Leonid Meteor Research Articles

Leonid meteor spectrum from 110 to 860 nm

During the Leonid meteor shower on 18 November 1999, the five spectrographic imagers onboard the Midcourse Space Experiment (MSX) satellite recorded the first complete meteor spectra from 110 to 860 nm. The observation occurred at 00:23:36.2 UT, at which time the satellite was pointed at a tangent altitude of 100 km over 37.2°N and 78.2°E. The spectrograph slits were oriented approximately parallel to the horizon at a tangent altitude of 100 km, and the meteor passed approximately perpendicular through the slits’ fields of view. All five spectrographic imagers observed the passage of a bright object ( m v < −2.8 at 100 km) and each recorded several frames of data. In the visible, common meteor emissions were observed from iron, sodium, and oxygen. However, the ultraviolet spectrum displayed a wealth of more intense features, some of which actually caused saturation in the spectrographs. The most intense features appeared between 220 and 300 nm and are attributed to neutral and singly ionized iron and ionized magnesium. Some unknown emissions, possibly from an unidentified molecular species such as iron oxide, appear between 180 and 220 nm. In the far ultraviolet from 110 to 130 nm, oxygen and nitrogen features appear in the spectrum, with some features from ionized iron and magnesium. In particular, the FUV spectrum showed an intense emission from hydrogen Lyman alpha and a much weaker emission from what appeared to be neutral carbon. The atmospheric emissions can be associated with the heating within the meteor shock, while the metallic emissions originate from the fireball of the meteor proper. The ultraviolet emissions were much stronger than those in the visible and near-infrared parts of the spectrum. The energy of emissions in the ultraviolet (110 < λ < 337 nm) exceeded the energy of the visible (337 < λ < 650 nm) by a factor of at least 5.

The Composition of the Y2K Meteor

During the Leonid meteor shower of November 1999 a very bright meteor train, subsequently called the Y2K meteor, was observed. Analysis of the trajectory of the meteor suggests that it was composed of two distinct materials. The bulk of the meteor was composed of a comet-like material, while a much smaller fraction was of a denser carbonaceous material. A simple model is used to analytically determine the mass of the meteor fragments.

Optical Imaging of the Radiant Points of Leonids during the 2001 Storm with the 105 cm Kiso Schmidt Telescope

Abstract We report on the results of CCD imaging of the radiant points of Leonids with the 105 cm Kiso Schmidt telescope during its storm in 2001. The center coordinates of the observed field were $\alpha(\mathrm{J}2000.0) = {10{}^{\mathrm {h}}17{}^{\mathrm {m}}02\rlap {.}{}^{\mathrm {s}}4}$ and $\delta(\mathrm{J}2000.0) = + {21{}^{\mathrm {\circ }}37{}^{\mathrm {\prime }}48\rlap {.}{}^{\mathrm {\prime \prime }}0}$, corresponding to the center position between the two radiant points originating from dust trails created by the 1699 and 1866 returns of the Comet 55P/Tempel–Tuttle (McNaught, Asher 2001; WGN, 29, 156). Six CCD images having a field of view of ${51\rlap {.}{}^{\mathrm {\prime }}2} \times {51\rlap {.}{}^{\mathrm {\prime }}2}$ were obtained successively from 16h 58 m to 18h 28 m on November 18 (UT) in order to cover the two expected peaks of activity of the distinct radiant points. A limiting surface brightness of $25.93 \,\mathrm{mag} \,\mathrm{arcsec}^{-2}$, i.e., the $1\,\sigma$ noise level of the sky background, was achieved in each image. As a result, we detected only one faint Leonid meteor which most likely originated from a dust trail created by the 1866 return. The integrated total magnitude of the meteor is $m_{V}=18.34\pm 0.34 \,\mathrm{mag}$ on the image. Assuming a duration time of 0.1–1 s, we estimate the magnitude at the maximum luminosity of this meteor to be $9.70\pm 1.59 \,\mathrm{mag}$. This corresponds to a photometric mass of $(2.65^{+13.5}_{-2.22})\times 10^{-10} \,\mathrm{kg}$, which makes this meteor one of the faintest and smallest Leonids detected so far.

