Meteor Observations Research Articles

The calculation of meteor motion parameters based on the single station TV observations

Recently, television observations of meteors have steadily replaced photographic observations. Television recording with short exposures is a close analog of a photographic survey with a rotary shutter in the form of a system of set time marks on the meteor track. Each meteoric event is a series of recordings of separate phases of the motion of a meteor. This allows for the use of the geometric method for the determination of the motion parameters of meteors. In this work, a critique is given regarding the concept proposed by K.P. Stanyukovich in 1932–1939, and a mathematical justification of the geometric method of the analysis of the television images of meteors is given.

Gravity wave flux retrievals using meteor radars

The ability of all‐sky interferometric meteor radars to measure mean wind and high‐frequency gravity wave wind perturbations from meteor radial velocities is assessed. A Monte‐Carlo technique that models line‐of‐sight meteor wind measurements with realistic errors in angle‐of‐arrival and range is used to investigate uncertainties in mean wind and gravity wave wind parameters as a function of meteor echo rate. It is shown that mean horizontal wind speeds are recovered with reasonable accuracy at meteor rates as low as 10 hr−1. Mean‐square horizontal wind perturbation can be derived with relatively little averaging, but momentum fluxes are recovered with much less accuracy, which means that considerable averaging is required to produce meaningful values. Results are illustrated using meteor wind radar observations taken over a 30‐day period in January–February 2006 in Northern Australia.

Meteoroid mass determination from underdense trails

This paper presents a new method to estimate the meteoroid mass from specular meteor observations. The basis of this method is the ability of a standard meteor radar to measure meteoroid head velocity, the height of detection, the source radiant (on a statistical basis) and the electron line density in the specular point. The electron line density can be related to the mass ablation rate by applying an ionization efficiency model. Selecting potential meteoroids from the Geminid meteor shower according to their source radiant and velocity distribution and combining all of these measurements with a numerical single body meteor ablation model permits to compute the meteoroid mass, deceleration and temperature in the specular point. The pre-atmospheric properties of an average meteoroid are estimated by fitting the single body ablation model to the estimates of the meteor parameters in the specular points.

A method for the determination of meteor stream membership based on the results of the single-station television observations used at INASAN

Massive television observations of meteors aimed at verifying the existing and finding new meteor streams create the task of the reliable preliminary determination of the detected meteor membership in a particular known stream. The mostly widely used method of meteor identification is connected with the estimation of the distance between the great circle of the meteor and the point of the examined radiant. Often observers perform this estimation without checking the possibility that the same meteor belongs to another stream. When several streams occur simultaneously, many meteors can be members of two or more streams. When the determination of the meteor membership is done in a subjective way, it may lead to an overestimation of strong streams’ and an underestimation of weak streams’ activity. In this work, we describe a method and algorithm for the determination of the meteor membership in known streams which were tested using real television observations and were successfully used at INASAN. This algorithm is almost completely automatic and allows for the obtainment of additional information regarding meteor streams. We also show some results of the processing of 2254 meteors observations obtained with the FAVOR camera from July 31, 2006 to October 21, 2006 using the proposed method. The work is part of the program for the creation of the Verified Catalogue of Meteor Streams.

Extensive meteoroid fragmentation in V/UHF radar meteor observations at Arecibo Observatory

New 46.8/430 MHz (V/UHF) radar meteor observations at Arecibo Observatory reveal many previously unreported features in the radar meteor return that are consistent with meteoroid fragmentation. These signature features—observed at both V/UHF—include strong intra‐pulse and pulse‐to‐pulse fading as the result of interference between or among multiple meteor head‐echo returns and between head‐echo and impulsive “flare” event “trail‐echoes”. A few events are suggestive of differential ablation. These V/UHF radar observations are particularly useful as coaxial beams enable common volume observations that remove much ambiguity in the interpretation of the observations in terms of meteoroid fragmentation. These results, combined with simple modeling and two 500 sample statistical studies, lead us to conclude that a majority of the ∼17,000 AO radar meteor events included in this study exhibit fragmentation—manifested as non‐uniform lightcurves—implying that the form of meteoroid mass flux into the upper atmosphere goes well beyond simple ablation.

