Leonid Meteor Research Articles

Dynamics of the Leonid Meteoroid Stream: a Numerical Approach

AbstractWe have simulated the evolution of the Leonid stream via numerical integration of 3 million test particles ejected from 55P/Tempel-Tuttle during five perihelion passages of that comet. Using the Whipple ejection velocity formula and a random ejection spread in true anomaly about the parent comet orbit inside 2.3 AU, we have followed the subsequent evolution of Leonid meteoroids differing by over 5 orders of magnitude in mass under the influence of radiation pressure and planetary perturbations. By comparing the model predictions of Leonid activity on a year by year basis with the available observations we have attempted to determine roughly the time of ejection associated with each Leonid storm occurrence and model the observed mass distribution. On the basis of the demonstrated accuracy of the model we make predictions regarding times of peak activity and relative strengths for the Leonid returns for each year during the latter part of the 1990s.

Radar observations of the Leonid meteoroid stream in 1994

Continuous radio wave monitoring of the Leonid meteoroid stream during November 12–21, 1994, has been carried out by using a forward-scatter bistatic radar operating over the Bologna-Lecce baseline in Italy. An enhanced activity starting from November 18 was observed to continue up to November 21. Hourly distribution for different echo duration classes shows that this activity is mainly due to underdense meteors. Nevertheless, there is also a peak due to overdense meteors on November 20. This enhancement in activity of radio meteors, stronger than in visual observations, suggests that the Earth encountered in 1994 the vanguard of P/Tempel-Tuttle comet material.

Activity of the Leonid meteor shower in the years 1944–1953

The activity of the Leonid shower in the years 1944–1953 was derived from visual records obtained at the Skalnate Pleso Observatory, using the zenithal exponent γ = 1.47 in the reduction factor cosγ z R.

Modelling of the new formation structures in the near space

Complex numerical model of young meteor stream formation taking into account reactive deceleration of cometary nucleus and its form change in the process of stream formation is discussed. The model made it possible to predict the existence of fine and superfine structures for young meteor streams, the characteristics of which agree with the observational data on the Draconid and Leonid meteor showers.

Comet Tempel-Tuttle and the Leonid meteors

The distribution of dust surrounding periodic comet Tempel-Tuttle has been mapped by analyzing the associated Leonid meteor shower data over the 902–1969 interval. The majority of dust ejected from the parent comet evolves to a position lagging the comet and outside the comet's orbit. The outgassing and dust ejection required to explain the parent comet's deviation from pure gravitational motion would preferentially place dust in a position leading the comet and inside the comet's orbit. Hence it appears that radiation pressure and planetary perturbations, rather than ejection processes, control the dynamic evolution of the Leonid particles. Significant Leonid meteor showers are possible roughly 2500 days before or after the parent comet reaches perihelion but only if the comet passes closer than 0.025 AU inside or 0.010 AU outside the Earth's orbit. Although the conditions in 1998–1999 are optimum for a significant Leonid meteor shower, the event is not certain because the dust particle distribution near the comet is far from uniform. As a by-product of this study, the orbit of comet Tempel-Tuttle has been redetermined for the 1366–1966 observed interval.

Periodic Comet Tempel-Tuttle and the Leonid Meteor Shower

P/Tempel-Tuttle, the comet associated with the Leonid meteor shower, was observed at only two of its last four passages through perihelion, in 1865–1866 and 1965. We have re-reduced the observations in 1865–1866, and with the help of Belyaev's computer programme for numerical integration have linked the two apparitions.

Ionospheric Si+and SiO+

Summary. Narcisi's observation of Si+ and SiO+ ions in a thin layer at 110 km during a Leonid meteor shower implies an interconversion of these ions. It is proposed that the process involved is an ‘equilibrium’ Si+ + O2 ⇄ SiO+ + O. This process requires an elevated O2 vibrational temperature, from 500° to 1500°K, depending on uncertainties in the SiO+ bond strength. Since SiO+ presumably has a large electron dissociative recombination, the observed Si++SiO+ abundance implies a relatively large atmospheric silicon abundance as compared with other meteor species.

THE LEONIDS BY RADAR—1957 TO 19681

Radar observations of the Leonid meteor shower, made near Ottawa during the years from 1957 to 1968 inclusive, are analyzed and reduced to give comparative flux rates. A strength classification has been made in terms of the ratio of shower rates to background rates. The relative strengths found by radar, showing marked variability from year to year, are confirmed by analysis of available visual observations.There is also great variation in the distribution of particle sizes. The high rates of the 1966 return were accompanied by a relatively high percentage of small particles. In 1965 there was a much higher proportion of large particles, and the high rates of 1961 showed a mass or size distribution intermediate between that of 1966 and of 1965.