Observations on Stratospheric-Mesospheric-Thermospheric temperatures using Indian MST radar and co-located LIDAR during Leonid Meteor Shower (LMS)

Abstract. The temporal and height statistics of the occurrence of meteor trails during the Leonid meteor shower revealed the capability of the Indian MST radar to record large numbers of meteor trails. The distribution of radio meteor trails due to a Leonid meteor shower in space and time provided a unique opportunity to construct the height profiles of lower thermospheric temperatures and winds, with good time and height resolution. There was a four-fold increase in the meteor trails observed during the LMS compared to a typical non-shower day. The temperatures were found to be in excellent continuity with the temperature profiles below the radio meteor region derived from the co-located Nd-Yag LIDAR and the maximum height of the temperature profile was extended from the LIDAR to ~110 km. There are, how-ever, some significant differences between the observed profiles and the CIRA-86 model profiles. The first results on the meteor statistics and neutral temperature are presented and discussed below. Key words. Atmospheric composition and structure (pres-sure, density, and temperature) History of geophysics (at-mospheric sciences) Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Prediction of the 2001 Leonid activity and an assessment of the spacecraft impact hazard

Different maxima in the Leonid activity observed in the same year can be identified as due to dust particles ejected during different perihelion passages of the parent comet, 55P/Tempel–Tuttle. This is because the ecliptic intersections of trajectories of particles that were ejected during different comet apparitions lie well separated in the ecliptic plane. For November 2001, we determine the ecliptic intersection points of particles originating from various apparitions of 55P/Tempel–Tuttle and thus predict the times of maximum Leonid activity. By comparing this year9s configuration with the past, we also give an estimate of the flux that might be expected in 2001. As light flashes due to Leonid impacts on the Moon can be detected on Earth, we give the times of closest approaches of dust trails to the Moon. By comparing the predicted Leonid meteoroid flux on the Earth9s atmosphere with the flux of sporadic meteoroids, we estimate that the hazard of a Leonid impact on a spacecraft in low–Earth orbit is low. However, the densest part of the Leonid trails will not reach Earth, but will cross the geo–stationary orbit (GEO) ring. The impact risk will reach its maximum for GEO satellites at longitudes between 35° and 160° W between 17.00 and 20.00 UT on 18 November 2001. While the overall risk of major damage is still relatively low, this period undoubtedly represents the greatest impact risk to spacecraft since the beginning of the space–age.

An observation of a fast external atmospheric acoustic‐gravity wave

In November 1999 a new near‐IR airglow imaging system was deployed at the Starfire Optical Range outside of Albuquerque, New Mexico. This system allowed wide angle images of the airglow to be collected, with high signal to noise, every 3 seconds with a one second integration time. At approximately 1000 UT on November 17, 1999, a fast wavelike disturbance was seen propagating through the OH Meinel airglow layer. This wave had an observed period of ≈215 seconds, an observed phase velocity of ≈160 m/s and a horizontal wavelength of ≈35 km. This phase velocity is among the fastest yet reported using an imager viewing the OH Meinel bands, while the wave period is among the shortest. Simultaneous Na lidar wind and temperature data from 80 to nearly 110 km altitude allow the intrinsic properties of the wave to be calculated. The Einaudi and Hines [1970] WKB approximation for the acoustic‐gravity wave dispersion relation was used to calculate the wave's intrinsic properties. Using this approach indicates that the observed disturbance was an external acoustic wave in the 90 to 107 km altitude region and an external gravity wave at other altitudes between 80 and 90 km. Using model atmospheric data for altitudes below and above this altitude regime indicates that the wave is essentially external everywhere except perhaps in narrow regions around 80 and 105–110 km. This is confirmed using a more exact full‐wave model analysis. The observations and model results suggest that this wave was not generated in the troposphere and propagated up to the mesosphere, but rather near 100 km altitude where it was possibly generated by a Leonids meteor.

