Leonid Meteor Research Articles

Observations of persistent Leonid meteor trails: 1. Advection of the “Diamond Ring”

From a single image of a persistent trail left by a −1.5 magnitude Leonid meteor on November 17, 1998, the relative winds between 92.5 and 98 km altitude are derived, where the altitudes are determined by a sodium lidar. These are converted to true winds 82 sec after the appearance of the meteor by fixing the winds at 98 km to match the results of following the trail with the lidar for twelve minutes. The image and winds reveal a fine example of the effects of a gravity wave having a vertical wavelenth of 5.50 ± 0.02 km, a horizontal wavelength of 2650 ± 60 km, an intrinsic period of 19.5 ± 0.4 hours, and an observed period of 8.6 ± 0.1 hours. Effects of the gravity wave are still present in the wind field 70 min later.

Observations of persistent Leonid meteor trails: 2. Photometry and numerical modeling

During the 1998 Leonid meteor shower, multi‐instrument observations of persistent meteor trains were made from the Starfire Optical Range on Kirtland Air Force Base, New Mexico, and from a secondary site in nearby Placitas, New Mexico. The University of Illinois Na resonance lidar measured the Na density and temperature in the trains, while various cameras captured images and videos of the trains, some of which were observed to persist for more than 30 min. The Na density measurements allow the contribution of Na airglow to the observed train luminescence to be quantified for the first time. To do this, persistent train luminescence is numerically modeled. Cylindrical symmetry is assumed, and observed values of the Na density, temperature, and diffusivity are used. It is found that the expected Na luminosity is consistent with narrowband CCD all‐sky camera observations, but that these emissions can contribute only a small fraction of the total light observed in a 0.5–1 μ bandwidth. Other potential luminosity sources are examined, in particular, light resulting from the possible excitation of monoxides of meteoric metals (particularly FeO) and O2(b1∑g+) during reactions between atmospheric oxygen species and meteoric metals. It is found that the total luminosity of these combined processes falls somewhat short of explaining the observed brightness, and thus additional luminosity sources still are needed. In addition, the brightness distribution, the so‐called hollow cylinder effect, remains unexplained.

The 1999 Quadrantids and the lunar Na atmosphere

Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical–physical properties of the Leonid and Quadrantid streams may be responsible for the difference.

High resolution Leonid meteor light curves: implied meteoroid structure

We observed the recent Leonid meteor storm with CCD in 1998 and 1999. The high spatial resolution light curves extracted from the two-dimensional images of the bright Leonid meteors clearly show in-flight fragmentation of these meteors, which is the first direct evidence supporting the dustball meteor model.

A micrometeor component of the 1998 Leonid shower

Most astronomers expected a significant meteor shower associated with the Leonid meteoroid stream to appear in 1998 and 1999. An enhanced shower was widely observed in both years, and details can be found in many published articles. In 1998, one remarkable feature was the appearance of a strong component, rich in bright meteors, which appeared about 16 h before the expected maximum of the main shower, but another observed feature was an abnormal peak in the ionosphere characteristic value f(b)E(s) which was detected about 18 h after the main shower. A very high value of f(b)E(s) persisted for over an hour. The likely explanation is that the ionosphere was bombarded by an additional swarm of meteoroids, much smaller than those that produce a visible trail or an ionization trail that can be picked up by radio detectors. The different dynamical behaviours between small and large meteoroids are investigated and, in consequence, an explanation for the observed phenomena is offered and 1933 is suggested as being the likely ejection time.

Impact of a major meteor storm on Earth's ionosphere: A modeling study

A comprehensive model of the effect of a major meteor storm on Earth's ionosphere is presented. The model includes meteor stream mass distributions based on visual magnitude observations, a differential ablation model of major meteoric metals, Fe and Mg, and state‐of‐the‐art modeling of the chemistry and transport of meteoric metal atoms and ions subsequent to deposition. Particular attention is paid to the possibility of direct ionic deposition of metallic species. The model is validated by calculating the effect of annual meteor showers on the background metal atom and ion abundances. A metallic ion density increase of up to 1 order of magnitude is observed, in agreement with in situ measurements during showers. The model is exercised for a hypothetical Leonid meteor storm of the magnitude reported in 1966. The model predicts the formation of a layer of metal ions in the ionospheric E region that reaches peak densities of around 1 × 105 cm−3, corresponding to a 2 order of magnitude increase of the quiescent nighttime E region density. Although sporadic E layers reaching or exceeding this density are relatively common, the effect is different in that it persists on the order of days and would be observed over nearly one‐half the globe. The model predictions are consistent with the available 1966 Leonid storm data. In particular, the observation of enhanced, predawn sporadic E activity points to efficient collisional ionization of meteoric metals, as assumed in the model.

