Meteor Observations Research Articles

Observations of overdense Quadrantid radio meteors and the variation of the position of stream maxima with meteor magnitude

Observations of overdense Quadrantid radio meteors and the variation of the position of stream maxima with meteor magnitude

Whaling and Eskimos: Hudson Bay 1860–1915, Ice Core Drilling: Proceedings of a Symposium, University of Nebraska, Lincoln, 28–30 August 1974, Avalanche Handbook, The Periglacial Environment, The Climate of Mt. Wilhelm, The Equatorial Glaciers of New Guinea. Results of the 1971–1973 Australian Universities Expeditions to Irian Jaya: Survey, Glaciology, Meteorology, Biology and Paleoenvironments, International Cloud Atlas, Volume I: Manual on the

Whaling and Eskimos: Hudson Bay 1860–1915, Ice Core Drilling: Proceedings of a Symposium, University of Nebraska, Lincoln, 28–30 August 1974, Avalanche Handbook, The Periglacial Environment, The Climate of Mt. Wilhelm, The Equatorial Glaciers of New Guinea. Results of the 1971–1973 Australian Universities Expeditions to Irian Jaya: Survey, Glaciology, Meteorology, Biology and Paleoenvironments, International Cloud Atlas, Volume I: Manual on the

Trajectories and orbits from the NASA-NMSU Meteor Observatory. II

view Abstract Citations (3) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Trajectories and orbits from the NASA-NMSU Meteor Observatory. II. Harvey, G. A. ; Tedesco, E. F. Abstract Trajectory data and orbital elements for 12 double-station meteors photographed by the NASA-NMSU Meteor Observatory during the winter of 1975-1976 are presented. Three of these are members of the Quadrantid stream. Photoelectric timing of meteors, uncertainties in the derived orbital elements, and monitoring of the night sky with a two-channel photometer are discussed. Publication: The Astronomical Journal Pub Date: June 1977 DOI: 10.1086/112069 Bibcode: 1977AJ.....82..445H Keywords: Descent Trajectories; Meteoroids; Orbital Elements; Astronomical Photometry; Electrophotometry; Night Sky; Astronomy full text sources ADS |

Momentum of meteoroids and its effect on the Earth's atmosphere

Recent studies have attributed certain properties of the Earth's atmosphere to excess orbita angular momentum of impinging meteoroids. A realistic analysis of meteor observations does not support the existence of this excess.

Trajectories and orbits from the NASA-NMSU meteor observatory. I

Reduced trajectory data and orbital elements are reported for 20 double-station meteors photographed at the NASA-NMSU meteor observatory during the winter of 1974/75. The objects photographed include 10 sporadic meteors and 10 members of the Geminid shower. The data for the sporadic meteors indicate that their magnitudes range from 0 to -4, all have eccentricities greater than 0.4, all but three are in direct orbits, and one is probably a member of the Coma Berenicid shower. The elements for the Geminids are obtained using times of appearance chosen by adopting 34.6 km/s as the heliocentric velocity of the shower. The results are compared with previous orbital determinations, and it is concluded that there is no evidence for significant evolution of the Geminid-stream orbit over a period of several decades.

On the initial expansion of meteor trails

The asymptotic solution of the equation governing the number density n( r,t) of evaporated meteoric atons behind a steadily moving meteor is obtained which is suitable to depict the initial expansion of a meteor trail. Some unusual results of meteor observations are elucidated.

Infrasound from a radar-observed meteor

The shock wave produced by the hypersonic entry of a sufficiently large meteoroid into the earth's atmosphere should be detectable at ground level. An array of microbarographs operated at Springhill Meteor Observatory recorded pressure waves on December 14, 1974, believed to be associated with a large meteor detected by the Springhill radars. The time interval between the radar observation and the detection of pressure waves is consistent with an acoustic travel time from the location of the radar echo. Estimates of the meteor mass from the radar echo duration agree with mass estimates calculated from the blast–wave theory of ReVelle. Because no azimuth information was available for the meteor to compare with direction of arrival of the pressure waves, the association is not absolutely certain.

Lunar tide in the upper atmosphere

The conflict between the observed phase of the pressure tide at ground level and that required in the dynamo region to produce the observed magnetic variations led to the conclusion that a phase reversal must occur at some level in the atmosphere. The phase of the pressure tide as indicated by density variations at altitudes between 85 and 110 km, deduced from photographic observations of meteors, is here found to be intermediate between that observed at ground level and that required by dynamo theory. This suggests that the reversal occurs at approximately the level of the photographic meteors.

