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At least 433 records · Page 24

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NASA NTRS1976

Fireball end heights - A diagnostic for the structure of meteoric material

An earlier analysis of Prairie Network fireball trajectory data failed to discriminate between the varieties of meteoric materials that are thought to be present. The Lost City meteorite event offers another calibration of the fireball data and prompts a reanalysis intended to distinguish between ordinary chondritic meteorites and the more fragile early-type carbonaceous chondrites. The carbonaceous material is expected to ablate more readily and have shorter trajectories or higher end heights. Observational error and natural dispersion in the structures produce severe smoothing effects, and the end-height diagnostic is, in itself, not entirely convincing. However, after making a tentative division of the data, one can discern differences in orbits and beginning heights among the three end-height groups. These are consistent with expectations of the behavior of chondritic stones (group I), weak carbonaceous chondrites (group II), and still more fragile cometary material (group III). It is concluded that if the carbonaceous material occurs in reasonable abundance among the fireballs, it has been properly identified by this analysis.

Ceplecha, Z.↗

NASA NTRS1977

On the origin of extraterrestrial stratospheric particles: Interplanetary dust or meteor ablation debris?

Meteor ablation debris was distinguished from unablated interplanetary dust in a collection of extraterrestrial particles collected in the stratosphere using NASA U-2 aircraft. A 62 g sample of the Murchison (C2) meteorite was artificially ablated to characterize ablation debris for comparison with the stratospheric particles. By using proper experimental conditions, artificial ablation debris can be produced that is similar to natural ablation debris. Analyses of natural fusion crusts, artificial fusion crust, and artificial ablation debris of the Murchison meteorite produced criteria for recognizing debris ablated by a primitive meteoroid. Ninety-five percent of the stratospheric particles can be described as either ablation debris from a primitive meteoroid, or as very primitive interplanetary dust.

Kyte, F. T.↗

NASA NTRS1978

Soviet meteor satellite imagery

Through the cooperative efforts of several agencies, Soviet Meteor satellite visual and infrared (IR) imagery is now being received and processed outside the U.S.S.R. borders. Observations have been made on the data receipt, processing, and subsequent picture quality of the Meteor/APT (Automatic Picture Transmission) system as received by the Cape Canaveral Forecast Facility.

Diesen, B. C., III↗

NASA NTRS1978

Nitric oxide production by Tunguska meteor

The nonequilibrium chemical processes of nitric oxide formation are computed for the wake of the Tunguska meteor of 1908. The wake characteristics are derived by carrying out an optically-thick radiation field analysis for ablation of the meteoroid. The wake flow field is approximated by a one-dimensional, well-stirred reactor model. Known characteristics of the Tunguska event are imposed as constraints, and three controlling parameters - chemical composition, density, and velocity - are varied over a range around the values derived by Korobeinikov et al. (1976) and Petrov and Stulov (1975). The calculation shows that at least 19 million tons of nitric oxide is produced between the altitudes of 10 and 50 km. The anomalous atmospheric phenomena following the event are attributed to the reactions involving nitric oxide thus produced and atmospheric ozone. It is speculated that the nitric oxide produced by the event fertilized the area near the fall, causing the observed rapid plant growth.

Park, C.↗

NASA NTRS1978

Winds from the Atlanta /34 deg N, 84 deg W/ radio meteor wind facility

A brief description of the Georgia Tech radio meteor wind facility is followed by a tabular presentation and discussion of winds measured over Atlanta (34 deg N, 84 deg W) for the first three intervals of the URSI/IAGA Cooperative Tidal Observations Program (CTOP). The pervailing zonal wind measured during August 1974, being easterly, is significantly different from that measured during October 1975 and January 1976, and is not typical of winds measured in August 1975 and August 1976, when westerlies predominated. The complicated tidal picture is detailed, but is not easily summarized.

Roper, R. G.↗

NASA NTRS1978

Urbana Meteor Radar observations during GRMWSP/CTOP periods

Observations with the Urbana Meteor Radar during three GRMWSP/CTOP observational periods are presented. These data were collected at Urbana during the periods 12-13 August 1974, 13-17 October 1975 and 14-23 January 1976. The height-averaged wind is presented for the August period. Determinations of prevailing wind and tidal variability are made during the October period. Tidal determinations and an observed temporary dominance by short period dynamics are presented for the January period. More data supporting our earlier result of a significant correlation between equatorward flow and d-region ionization during winter are shown.

Hess, G. C.↗

NASA NTRS1979

A meteor ablation-cluster ion atmospheric sodium theory

Neutral and ionic forms of sodium form narrow, well-defined layers which peak in the 90-95 km altitude region at midlatitudes. A new theory for the sodium layer is presented, which is found to be in good agreement with existing atmospheric observations as well as available laboratory measurements of rate constants. The layer is believed to result naturally from a meteor ablation source over a chemical sink with vertical transport of Na(+) playing an important role in the layer shape and variation. While the neutral chemistry is believed to consist of chemical equilibrium between Na and NaO, the ion chemistry departs from earlier studies and considers a cluster ion scheme. It is possible that higher-order cluster ions of sodium play a role in the formation of aerosols, through attachment or ion-induced nucleation processes.

Richter, E. S.↗

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

Effect of solar radiation on a swarm of meteoric particles

The theory of the Poynting-Robertson effect is used to study the motion of meteors relative to a parent comet describing an undisturbed elliptical orbit. It is shown that any emitted particle proceeds to move retrogressively away from the comet to a certain maximum angular distance (as seen from the sun) depending on its sigma-s value, and then undergoes relative motion in the opposite forward direction. The time taken to reach this greatest elongation behind the comet is the same for all particles, and after twice this time the particles will have returned to zero angular displacement relative to the comet. For comet Encke the time for the elongation to return to zero is about 6600 y; for Halley it is about 200,000 y; for Temple-Tuttle (1965 IV) it is just over 100,000 y.