The solar cycle effect on the atmosphere as a scintillator for meteor observations

AbstractWe discuss using high solar cycle atmospheric conditions as sensors for observing meteors and their properties. High altitude meteor trails (HAMTs) have sometimes been observed with HPLA (High Power Large Aperture) radars. At other times they are not seen. In the absence of systematic studies on this topic, we surmise that the reason might be differing atmospheric conditions during the observations. At EISCAT HAMTs were observed in 1990 and 1991. Very high meteor trails were observed with Israeli L-band radars in 1998, 1999 and 2001. Through the Leonid activity, around the latest perihelion passage of comet Tempel-Tuttle, optical meteors as high as 200 km were reported. This was partly due to new and better observing methods. However, all the reported periods of high altitude meteors seem to correlate with solar cycle maximum. The enhanced atmospheric and ionospheric densities extend the meteoroid interaction range with the atmosphere along its path, offering a better possibility to distinguish differential ablation of the various meteoric constituents. This should be studied during the next solar maximum, due within a few years.

Genetic-Algorithm-Based Parameter Estimation Technique for Fragmenting Radar Meteor Head Echoes

Meteoroid fragmentation presents a serious problem for Doppler estimation using Fourier transform techniques. Radar returns from multiple closely spaced bodies traveling at nearly identical speeds result in an interference pattern which makes it difficult to estimate properties of individual bodies by traditional techniques. Here, we present a genetic-algorithm-based procedure to determine the properties of the individual fragments, such as relative scattering cross section, speed, and deceleration. The radar meteor observations presented here were made using the Poker Flat (Alaska) Incoherent Scatter Radar operating at 449.3 MHz.

Diurnal variation of non-specular meteor trails

Abstract. We present results of simulated radar observations of meteor trails in an effort to show how non-specular meteor trails are expected to vary as a function of a number of key atmospheric, ionospheric and meteoroid parameters. This paper identifies which geophysical sources effect the variability in non-specular trail radar observations, and provides an approach that uses some of these parameter dependencies to determine meteoroid and atmospheric properties based upon the radar meteor observations. The numerical model used follows meteor evolution from ablation and ionization to head echo plasma generation and through formation of field aligned irregularities (FAI). Our main finding is that non-specular meteor trail duration is highly sensitive to the presence of lower thermospheric winds or electric fields and the background ionospheric electron density. In an effort to make key predictions we present the first results of how the same meteoroid is expected to produce dramatically different meteor trails as a function of location and local time. For example, we show that mid-latitude trail durations are often shorter lasting than equatorial trail observations because of the difference in mid-latitude wind speed and equatorial drift speed. The simulated trails also account for observations showing that equatorial nighttime non-specular meteor trails last significantly longer and are observed more often than daytime trails.

Advanced SuperDARN meteor wind observations based on raw time series analysis technique

The meteor observation technique based on SuperDARN raw time series analysis has been upgraded. This technique extracts meteor information as biproducts and does not degrade the quality of normal SuperDARN operations. In the upgrade the radar operating system (RADOPS) has been modified so that it can oversample every 15 km during the normal operations, which have a range resolution of 45 km. As an alternative method for better range determination a frequency domain interferometry (FDI) capability was also coded in RADOPS, where the operating radio frequency can be changed every pulse sequence. Test observations were conducted using the CUTLASS Iceland East and Finland radars, where oversampling and FDI operation (two frequencies separated by 3 kHz) were simultaneously carried out. Meteor ranges obtained in both ranging techniques agreed very well. The ranges were then combined with the interferometer data to estimate meteor echo reflection heights. Although there were still some ambiguities in the arrival angles of echoes because of the rather long antenna spacing of the interferometers, the heights and arrival angles of most of meteor echoes were more accurately determined than previously. Wind velocities were successfully estimated over the height range of 84 to 110 km. The FDI technique developed here can be further applied to the common SuperDARN operation, and study of fine horizontal structures of F region plasma irregularities is expected in the future.