Microparticle collection experiments during the 1966 Orionid and Leonid meteor showers

Microparticle collection experiments during 1966 Orionid and Leonid meteor showers accomplished by Luster and ALARR /air launched-air recovered rocket/ instruments

Analyses of particles on surfaces exposed to the 1965 Leonid Meteor Shower by the Luster Sounding Rocket

Particle concentrations and size distribution on Luster sounding rocket surfaces exposed to Leonid meteroid shower, comparing contamination and extraterrestrial origins

Forward transmission from meteor ionization

Results of observations of forward transmission at 39.3 MHz over a 320-mile path are given for a 12-month period from October 1965 to September 1966. Maximum and minimum count rates show no significant seasonal variations although large increases are evident at the expected times of the Geminid and Leonid meteor showers. A large number of long duration reflections are evident which, due to their regularity, are difficult to associate with transient meteor ionizations. They appear to be related to natural and artificial satellites.

44. Investigation of perturbed motion of the leonid meteor stream

The investigation is based on a system of elements, obtained from the best observations made in England during the maximum of the meteor shower 1866. This system represents the most probable orbit of that part of the stream, which passed perihelion during the years 1864–67 and was later given the name of Ortho-Leonids. Seventeen points (meteor groups) have been chosen on this orbit, and differential equations of their motion have been integrated on the electronic computer BESM-2 by Cowell's method of quadratures, taking account of perturbations from eight planets (Venus–Pluto), with a variable step from 0·001 to 40 days and taking account of differences through to the 4th order. The motions of two groups (XI and XII) have been investigated in an interval of 300 years (1700–2000), and the motions of the rest of the groups for a space of 135 years (1866–2000). All the close approaches of these groups to the Earth, Jupiter, Saturn and Uranus have been determined. The results of integration are given in the tables, which clearly represent the evolution of the orbit of every group. It has been found that the basic factors determining the evolution of separate groups, and of the stream as a whole, are the close approaches to the outer planets. The perturbations by these planets, especially by Jupiter and Saturn, determine the conditions for an encounter of the meteor groups with the Earth, and cause a change in the activity of the Leonid shower at different apparitions. Apparitions of the Leonids have been investigated for the last millennium, and in more detail for the last 180 years. It has been stated that the orbit of the Ortho-Leonid stream remained stable over the interval of 1000 years; its stability has been confirmed by calculations during the last 300 years, and the limits of changes of its elements have been computed. The perturbing influence of the Earth on the motion of meteor bodies in its sphere of action has been investigated. It turns out that at exceptionally deep penetrations of meteor bodies into this sphere of action, at a distance of some 1000 km from the Earth, its perturbations can essentially transform the orbit of a meteor body, e.g. reduce its period of revolution by some years, and materially change the eccentricity of the orbit, its inclination, etc. Conditions for an encounter of the stream with the Earth in the period 1898–2000 have been clarified, and forecasts have been made for the times of maximum activity of the shower in the years 1966–68. In 1967 the maximum activity of the Leonids is predicted to occur from November 17, 18h to November 18, 1h UT.

43. Observations of the Leonid meteor shower in November 1966 in the U.S.S.R.

In connection with the expected passage of the Earth through the densest part of the Leonid meteoric stream in November, 1966, the Commission on Comets and Meteors of the Astronomical Council of the U.S.S.R., and the All-Union Astronomical-Geodetic Society, organized visual, photographic and radar observations of the shower at many points in the Soviet Union.

SporadicEas an indicator of wind structure in the lower ionosphere and the influx of meteors

Standard measurements of sporadic E blanketing frequencies (ƒbEs, assumed to indicate peak ion densities) during November 1965 from three temperate latitude stations are examined in the light of current theory that predicts two important properties of this variety of sporadic E: (a) that major events consist predominantly of slowly-recombining monatomic ions, probably of meteoric origin, and (b) that these ions converge and accumulate in thin layers through combined effects of the geomagnetic field and the profile of horizontal winds. Two such levels of convergence seem to be indicated by daytime ƒbEs data. The hypothesis of a meteoric origin for the ions suggests that major events of ƒbEs might correlate with the increased meteoric mass arriving during large showers, as shown by radar meteor data. Some evidence of this correlation is shown during the November 1965 Leonid meteor shower.

Sampling with a luster sounding rocket during a Leonid Meteor Shower

A Luster micrometeoroid sampling payload was successfully launched and recovered during the Leonid meteor shower November 16, 1965, at White Sands Missile Range, New Mexico. The instrument opened at an altitude of 63 km and exposed 2 m2 of sampling surface area. The rocket carried the exposed sampling surfaces to a height of 145 km. The instrument reclosed at 116 km after 206 sec of sampling time and was parachuted to earth after severance from the rocket. An extensive contamination control program using laminar flow clean rooms was applied to all phases of the experiment in an attempt to exclude contaminating particles larger than 0.5 μ. About 3% (264 cm2) of the sampling area has been surveyed with the optical microscope. Every particle larger than 4 μ, which could not be recognized as a known contaminant, has been removed and examined with an electron microprobe X-ray analyzer. On the basis of morphology and chemical composition, each particle has been categorized as to possible origin. Results to date indicate that the number of particles found on this area, which may have an extraterrestrial origin, is much smaller than predictions based on measurements from artificial earth satellites and other sounding rocket collections.