Lyttleton, R. A.↗

NASA NTRS1980

Submicron particles in meteor streams

Submicron particles (mass less than 10 to the -15th g) were observed in certain meteor streams by impact detectors on satellite Explorer 46. This unexpected finding leads to conclusions about the nature and origin of the particles and about the importance of nongravitational forces.

Singer, S. F.↗

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 NTRS1980

Meteor Crater: Energy of formation - Implications of centrifuge scaling

Recent work on explosive cratering has demonstrated the utility of performing subscale experiments on a geotechnic centrifuge to develop scaling rules for very large energy events. The present investigation is concerned with an extension of this technique to impact cratering. Experiments have been performed using a projectile gun mounted directly on the centrifuge rotor to launch projectiles into a suitable soil container undergoing centripetal accelerations in excess of 500 G. The pump tube of a two-stage light-gas gun was used to attain impact velocities of approximately 2 km/sec. The results of the experiments indicate that the energy of formation of any large impact crater depends upon the impact velocity. This dependence, shown for the case of Meteor Crater, is consistent with analogous results for the specific energy dependence of explosives and is expected to persist to impact velocities in excess of 25 km/sec.

Schmidt, R. M.↗

NASA NTRS1982

Analysis of photometric spectra of 17 meteors

The initial phase of the photometry which involved 17 meteor spectra consisting of eight Geminid spectra, six Orionid spectra and three Eta Aquarid spectra is discussed. Among these 17 spectra it is found that the Geminid spectra are of the best quality and are used for the identification of the atomic lines and molecular bands that normally appear on video tape spectra. The data from the Geminid records are used for developing calibration techniques in photometry. The Orionid and Eta Aquarid spectra are chosen for early analysis because of the current interest in all physical and chemical data relating to Comet Halley.

Millman, P. M.↗

NASA NTRS1984

Large Scale Winter Time Disturbances in Meteor Winds over Central and Eastern Europe

Daily zonal wind data of the four pre-MAP-winters 1978/79 to 1981/82 obtained over Central Europe and Eastern Europe by the radar meteor method were studied. Available temperature and satellite radiance data of the middle and upper stratosphere were used for comparison, as well as wind data from Canada. The existence or nonexistence of coupling between the observed large scale zonal wind disturbances in the upper mesopause region (90 to 100 km) and corresponding events in the stratosphere are discussed.

Greisiger, K. M.↗

NASA NTRS1984

Interpolation problems in meteor radar analysis, part 7.6A

Meteor echoes come from random points in the observation volume, and are irregularly spaced in time. This precludes the use of fast fourier transformations (FFT) techniques on the raw data to give the spectrum of waves that are present. One way around this obstacle is to restrict our interest to a particular class of waves, and fit a corresponding model to the raw data. It is assumed that there is no horizontal variation across the observation volume for tides, but in the vertical this is certainly not the case. If, in addition, we are interested in other types of waves which may be present and whose periods are unknown, then examining the raw line-of-sight velocities does not tell us how to modify the model, since the line-of-sight direction is not fixed. This is the motivation for interpolation. Interpolation takes a temporal series of line-of-sight velocities, and transforms it to a temporal series of wind velocities for each orthogonal direction. The velocities along a given direction can then be examined readily for any waves in addition to tides.

Tetenbaum, D.↗

NASA NTRS1983

Meteor ablation spherules as chondrule analogs

Meteor ablation spherules are melt products of meteoroids that enter the earth's atmosphere. They are produced by aerodynamic melting, a process that surely produced chondrule-like objects in the early solar system but that apparently did not play a role in forming chondrules found in chondrites. The properties of ablation spherules do, however, provide insight into the chondrule problem because the spheres are chondrule analogs formed by a known process. Although the spheres have strong similarities to meteoritic chondrules, they also differ in significant respects. The differences between the spheres and chondrules suggest that chondrules could not have formed by flash melting of a primitive fine-grained chondritic precursor.

Brownlee, D. E.↗

NASA NTRS1985

Kyoto Meteor Radar Observation in November, 1981 and May, 1982

The Kyoto meteor radar a pulsed Doppler radar and operates at 31.57 MHz ith peak power of 10 kW. An interferometer is adopted for arrival angle measurement. Height resolution is approximately 1 to 3 km depending on both azimuth and elevation angles. Data is analyzed according to an algorithm approved by GROVES. All data in height range 84 to 104 km are separated into five layers, whose altitude width is 4 km. In each layer, least square fitting is performed for ten parameters, which are amplitudes of northward/eastward mean wind and sin/cos component of diurnal/semidiurnal tide. Reliable range for each parameter is also calculated.

Tsuda, T.↗

NASA NTRS1986

Ultraviolet spectroscopy of meteoric debris of comets

It is proposed to carry out slitless spectroscopy at ultraviolet wavelengths from orbit of meteoric debris associated with comets. The Eta Aquarid and Orionid/Halley and the Perseid/1962 862 Swift-Tuttle showers would be principal targets. Low light level, ultraviolet video technique will be used during night side of the orbit in a wide field, earthward viewing mode. Data will be stored in compact video cassette recorders. The experiment may be configured as a GAS package or in the HITCHHIKER mode. The latter would allow flexible pointing capability beyond that offered by shuttle orientation of the GAS package, and doubling of the data record. The 1100 to 3200 A spectral region should show emissions of atomic, ionic, and molecular species of interest on cometary and solar system studies.

Wdowiak, T. J.↗