
Abstract: The present article reviews the fundamental physical principles essential to an understanding of waveguide gas and liquid lasers, and the current technological state of these devices. At the present time, waveguide laser transitions span the visible through submillimeter regions of the wavelength spectrum. The introduction discusses the many applications of waveguide lasers and the wide variety of laser configurations that are possible. Section 1 summarizes the properties of modes in hollow dielectric waveguides of circular, rectangular, and planar cross section. Section 2 considers various approaches to optical feedback including internal and external mirror Fabry-Perot type resonators, hollow waveguide distributed feedback structures, and ring-resonant configurations. Section 3 discusses those aspects of molecular kinetic and laser theory pertinent to the design and optimization of waveguide gas lasers such as the scaling laws for discharge-excited gas lasers, molecular models useful in maximizing the oscillation bandwidth, the effects of gas flow rate, and the physics of optically-pumped far-infrared lasers. Finally, a review of the waveguide gas and liquid lasers reported to date is given in Section 4.
177 citations
TL;DR: In this paper, a theory of electron-molecule scattering was developed which was a synthesis of close coupling and adiabatic-nuclei theories, and the theory is shown to be a close coupling theory with respect to vibrational degrees of freedom but is a adi-abatic nuclei theory in respect to rotation.
Abstract: A theory of electron-molecule scattering was developed which was a synthesis of close coupling and adiabatic-nuclei theories. The theory is shown to be a close coupling theory with respect to vibrational degrees of freedom but is a adiabatic-nuclei theory with respect to rotation. It can be applied to any number of partial waves required, and the remaining ones can be calculated purely in one or the other approximation. A theoretical criterion based on fixed-nuclei calculations and not on experiment can be given as to which partial waves and energy domains require the various approximations. The theory allows all cross sections (i.e., pure rotational, vibrational, simultaneous vibration-rotation, differential and total) to be calculated. Explicit formulae for all the cross sections are presented.
163 citations
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01 Jan 1976TL;DR: In this paper, the authors examined the distribution of tektite distribution, taking into account the Australasian strewn fields, the Ivory Coast strewn field, the Moldavite Strewn Field, the North American strewnfield, the Libyan desert glass, the Aouelloul crater glass, and amerikanites, concluding that tektites cannot be terrestrial in origin.
Abstract: Questions concerning the tektite distribution are examined, taking into account the Australasian strewn field, the Ivory Coast strewn field, the Moldavite strewn field, the North American strewn field, the Libyan desert glass, the Aouelloul crater glass, and amerikanites. Attention is given to the shapes of tektites, the internal structure of tektites, the physical properties of tektite glass, the chemical composition of tektites, isotopes, fission tracks, cosmic ray tracks, and arguments in favor and against the terrestrial origin of tektites. It is concluded that tektites cannot be terrestrial in origin. They are probably volcanic ejects, of geologically recent epochs, from one or a number of lunar volcanoes.
153 citations
TL;DR: The most prevalent microscale fluctuations appeared to be large-amplitude Alfven waves with small but non-zero fluctuations in the magnetic field intensity as mentioned in this paper, and these waves are present about 40% of the time and are predominantly propagating away from the sun.
Abstract: Analysis of IMP 1 (Explorer 43) plasma and magnetic field fluctuations on a scale of one hour revealed that linearly and circularly polarized Alfven waves are rarely present in the solar wind at 1 AU. The most prevalent microscale fluctuations appeared to be large-amplitude Alfven waves with small but non-zero fluctuations in the magnetic field intensity. These waves are present about 40% of the time and are predominantly propagating away from the sun.
139 citations
TL;DR: Results from the aeroshell-mounted neutral mass spectrometer on Viking I indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO.
Abstract: Results from the aeroshell-mounted neutral mass spectrometer on Viking 1 indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180 plus or minus 20 deg K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241 deg K. The descent data are consistent with the view that CO2 should be the major constituent of the lower Martian atmosphere.
TL;DR: Magnetic field observations made during the third encounter of Mariner 10 with Mercury are discussed along with implications of an intrinsic field for the planetary interior as mentioned in this paper, and it is concluded that an active dynamo is a more likely candidate than fossil magnetization for the origin of the field.
TL;DR: A radiative transfer model with a known mass of dust that is constructed with knowledge of a few values of optical parameters measured from a surface ship is developed to account for the measured radiance values.
Abstract: Landsat 1 measurements of nadir radiance are used to obtain the mass of particulates in a vertical column of dust from the Sahara Desert. A radiative transfer model, constructed with knowledge of a few values of optical parameters measured from a ship, is developed to account for the measured radiance values. Measurement and model accuracies are discussed. It is found that the mass of particulates with smaller than a 10 micron radius in a vertical column is 1.6 g/sq m.
TL;DR: Several methods by which a magnetic field in space can be represented with particular attention to problems of the observed geomagnetic field are reviewed in this paper, and five main classes of representation are described by vector potential, scalar potential, orthogonal vectors, Euler potentials and expanded magnetic field.