4.1 Meteors and Interplanetary Dust

AbstractThe contribution of meteor observations to our knowledge of meteoroids and interplanetary dust is reviewed under four headings – flux, mass distribution, physical structure and chemical composition. For lower limits of particle mass ranging from 1 g to 10−5 g the mean cumulative flux into the earth’s atmosphere varies from 2 × 10−15 to 6 × 10−9 particles m−2 s−1 (2Πster)−1, and the mean size distribution of these particles is given by log N = C – 1.3 log M, where N is the cumulative number of particles counted down to a lower mass limit M, and C is a constant. The physical structure of meteoroids in the above range is essentially fragile, with generally low mean bulk densities that tend to increase with decrease in mass. A minor fraction, about 10 or 15 per cent, with orbits lying inside that of Jupiter, have densities several times the average densities, approaching those of the carbonaceous chondrites. The mean chemical composition of meteoroids seems to be similar to the bronzite chondrites for the elements heavier than number 10, but with the probable addition of extra quantities of the light volatiles H, C and O.

Joint microbarograph and radar observations of a meteor

On the night of 13–14 December 1974, joint observations were made at Springhill Meteor Observatory using both meteor radar and a specifically designed array of microbarographs. At about 5 a.m. local time (near the peak of the Geminid meteor shower), a relatively large meteor was recorded on two radars followed about 14 min later by the arrival of infrasonic pressure waves at all four sensors. The signal is not a simple N wave, but contains at least three well-defined cycles (with an overall dominant frequency ∼2 Hz, a peak-to-peak amplitude of ∼6 μ and a total duration of ∼9 sec). Not only is the time delay appropriate (corresponding to an acoustic signal velocity of ∼300 m/sec), but estimates of meteor mass (∼1 kg) made using the radar echo theory of McIntosh and the line source blast wave theory of ReVelle are in good agreement. Unfortunately, due to overcast conditions at the time, photographic data were not available for this event. Additional recordings are currently being made with the Springhill system and a second microbarograph array is being installed on the Canadian Prairies to be operated in conjunction with the camera network of the Meteorite Observation and Recovery Project.

Comment on “superrotation of the upper atmosphere by global deposition of meteoroids”

The hypothesis that superrotation of the Earth's atmosphere results from meteoroid influx is untenable. Meteor observations are not of sufficient precision to substantiate direct rotation when the meteoroid influx is treated macroscopically. Detailed dynamic studies argue against any possible direct rotation.

Television Observations of Faint Meteors - I: MASS DISTRIBUTION AND DIURNAL RATE VARIATION

A low light level television meteor observing system sensitive to stars of magnitude + 8.5 is briefly described. Correction procedures for a non-uniform field of view and the movement of the meteor image are developed. Observations of sporadic meteors with the system yielded a mass distribution index of 2.02 ± 0.04 valid over the absolute magnitude range approximately + 3 to +6. Diurnal rate of occurrence statistics are also presented.

Minor Meteor Showers of October Observed over Waltair during 1962?71

Systematic visual observations of meteors have been made over Waltair Qat. 17� 5� N.) in the month of October during 1962-71. From the data for 1835 meteors collected, after identification of 436 Orionid and 153 Taurid major shower meteors, 56 groups covering 439 meteors in the remainder have been observed to display common radiant points on the daily plotted meteor maps. These 56 groups are tentatively classed as minor meteor showers, after applying some tests of significance. The list is reduced to 20 groups by identifying common radiant coordinates within a divergence of � 10�. Of these 20 groups, 10 occur in at least two different years and on nearby dates and therefore are considered to be well-established minor meteor showers. It is found that a majority of the minor shower radiants lie close to the ecliptic.

The Effect of Wind Shear Gradients on Underdense Radio Meteor Decay Times

It is shown that wind shear gradients in the meteor region can cause a scatter in the decay time of underdense radio meteor echoes. This model agrees well with the experimental observations of forward scatter radio meteors, but in the case of backscatter echoes the wind shear gradient component of the dispersion in the decay times is much smaller than that observed. It is shown that for backscatter echoes the dispersion in decay times is probably almost completely due to cosmic noise.