Lightcurves of 1999 Leonid Impact Flashes on the Moon

Optical flashes observed on the night side of the Moon during the 1999 Leonid meteor shower have attracted the interest of astronomers. These flashes are attributed to high-velocity impacts of Leonid meteoroids on the lunar surface. Here, we report five lunar flashes detected over a 5.8-h observation period centered at 11:25 UT on Nov. 18, 1999, in Japan. The flashes are characterized by an abrupt brightening. Three flashes exhibited afterglows that remained visible for at least 50 ms, which is longer than the duration predicted for radiation from an impact-generated plasma cloud. We show that thermal radiation from hot droplets ejected from the lunar surface during high-velocity impacts could be the cause of the afterglows.

Observations of persistent Leonid meteor trails 3. The “Glowworm”

A spectacular, well‐observed Leonid meteor of visual magnitude −14.3 appeared on 17 November 1998 and left a lingering trail, dubbed the Glowworm, that was well studied. From a location on Kirtland Air Force Base, near Albuquerque, New Mexico, we obtained CCD images of the trail from 94 to 203 s after the meteor and recorded a video with an intensified camera for even longer. From information obtained with a sodium lidar half an hour after the meteor, we have determined that a gravity wave with a vertical wavelength of 2.4 km was responsible for the right‐angled appearance of the trail. The trail ended abruptly at 85 km, and its uppermost altitude may have been no greater than 91 km. We designate the Glowworm a Type I trail: one that is wide (1 km), cloudy in appearance, has high diffusion rates (800 m2 s−1), high total line emission rates (1.5×1018 photons m−1 s−1), and is optically thicker than Type II trails. The lower parts of the Diamond Ring, another Leonid lingering trail that appeared 38 min earlier than the Glowworm, define the Type II trails, which appear as narrow, optically thinner parallel trails, with low diffusion rates (12 m2 s−1) and total line emission rates (1–3×1016 photons m−1 s−1). No explanation is offered for the two orders of magnitude difference in these quantities. The Glowworm meteor produced infrasound [ReVelle and Whitaker, 1999], from which a meteoroid mass estimate of 522 g was made. We compare our photometry to a detailed numerical modeling of the shape of the trail and emission from the Glowworm made by Zinn et al. [1999], who find that the largest contributors to emission recorded by our CCD and video cameras are atmospheric O2 vibrational bands. Compared to our measurements, their calculated emission is too high by two orders of magnitude, but since most of O2 emission may be absorbed by atmospheric O2 before it reaches the ground, this may indeed be the primary contributor to the observed flux. Although the calculations of Zinn et al. lead to a hollow cylinder appearance which may be appropriate for the Glowworm, it is not pronounced enough to account for the complete darkness between the parallel structures seen in Type II trails. An upper limit to backscattering from dust of 3.7 × 10−5 of the expected return was found from directing a 180 W copper vapor laser at the Glowworm.

Extraterrestrial samples from low Earth orbits: techniques for their collection and analysis

In the context of dust samples collections in space, the COMET experiment (Collecte en Orbite de Matière ExtraTerrestre) was proposed for the first time in 1982. The idea of such an experiment was to collect grains with identified cometary parent body, instead of mixing all extraterrestrial contributions present in low Earth orbit. It was thus proposed to install collectors inside hermetic boxes, to have these boxes mounted outside a space station, orbiting the Earth and to have the capability of choosing the time and duration of the collection. Since 1985, the COMET experiment has been exposed three times to space (COMET-1, in October 1985 during the encounter of the Earth with the Draconid meteor stream; the EUROMIR-95 instrument, exposing collectors, during the crossing by the Earth of the Orionid meteor stream associated to comet P/Halley and, in November 1998, during the crossing by the Earth of the Leonid meteor stream associated to comet Temple-Tuttle, COMET-99). Specific collection techniques, and corresponding analytical procedures have been developed. The collected particles are the only ones accessible in the laboratory with a known cometary origin, before the return to Earth (2006) of the Stardust mission, which will collect cometary grains in the tails of comet Wild 2. Such a challenge justifies the tremendous efforts brought into play, and that are summarized here.