Dusting the upper atmosphere

Two rockets and a balloon were sent up to collect micrometeoroid particles in the upper atmosphere during the Leonid meteor shower at the end of November. The Leonids are a swarm of tiny particles orbiting the sun in an elliptical path that evidently crosses the earth's orbit. Once a year the earth meets the swarm, and a meteor shower lasting several days results. The particles are thought to be cometary debris captured by solar gravitation.

Apparent generation of the difference frequency in ionospheric plasmas illuminated simultaneously at two frequencies

The possibility of the generation of combination or beat frequencies in ionospheric plasmas illuminated simultaneously at two frequencies [Ginzberg, 1961], as well as the allied effect of harmonic generation [Bailey, 1959; also O. G. Villard, private communication, 1960], has been advanced by various investigators. There have been reports [Hakefost, 1936] of experimental verification of the first mentioned phenomenon, although there seems to be some doubt as to the validity of the interpretation of the resulting data in cases in which continuous illuminating transmissions were used [Huxley and Ratcliffe, 1949]. An experiment was conducted during the Leonid meteor shower in 1960 in which two synchronized high-power pulsed HF sources (frequencies approximately 12 and 14 Mc/s) near Washington, D.C. illuminated a common ionospheric volume. Receivers were tuned to the illuminating frequencies, as well as to the sum and difference frequencies. System parameters for the experiment appear in Table 1.

LITHIUM, SODIUM, AND POTASSIUM IN THE TWILIGHT AIRGLOW

A birefringent filter photometer has been used to measure the weaker twilight emissions due to free lithium and potassium atoms, the twilight sodium emission having been monitored simultaneously with an interference wedge photometer. Comparisons of the relative abundances Na/Li and Na/K with those found in meteorites and in sea water suggest that the principal sources are meteorites for the lithium, and the sea for the sodium and potassium.A spectacular seasonal variation of the twilight lithium has been found, showing a correlation with the occurrence of the Leonid meteor shower and with two unusual interplanetary dust showers, one during the interval November 15–18, and the other on February 2. Effects of high-altitude thermonuclear explosions are discussed and it is concluded that these can increase the brightness of twilight lithium emission by 1 to 2 powers of 10.The vertical distributions of all three elements have roughly the same shape. However, the maximum concentration of lithium occurs at 80 km, approximately 11 km below the sodium peak, while the maximum concentration of potassium occurs at about the same height as the sodium peak.The chemistry and ionization of alkalis in the upper atmosphere are considered. It is suggested that the degree of ionization is negligible, and a fast recombination process is discussed. A mechanism for vertical transport of sodium from the lower atmosphere is suggested.

Interplanetary dust particles of micron-size probably associated with the Leonid meteor stream

An interplanetary dust particle event, coincident with the Leonid meteor shower and lasting approximately 70 hours, was recorded by a sensor on the Vanguard III satellite. During this interval the satellite's microphone system registered impacts of approximately 2800 dust particles with momenta exceeding 10(exp -2) dyne-second. The impact rate varied by as much as two orders of magnitude within a few hours. The microphone system was almost omnidirectional, so the radiants of the dust particles cannot be defined. Association of these dust particles with the Leonid meteor stream is suggested by the coincidence in time and by the location of the satellite. Vanguard III traversed five major meteor streams, but the impact rates significantly exceeded the background rate only during this one interval. This is the first case in which a significant increase in the directly measured impact rate of dust particles possibly can be associated with a major meteor stream.

Dust Particles of Micron Size Associated with the Leonid Meteor Stream.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dust Particles of Micron Size Associated with the Leonid Meteor Stream. Alexander, W. M. ; McCracken, C. W. ; Lagow, H. E. Abstract Data from the acoustic system mounted on the satellite, 1959~ (Vanguard III), for registering impacts of interplanetary dust particles on the satellite show a particularly high level of activity during the 16-17 November Leonid meteor shower. Approximately 2800 impacts of particles with momenta greater than 1 X 10-2 dyne sec occurred within a 70-hour interval. The limiting mass sensitivity of the detector for particles of the Leon id stream was 1.3X10-9 g. Two of the sampling intervals contained impact rates of about 7 times the average impact rate for the 70-hr interval. One pass of 6rn+20S duration contained 200+10 impacts, giving a impact rate of 50 times the average rate. In contrast, one sampling interval of 2.3-hour duration contained no impacts. A histogram of the impact rate reveals large variations in the impact rate, implying that there is considerable fine structure in the stream. The presence in the meteor stream of particles of the sizes measured and the fluctuations in the impact rate of such particles are of considerable interest in the study of comet and meteor-stream evolution. Since dynamical perturbations and the Poynting-Robertson effect will tend to rapidly disperse concentrations of small dust particles, the association of such concentrations with a meteor stream suggests a rather recent origin for the observed particles. The possibility of observing dust particles in the micron-size range within particular meteor streams is discussed on the basis of known characteristics of the streams. Publication: The Astronomical Journal Pub Date: March 1961 DOI: 10.1086/108571 Bibcode: 1961AJ.....66S.277A full text sources ADS |