Micrometeoroids

Much work has been done on measuring the brightness of the zodiacal light and its polarization. Unfortunately the scattering function of a particle depends on its complex index of refraction, its shape, and its size; the brightness and polarization of the zodiacal light therefore depends on the distribution of the sizes, the physical composition, and the spatial distribution of the scatterers. Thus a number of model distributions that explain the same data are derived [Giese, 1963; Powell et al., 19676]. Observations suggest that the particles are concentrated in the ecliptic and that their density falls off far from the sun. Independent observations of radio and photographic meteors and larger objects suggest that the zodiacal light is produced by micrometeoroids with masses of a microgram or smaller, i.e., diameters of 100 μ or smaller.

Laboratory Determination of the Luminous Efficiency of Meteor Constituents

A crossed beam apparatus has been used to measure the emission and ionization cross sections for the prominent spectral features of Na, Ca, Mg, and Fe in collisions with N2 and O2 over the velocity range of 30 to 120 km/s. From the emission and ionization cross sections, the absolute luminous efficiencies in air were determined over the range of meteor velocities. The maximum luminous efficiencies for the brightest features were: greater than 1 percent for the Na D-lines, 0.2 percent for the CaI(2) singlet, 0.06 percent for the MgI(2) and MgI(3) triplets, and O.4 percent for Fe over the visible spectral range. These luminous efficiencies are valid for free molecular flow conditions for velocities above about 30 km/s and are directly applicable to spectroscopic observations of faint meteors. The luminous efficiency of a typical stone will be presented and compared with the efficiencies determined by other investigators. In contrast to previous work, the luminous efficiency found for stone in the present investigation decreases with velocity above about 50 km/s.

Mass Influx Obtained from Low-Light-Level Television Observations of Faint Meteors

Since the advent of low-light-level television (LLLTV) systems, it has been recognized that such devices offer the ability to observe meteors as faint as 10th magnitude which allows the extension of optical meteor data to masses as small as 10-4 gram. The Space Sciences Laboratory at Marshall Space Flight Center has been actively engaged in such observations using image orthicons and intensified SEC vidicons.The results of these observations are presented along with an interpretation in terms of mass-flux. This interpretation includes the development of a relationship between peak luminosity of a meteor and mass, velocity, and zenith angle that was derived from single body meteor theory and compares favorably with results obtained from the Artificial Meteor Program. Also included in the mass-flux interpretation is an analysis of the observation response of a LLLTV system to fixed and moving point sources.

Ablation in Meteors

Photographic and Radar Observations of meteors reveal essential discrepancies from the simplest physical theory of meteors. The simplest theory (Whipple, 1943; Herlofson, 1948; Kascheev et al., 1967) proceeds from the following suppositions: (1) the meteoroid is a dense non-fragmenting body; (2) the sole ablation mechanism is evaporation; and (3) the whole energy transferred to a body by colliding air molecules is spent on evaporation. In addition, the simplest theory of radiowave reflection from meteor trails that does not take into account diffusive and thermodiffusive expansion of a meteor trail and change of the electron line density along the trail is used for the interpretation of the results of radar observations.

Combined Observations of Meteors by Image-Orthicon Television Camera and Multi-Station Radar

Observations from Multiple Sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. The primary purpose of the program was to compare ionization with luminosity. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the following relation for the radar magnitude MR to the panchromatic absolute magnitude Mp, in terms of velocity of the meteor V, was found:

An Unusual Meteor Spectrum

An extraordinary spectrum of a meteor at a velocity of about 18.5±1.0 km s-1 (approximate uncertainty) was observed from the Springhill Meteor Observatory with an image-orthicon camera at 1970 August 10 d2h 48m 518 UT. The radiant of the meteor was at an altitude of about 49°. It was first seen shoioing a yellow-red continuous spectrum alone at a height of 137±8 km (estimated uncertainty) which we ascribe to the first positive group of nitrogen bands. At 1.608 after its initial appearance the meteor had descended to 116±6 km above sea-level when it brightened rapidly from its previous threshold brighness into a uniform continuum. After a further 0.738 at a height of 106±6 km the D-line of neutral sodium appeared and 0.148 later (height 105±5 km) all the other lines of the spectrum also appeared. The continuum remained dominant to the end 0.408 later (height 87±5 km) or 3.878 after initial appearance.Water of hydration and entrained carbon flakes of characteristic dimension about 0.2 micron or less are proposed as constituents of the meteoroid to explain these phenomena.