And just when you thought that the Leonid meteor storm held no more surprises: The 2001 storm

Editorials: F.J. M. Rietmeijer: And just when you thought that the Leonid meteor storm held no more surprises: The 2001 storm.

Wide-Field TV Observation of the Leonid Meteor Storm in 2001: Main Peak over Japan

We carried out a wide-field TV observation of the strong activity of the Leonid meteor shower from $ {17{}^{\mathrm {h}}17{}^{\mathrm {m}}}$ UT through $ {20{}^{\mathrm {h}}20{}^{\mathrm {m}}}$ UT on 2001 November 18. We detected 869 Leonid meteors, along with 32 non-Leonids. A broad peak of the activity was recognized at around $ {18{}^{\mathrm {h}}25{}^{\mathrm {m}}}$ UT, when the peak influx rate of meteoroids was $ 1.4 \times 10^{-5} \,\mathrm{km}^{-2} \,\mathrm{s}^{-1}$ ($ \mathrm{mag} \le +3$). The activity of this main peak was comparable to that of a storm observed in 1999 over Europe. The activity of this peak was rich in bright meteors, including fireball class. The magnitude distribution index was $ 1.5 \pm 0.3$ ($-3 \le \mathrm{mag} \le +1$). The relationship between the observed peak and several theoretical predictions is discussed. We also discuss an “outburst”, which consisted of at least 15 faint meteors which appeared within four seconds at $ {17{}^{\mathrm {h}}56{}^{\mathrm {m}}22{}^{\mathrm {s}}}$.

An analysis of photographic observations of the Leonid meteoric shower in 1999

Photographic observations of meteors can provide more information than visual observations. In this paper, two photographs of Leonid meteoric shower taken on 1999 November 19 have been analyzed. The maximal angular velocity of meteoroids that cancan show up on films has been evaluated. The elevation of the beginning point, angular distance between the ending point and the radiant, angular velocity and arc length of the meteor's path are calculated for the two observed meteors. In addition, the observed short duration of about 0.65 second for the ablation of the meteoroids in the atmosphere means that the path length of ablation is about 40–50 kilometers. Through digitized processing of the photographs, photographic magnitudes of −10.3±0.2 and −4.8 ± 0.2 have been measured for the two Leonid meteors, from which their masses and electric line densities can be derived. The procedure given in this paper could be used for photographic observations of other meteors. We also discuss how to select a camera lens for meteor observations.

Comparison between Leonid meteor shower observations during 1998–2000

Observations for the Leonid meteor shower from the Gaomeigu station of Yunnan Observatory during 1998–2000 are analyzed in this paper. We introduce a new statistical quantity zenithal hourly mass rates (ZHMR) to deal with the mass flow of a meteoroid stream. The variations of r, ZHR and ZHMR are given. During our observations, ZHMR had often a value of the order of 10 −6– 10 −3 g/km 2 h . The variation of r may be more strong and frequent in 1998 than in 1999, but in most cases, it was about 2.0. Interesting phenomena like filamentary structure was observed in ZHR and mass influx profiles. In our observations, the filamentary structure has no periodic variation. In general, the ZHMR and ZHR would show different behaviour and go to their maximum at different times. The ZHMR may become a new statistic to support comparisons between different observers, and might be a more useful quantity for predictions. In 1999, the dust trails of 4- and 5-revolution (rev) seem to leave nothing at the exact predicted time. At most, we estimate the ZHR introduced solely by the 4-rev. trail should not be over 50.