The Third Peak of the 1998 Leonid Meteor Shower

The Leonid meteor shower in November 1998 was observed widely by astronomers. The first peak, rich in bright meteors, appeared about 16 hours before the predicted maximum of the main shower. The main shower was also observed by both optical and radio methods during 19:00-21:00 UT on Nov. 17, and the radio peak was over 2500 h(-1). About 18 hours after the main shower, an abnormal phenomenon in the ionosphere was detected by two separate ionosphere observing stations. And the very high abnormal phenomenon maintained over one flour. The phenomenon showed that the ionosphere was injected with a large amount of small dust particles that could not be observed in optical and radio. The observational results show that the Leonid meteor shower in 1998 had three peaks.

Radio Signatures of November 1998 Leonid Meteor on Transionospheric VHF Satellite Signal

This letter presents, to our knowledge for the first time, two cases of scintillations of the 244 MHz satellite beacon signal recorded from the geostationary satellite FLEETSATCOM (FSC) (Long: 73°E) at the Haringhata Field Station (HFS) (Lat: 22.97°N Long: 88.50°E Dip: 32°N) of the University of Calcutta on the night of November 16/17, 1998, which corresponds to the peak period of the Leonid meteor shower in terms of its rate and visual magnitude. Scintillations produced by the sporadic-E layer (E s) generated by meteoric ionization are transient and quasi-periodic in nature. This type of scintillations have much shorter durations (∼30–100 s) than those normally observed at night in the equatorial latitudes (∼5 min to couple of hours). It is characterized by a primary deep fade out in field strength, associated with regular ringing patterns before and after it. Generation of quasi-periodic scintillations is believed to be due to a small-scale (scale size ∼100–1000 m) density enhancement or blob which acts as a radio lens in the path of the transionospheric signal. Assuming one-dimensional density irregularities, the peak phase deviation introduced in the radio wave passing through is estimated. The observed scintillation patterns have been simulated considering a series of isolated ionospheric irregularities of different strengths and scale sizes. Critical frequency of the E s layer (f 0E s) measured by the Ahmedabad ionosonde (Lat: 23.03 0N Long: 72.40 0E Dip: 34°N) for the same night shows two isolated spikes which may be due to a sudden increase in plasma density caused by meteoric ionization. In addition, the meteor visual magnitude and cumulative mean flux have been calculated using the meteor intensity data available on the Internet.

Orbital Properties of the Arecibo Micrometeoroids at Earth Interception

Using the Arecibo Observatory (AO) 430-MHz Radar we have developed a Doppler technique to measure very precise micrometeor instantaneous velocities directly from the meteor head echo. In addition, a large number of the observed meteoroids show deceleration. With the velocity, the deceleration, and the assumptions of a spherical shape and a mean micrometeoroid mass density, we have obtained estimates of in-atmosphere particle sizes. The size estimate, the MSIS model atmosphere, and the measured deceleration are used to obtain the meteor extra-atmospheric speeds, assuming these particles undergo little mass-loss prior to and during the time we detect them (Janches et al. 2000b, Icarus 145, 53–63). Orbital elements at 1 AU are presented and discussed. These results have not been corrected for perturbation effects such as radiation pressure, Poynting–Robertson drag, attraction by the giant planets, and photoelectric charging effects. So far, over 7700 detections obtained during November 1997 and 3500 during the November 1998 observation campaigns have been analyzed. The observing periods included the Leonids meteor shower, but none of the orbits are recently derived from it. Out of these detections, we present details of over 1500 orbits with eccentricities less than unity. These orbits show (a) a depletion of postperihelion particles with small perihelion distance, suggesting the possibility of collisional and thermal destruction, and (b) an enhancement of particles with perihelia in the zone between Mercury and Venus. Also discussed are 40 β-meteoroids (with radii less than 0.5 μm) dynamically related to the elliptical orbit population with q<0.7 AU. We interpret the latter results on the basis of Poynting–Robertson drag and the electromagnetic resonant effects proposed by G. E. Morfill and E. Grün (1979, Planet. Space Sci. 27, 1269–1282). Comparison with previous data sets indicates that most of the AO micrometeoroid orbits are well randomized and that association with a particular parent body is unlikely.

Leonid electrophonic bursters

We investigate the conditions under which Leonid meteoroids might generate short duration (burster) electrophonic sounds. A first order theory is employed to estimate the approximate electron number density in the meteoroid ablation column as a function of time. Using the threshold conditions discussed in an earlier communication (Beech & Foschini [CITE]) we find that Leonid meteoroids more massive than about 0.1 kg can potentially generate short duration electrophonic bursters.