Abstract: Several methods by which a magnetic field in space can be represented are reviewed with particular attention to problems of the observed geomagnetic field. Time dependence is assumed to be negligible, and five main classes of representation are described by vector potential, scalar potential, orthogonal vectors, Euler potentials, and expanded magnetic field.
TL;DR: Aircraft observations of the microwave emission from the wind-driven foam-covered Bering Sea substantiate earlier results and show that the combination of surface roughness and white water yields a significant microwave brightness temperature dependence on wind speed over a wide range of microwave wavelengths, with a decreasing dependence for wavelengths above 6 cm as mentioned in this paper.
Abstract: Aircraft observations of the microwave emission from the wind-driven foam-covered Bering Sea substantiate earlier results and show that the combination of surface roughness and white water yields a significant microwave brightness temperature dependence on wind speed over a wide range of microwave wavelengths, with a decreasing dependence for wavelengths above 6 cm. The spectral characteristic of brightness temperature as a function of wind speed is consistent with a foam model in which the bubbles give rise to a cusped surface between the foam and the sea. In the fetch-limited situation the contribution of the wave structure at the surface appears to increase as the foam coverage decreases. Although the data show that the thin streaks are the most important part of the white water signature, there is some evidence for the contribution of whitecaps.
TL;DR: In this article, the authors used a graph for two water vapor levels, as a function of the surface reflectivity, for various sun elevation angles to estimate the surface albedo for the entire solar spectrum.
TL;DR: In this article, the presence of a net current flowing into or away from the ionosphere in a current layer was inferred from the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude.
Abstract: From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.
01 Jan 1976
TL;DR: In this paper, the authors describe the Lunar Ejecta and meteorites (LEAM) experiment of the Apollo 17 flight mission, placed in the Taurus-Littrow area of the moon.
Abstract: The paper describes the Lunar Ejecta and Meteorites (LEAM) experiment of the Apollo 17 flight mission, placed in the Taurus-Littrow area of the moon. The objective of the experiment was to measure impact parameters of cosmic dust on the lunar surface. Preliminary data analysis led to the recognition that the bulk of events recorded by the LEAM experiment are not signatures of hypervelocity cosmic dust particles as expected, but are induced signatures of electrostatically charged and transported lunar fines.
TL;DR: In this article, a plasma strong turbulence, weak coupling theory is applied to the problem of cosmic-ray pitch-angle scattering in magnetostatic turbulence, and a detailed calculation is presented for a model of'slab' turbulence with an exponential correlation function.
Abstract: A plasma strong turbulence, weak coupling, theory is applied to the problem of cosmic-ray pitch-angle scattering in magnetostatic turbulence. The theory used is a rigorous generalization of Weinstock's 'resonance broadening' theory and contains no ad hoc approximations. A detailed calculation is presented for a model of 'slab' turbulence with an exponential correlation function. The results agree well with numerical simulations. The rigidity dependence of the pitch-angle scattering coefficient differs from that found by previous researchers. The differences result from an inadequate treatment of particle trajectories near 90 deg pitch angle in earlier work.
TL;DR: In this article, the abundance of cosmic ray-produced noble gases and Al-26, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages less than 3,000,000 yr.
01 Jun 1976
TL;DR: In this article, the results of thermal and microwave studies of soil moisture are presented, and the relative advantage of each method is discussed, and a comparison of the two methods is made.
Abstract: The results of thermal and microwave studies of soil moisture are presented, and the relative advantage of each method is discussed.
TL;DR: The response of the plasma mantle to the orientation of the interplanetary magnetic field (IMF) has been studied by correlating Heos 2 plasma and Imp 6 magnetic field data as mentioned in this paper.
Abstract: The response of the plasma mantle to the orientation of the interplanetary magnetic field (IMF) has been studied by correlating Heos 2 plasma and Imp 6 magnetic field data. The mantle is nearly always present when the IMF has a southward component and often also when the field has a weak northward component. In addition, the mantle appears increasingly thicker with greater southward components. On the other hand, the mantle is thin or missing (from the region where it is normally found) when the average IMF has a strong northward component. This result supports the idea that polar cap convection plays a dominant role in the formation of the plasma mantle: mantle plasma originates in the magnetosheath, enters the magnetosphere through the day side polar cusps, and is transported across the cusp to the night side by means of a convection electric field whose magnitude is controlled by the orientation of the IMF.
TL;DR: The magnetic field of the magnetosheath is most naturally discussed in terms of its steady state and its fluctuating components Theory of the steady state field is quite well developed and its essential features have been confirmed by observations as mentioned in this paper.