Multi-station electro-optical observations of the 1999 Leonid meteor storm

Single- and double-station video observations of the 1999 Leonid shower made from Israel are presented. A total of 232 double-station Leonids had trajectories computed. Additionally, some 2500 single-station Leonids were used to measure the Leonid storm flux and mass distribution in the interval from 0.5– 3 UT 18 November 1999. The height distribution for storm Leonids of average mass ∼10 −6– 10 −7 kg indicates that the ablation zone is approximately Gaussian-shaped with best-fit mean begin, maximum brightness and end heights of 123.3±0.7, 107.3±0.42 and 95.0±0.56 km respectively. The peak flux at the time of the storm was found to be 0.81±0.06 meteoroids km −2 hr −1 Mv<+6.5. using 15 min binning and 0.99±0.11 meteoroids km −2 hr −1 Mv<+6.5 for 3 min intervals. The smaller temporal resolution reveals a broad plateau in flux lasting from approximately λ 0=235.276–235.285° (J2000.0). At least one significant feature in the rate curve is apparent near 235.272°, which we suggest is associated with material released in 1932. The video mass distribution index over the course of the Leonid storm was found to be constant near s=1.75. The peak time of the storm estimated from 15 min sampling of the flux profile is near 235.283±0.005° (1h58m±7m) while 3 min resolution data place the maximum at 235.281±0.003° (1h55m±4m). The mean radiant position at the time of the storm was found to be α=153.1±0.1° and δ=21.5±0.2° (J2000), with some hint of a more compact radiant grouping within the range α=153–154° and δ=21–22°. We do not find evidence for any significant high altitude Leonid population at video masses despite biasing one camera pair to an intersection altitude of 160 km .

Motions of dust particles ejected from a comet with application to Leonid meteoroid

An analytical expression for the orbit of a dust particle ejected from a comet is derived as the two-body problem by including solar radiation pressure effects. Then deviations of the semi-major axis, the eccentricity and the epoch of the perihelion passage of the particle from those of the comet are expressed as functions of a parameter depending on the ejection velocity, the size of the particle and the true anomaly at the ejection point. Furthermore, numerical values are computed for comet 55P/Tempel-Tuttle which has produced Leonid meteor showers. Finally, perturbations due to Jupiter, Saturn and Uranus are roughly computed and an idea to predict meteor showers is proposed.

Comet tempel-tuttle and the recent Leonid meteor shower

As one of the famous meteor showers the Leonid meteor shower had the most spectacular bursts in history. Since 1998 a new series of activity of the Leonids has been coming. What will it be in recent years and in the future? According to different references, the levels of the showers in history are reviewed and discussed in this paper. Especially, the diagram of CEOS (the Comet-Earth Orbits Separation) versus T E-C (the time gap of the Earth following the Comet) is analyzed. It is found that almost all the meteor storms are located in an inclined square, and the strongest storms are in a curved strip. The boundaries of the square have a slope of about 15 m s −1. The sizes of meteoroids calculated from this velocity are also reasonable. This means that the particles colliding with the Earth have a limited velocity to drift off its original orbit. With larger CEOS, the longer time interval after the comet passage would be needed for a possible storm. The width of this square indicates that the stronger Leonid showers would never be seen on more than about four consecutive years. In one cometary return, the percentage of bright meteors will decrease year by year. These facts could be explained by a model of the formation of a cometary dust tail, including the motion, dispersion, and breaking up of dust particles. Prediction could be made with this square region. We may have Leonid showers in 1998–2000 with a peak in 1999, and after AD 2000, one has to wait another century before significant displays will once again appear.