Sporadic-E associated with the Leonid meteor shower event of November 1998 over low and equatorial latitudes

Abstract. Rapid radio soundings were made over Ahmedabad, a low latitude station during the period 16–20 November 1998 to study the sporadic-E layer associated with the Leonid shower activity using the KEL Aerospace digital ionosonde. Hourly ionograms for the period 11 November to 24 November were also examined during the years from 1994 to 1998. A distinct increase in sporadic-E layer occurrence is noticed on 17, 18 and 19 November from 1996 to 1998. The diurnal variations of f0Es and fbEs also show significantly enhanced values for the morning hours of 18 and 19 November 1998. The ionograms clearly show strong sporadic-E reflections at times of peak shower activity with multiple traces in the altitude range of 100–140 km in few ionograms. Sporadic-E layers with multiple structures in altitude are also seen in some of the ionograms (quarter hourly) at Thumba, situated near the magnetic equator. Few of ionograms recorded at Kodaikanal, another equatorial station, also show sporadic- E reflections in spite of the transmitter power being significantly lower. These new results highlighting the effect of intense meteor showers in the equatorial and low latitude E-region are presented.Key words. Ionosphere (equatorial ionosphere) – Radio science (ionospheric physics)

High Spatial Resolution Observations of the 1998 and 1999 Leonid Meteors

AbstractWe observed the Leonid meteor storm in 1998 and 1999. The light curves extracted from the 2-dimensional images of the bright Leonid meteors clearly show the sub-structures, which are consistent with the generally accepted dustball meteor model (Hawkes &amp; Jones, 1975).

The Leonids Observation Project by High-School Students all over the World

We organized the Leonids observing network that comprised of 276 observation teams consisting of about 3,000 senior high-school students in Japan on Nov. 17 1998. We counted the visible meteors with our naked eyes. It was a simple method, but the many data enabled us to discuss the structure of the dust trail. However, the base-line is so short that we could not discuss the structure in full detail. In 1999, we organized a worldwide network of senior high-school students. The network is comprised of 307 teams from 23 countries. The base-line of our new project is the size of the Earth. We succeeded in making 20 hours continuous observations with this network. One of the observational teams in Tanzania encountered the Leonid meteor storm. We report on the scientific results and the educational aspects of these projects. (Web site: www.leonids.net/) (Leonids ‘98-’99 staff – co-authors – are A. Miyashita, M. Okyudo, H. Agata, T. Mizuno, T. Hamane K. Watanabe of Japan, C. Pennypaker, A. Gould, K. McCarron, G. Reagan and K. Meredith, of the U.S.A.)

Astronomy Educational Activity in Jordan

Throughout the last three millennia the area of Jordan, as part of the Arab World, has a rich history in the foundation and development of astronomy. Jordan today is pro-active in developing community programmes of education. I will describe the outreach programmes and community participation that I experienced during my attendence in Jordan at a conference timed to coincide with the Leonid Meteor Storm of November 1999.

Monitoring the moon's transient atmosphere with an all-sky imager

Abstract An indispensable tool in terrestrial aeronomy, all-sky imaging has recently been shown to be useful in studies of the Moon's exosphere. Two days after the peak of the 1998 Leonid meteor shower, an extended region of neutral sodium emission was detected in the night sky using a bare-CCD imaging system. The feature was found to be a train of sodium gas originating from the Moon. Subsequent observations indicate the feature is normally visible (max. brightness ∼15–90 Rayleighs (R)) during nights near the time of new Moon. Monthly monitoring of the feature using an all-sky system can provide useful information about the time-variability of the lunar atmosphere. Several processes are believed to be responsible for the production of lunar Na and evidence is presented indicating that two of these processes were each responsible for the observed brightness enhancements of the sodium feature on two separate new Moon periods in January and March 2000.

A Bacterial ‘Fingerprint’ in a Leonid Meteor Train

A recently observed broad 3.4 μm spectral ‘fingerprint’ in a persistent Leonid meteor train at a height of 83km is likely to be due to emission of surrounding mesospheric bacteria heated by the passage of an incandescent fireball.

Light Flashes Caused by Leonid Meteoroid Impacts on the Lunar Surface

In November 1999, light flashes were recorded on the Moon at the peak of the Leonid stream activity. It is likely that they were produced by the impacts of the stream particles on the lunar surface. In the present work the impacts of cometary particles are studied by solving a two-dimensional radiative-gasdynamic problem for particles of different sizes and densities; the flux of radiation of postimpact hot gas and plasma is calculated, and the luminous efficiencies are estimated, as are the sizes of the particles which could produce the observed flashes.

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NEWS

THE LEONID METEOROID SHOWER: LESSONS LEARNED FROM 1997 AND PLANS FOR 1998–2001

This paper discusses the upcoming Leonid meteoroid storm and its effects on spacecrafts. All satellites will be hit by tiny meteoroids but most of them will cause no problem. Penetration of spacecraft components is less of a threat than the plasma-related effects — ground currents and communication noise arising when impact-generated plasma strikes the antennae. Results from the 1997 monitoring campaign suggest that the storm intensity will be less than previously believed but sufficiently large uncertainties in both the number of meteoroids and the impact phenomenology that spacecraft owners and operators are urged to review the mitigation options presented in the paper and develop their own plans.

Catch a falling star this weekend

Stargazers may be in for a treat this weekend as the Earth takes its annual trip through the Leonid meteor belt. .