Abstract: The magnetic field of the magnetosheath is most naturally discussed in terms of its steady state and its fluctuating components Theory of the steady state field is quite well developed and its essential features have been confirmed by observations The interplanetary field is convected through the bow shock where its magnitude is increased and its direction changed by the minimal amount necessary to preserve the normal component across the shock Convection within the magnetosheath usually increases the magnitude still further near the subsolar point and further distortes the direction until the field is aligned approximately tangent to the magnetopause Fluctuations of the magnetosheath field are very complex, variable and not well understood Spectral peaks are common features which occur at different frequencies at various times Perturbation vectors of hydromagnetic waves tend to be aligned with the shock and magnetopause surfaces Magnetosheath waves may be generated upstream, within the magnetosheath, at the bow shock, or at the magnetopause, but the relative importance of these sources is not known
TL;DR: In this paper, a flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain absolute rate parameters for the reaction of atomic hydrogen with acetylene.
Abstract: The technique of flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain absolute rate parameters for the reaction of atomic hydrogen with acetylene, i.e., H+C2H2?C2H3* (1); C2H3*+M→C2H3+M (2). The rate constant for the reaction is strongly pressure dependent and was measured over the pressure range 10 to 700 torr. The reaction was also studied as a function of temperature over the range 193 to 400 °K and the high pressure limit of the rate constant at each temperature was used to obtain the Arrhenius expression k1= (9.63±0.60) ×10−12 exp(−2430±30/1.987T) cm3 molecule−1⋅sec−1. The present results are compared with those of previous studies.
TL;DR: In this paper, an analysis of All-Sky Monitor observations of Cir X-1 (3U 1516-56) over the period from October 1975 to April 1976 has revealed a well-defined modulation of the 3-6-keV flux at a period of 16.585(+ or - 0.01) days.
Abstract: Analysis of All-Sky Monitor observations of Cir X-1 (3U 1516-56) over the period from October 1975 to April 1976 has revealed a well-defined modulation of the 3-6-keV flux at a period of 16.585(+ or - 0.01) days. The light-curve is characterized by an abrupt drop in emission occurring on a time scale of no more than about 0.07 day, with epoch JD 2,442,877.181(+ or - 0.07). No clear correspondingly sharp increase in emission is observed during the cycle, so a noneclipse origin for this effect cannot be ruled out.
TL;DR: In this article, the locations of the sources of terrestrial kilometric radiation (TKR) were estimated by examining the two dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere.
Abstract: Observations are presented of lunar occultations of the earth at 250 kHz obtained with the Radio-Astronomy-Explorer-2 satellite which were used to derive two dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250 kHz electron gyro or plasma level (approximately 2 earth radii), many events are observed much farther from the earth (between 5 and 15 earth radii). Dayside emission apparently in the region of the polar cusp and the magnetosheath and night emission associated with regions of the magnetotail are examined. The nightside emission is suggestive of a mechanism involving plasma sheet electron precipitation in the pre-midnight sector.
TL;DR: A general survey of solar radiation measurement, the techniques and instrumentation is presented in this article, where the importance of determining the total and spectral irradiance of the Sun is examined in the context of the energy crisis and utilization of solar energy.
TL;DR: In this paper, an analysis of pulsar average waveforms at radio frequencies from 40 MHz to 15 GHz is presented based on the hypothesis that the observer sees one cut of a hollow-cone beam pattern and that stationary properties of the emission vary over the cone.
Abstract: An analysis of pulsar average waveforms at radio frequencies from 40 MHz to 15 GHz is presented. The analysis is based on the hypothesis that the observer sees one cut of a hollow-cone beam pattern and that stationary properties of the emission vary over the cone. The distributions of apparent cone widths for different observed forms of the average pulse profiles (single, double/unresolved, double/resolved, triple and multiple) are in modest agreement with a model of a circular hollow-cone beam with random observer-spin axis orientation, a random cone axis-spin axis alignment, and a small range of physical hollow-cone parameters for all objects.
01 Apr 1976
TL;DR: In this paper, basic mathematical formulations depict coordinate and time systems, perturbation models, orbital estimation techniques, observation models, and numerical integration methods, as well as numerical integration method.
Abstract: Basic mathematical formulations depict coordinate and time systems, perturbation models, orbital estimation techniques, observation models, and numerical integration methods.
TL;DR: In this paper, published data on the interstellar scintillations of three pulsars were analyzed using a theory based on the Markov approximation for strong scintillation, and the data were found to be consistent with either a Gaussian or Kolmogorov-like power-law irregularity spectrum for the interstellar material.
Abstract: Published data on the interstellar scintillations of three pulsars are analyzed using a theory based on the Markov approximation for strong scintillations. The data are found to be consistent with either a Gaussian or Kolmogorov-like power-law irregularity spectrum for the interstellar material. For two of the pulsars, application of the Kolmogorov power law suggests the presence of regions of larger than normal electron density between us and the pulsar. The parameters of the deduced power-law spectrum are considered with independent measures of the large-scale structures of the gas and indicate the possibility of a broadly turbulent interstellar medium with a Kolmogorov-like spectrum.