Characterization of Leonid meteor head echo data collected using the VHF‐UHF Advanced Research Projects Agency Long‐Range Tracking and Instrumentation Radar (ALTAIR)

The Leonid meteor shower, which was predicted to hit storm‐like activity on 17 November 1998, was observed using radar and optical sensors at the Kwajalein Missile Range in order to study potential threats to orbiting spacecraft. Meteor head echo data were collected during the predicted peak of the “storm” primarily using the Advanced Research Projects Agency Long‐Range Tracking and Instrumentation Radar (ALTAIR). ALTAIR is a dual‐frequency radar at VHF (160 MHz) and UHF (422 MHz) that is uniquely suited for detecting meteor head echoes due to high sensitivity, precise calibration, and the ability to record radar data at a high rate (Gb/min). ALTAIR transmits right‐circular (RC) polarized energy and records left‐circular (LC) sum, RC sum, LC azimuth angle difference, and LC elevation angle difference channels; these four measurements facilitate the determination of three‐dimensional target position and velocity as a function of radar cross section and time. During the predicted peak of the storm, ALTAIR detected 734 VHF head echoes in 29 min of data and 472 UHF head echoes in 17 min of data, as well as numerous specular and nonspecular ionization trails. This paper contains analysis on the head echo data, including dual‐frequency statistics and the variability of head echo decelerations. We also include results from the analysis of the radius‐density parameter, which shows a strong correlation with deceleration.

Contour Observations of the Leonid Shower in 1999

Contour visual observations of the Leonid meteor shower were made on December 18, 1999 by the method in which different groups of observers counted meteors in zenith, near the horizon, and observed through binoculars to study the luminosity function and the space density of the swarm. The luminosity function was obtained in the range of magnitudes from –8m to +9m. Over a wide range of magnitudes, the luminosity function is found to be nonlinear and is adequately approximated with a second-order curve. The logarithm of the meteor space density Φ(m) reaches saturation at about 10m, indicating that particles that give rise to meteors fainter than 10m are absent in the swarm. The meteor stream reached its activity peak at a solar longitude of 235°, 287 (2h05m UT). The peak visual zenithal hourly rate was about 7000 per one observer over an averaging interval of 1 min. The swarm space density increased by a factor of 6 within 0.5 hours and exceeded 600 particles per 109 km3 for meteors brighter than +4m. In the peak night, the luminosity-function exponent demonstrates no regular trend and reflects the intercepting of certain swarm clouds by the Earth.

Leonid fluxes: 1994–1998 activity patterns

Abstract— The Leonid meteor shower was observed worldwide in 1998 November in an intensive campaign without precedent. During this international effort ∼35 500 meteors were reported by members and collaborators of the International Meteor Organization (IMO) using a standard methodology. Despite the absence of a meteor storm in 1998, the rich observational data allow us to obtain a detailed unprecedented knowledge of the stream structure between 1994 and 1998.

Flux of very faint Leonid meteors observed with a 3 meter liquid mirror telescope intensified charge‐coupled device system

Abstract— We have used a 3.0 m diameter liquid mirror telescope (LMT) coupled to a microchannel plate image‐intensified charge‐coupled device (CCD) detector to study the 1999 Leonid meteor shower. This is the largest aperture optical instrument ever utilized for meteor detection. While the observing system is sensitive down to stars of +18 astronomical magnitude under optimum conditions, when corrections for meteor motion are applied the majority of the meteors collected fall in the absolute magnitude range from +5 to +10, corresponding to photometric masses from about 10−7 to 10−9 kg. This is largely due to the fact that the field of view of the LMT was only 0.28°, so that only a small portion of the luminous meteor trail was recorded. While the flux of these small (1.4 times 10−9 kg) Leonid meteors is low (on the order of one Leonid meteor per hour per square kilometer perpendicular to the Leonid), we do have clear evidence that the Leonid stream contains particles in the mass range studied here. The data showed a possibly significant peak in Leonid flux (9.3 ± 3.5) for the 1 h period from 11:00 to 12:00 u.t. 1999 November 17 (solar longitude 234.653 to 234.695, epoch 2000.0), although the main trend of these results is a broad low‐level Leonid activity. There is evidence that small meteoroids are more widely distributed in the Leonid stream, as would be expected from cometary ejection stream models. As would be expected from an extrapolation of mass distribution indices for brighter meteors, the vast majority of meteors at this size are sporadic. The LMT is a powerful detector of sporadic meteors, with an average non‐Leonid detection rate of more than 140 meteor events per hour.