Densities and porosities of meteoroids

Using a physical theory of meteors and on the basis of the results of double-station photographic observations of meteors in Dushanbe (Tajikistan), Kiev, and Odessa (Ukraine), the mean mineralogical and bulk densities of meteoroids belonging to nine meteoroid streams and sporadic background are determined. The mean mineralogical densities of meteoroids range from 2.2 g cm-3 (Perseids) to 3.4 g cm-3 (Quadrantids, δ -Aquarids, and α -Capricornids). The meteoroid bulk densities δ , which were determined according to the theory of quasi-continuous fragmentation of meteoroids in the Earth's atmosphere, vary from 0.4 g cm-3 (Leonids) to 2.9 g cm-3 (Geminids). Using the relation between bulk density and mineralogical density the porosity of meteoroids was estimated. The Geminid meteoroids are found to have the lowest porosity, while the Leonid and Draconid meteoroids have the most porous structure (83%). These results confirm the porous-structure nature of meteoroids' parent bodies i.e. comets and asteroids.

Seismic observations of meteors: Coupling theory and observations

Over the last century, seismic instruments have recorded, with increasing frequency, the ground motion produced by meteorically generated shock waves striking the Earth's surface. In this review, the history of meteor‐related seismic signals is discussed, along with documented waveform characteristics, source mechanisms, air‐ground coupling phenomena, and kinematic methods of determining meteor trajectories and event locations. Uncertainties in the mechanics of air‐ground coupling, however, have left methods of measuring meteor source energy underdeveloped. To date, coupling of acoustic waves directly with the Earth's surface represents the bulk of the observed meteor‐related seismic signals, while precursory and impact‐related seismic waves remain an observational rarity. With proliferation of infrasound and seismic monitoring systems, new opportunities exist to explore the relationship between Earth's atmosphere and surface. Continued study of meteor seismology will lead to new methods to constrain energies, sizes, and fluxes for moderately (cm to m) sized meteoroids on Earth and potentially on Mars.

On the validity of the ambipolar diffusion assumption in the polar mesopause region

Abstract. The decay of underdense meteor trails in the polar mesopause region is thought to be predominantly due to ambipolar diffusion, a process governed by the ambient temperature and pressure. Hence, observations of meteor decay times have been used to indirectly measure the temperature of the mesopause region. Using meteor observations from a SKiYMET radar in northern Sweden during 2005, this study found that weaker meteor trails have shorter decay times (on average) than relatively stronger trails. This suggests that processes other than ambipolar diffusion can play a significant role in trail diffusion. One particular mechanism, namely electron-ion recombination, is explored. This process is dependent on the initial electron density within the meteor trail, and can lead to a disproportionate reduction in decay time, depending on the strength of the meteor.

Seasonal and diurnal variability of the meteor flux at high latitudes observed using PFISR

We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena; for example, it could be the source of meteoric smoke that is thought to act as condensation nuclei in the formation of ice particles in the polar mesosphere. The observations presented here were performed for full 24-h periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes [Janches, D., Heinselman, C.J., Chau, J.L., Chandran, A., Woodman, R., 2006. Modeling of the micrometeor input function in the upper atmosphere observed by High Power and Large Aperture Radars, JGR, 11, A07317, doi:10.1029/2006JA011628]. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected every day. We show that meteor rates, altitude, and radial velocity distributions have a large seasonal dependence. This seasonal variability can be explained by a change in the relative location of the meteoroid sources with respect to the observer. Our results show that the meteor flux into the upper atmosphere is strongly anisotropic and its characteristics must be accounted for when including this flux into models attempting to explain related aeronomical phenomena. In addition, the measured acceleration and received signal strength distribution do not seem to depend on season; which may suggest that these observed quantities do not have a strong dependence on entry angle.

Determination of day‐time OH emission heights using simultaneous meteor radar, day‐glow photometer and TIMED/SABER observations over Thumba (8.5°N, 77°E)

Simultaneous day‐glow photometer and meteor radar observations are used for determining the day‐time OH emission height for the first time over Thumba (8.5°N, 77°E). The meteor radar observations are extensively used to obtain the ambipolar diffusion coefficient (Da) profile in the 82–98 km height region and are compared with OH rotational temperature (TOH) measurements. The height profile of correlation coefficient between Da and TOH showed a maximum at 90 km. These ground based estimates are then compared with space based OH volume emission rate (VER) observations by TIMED/SABER satellite over this latitude, which showed an excellent agreement. Further, the temporal variation of OH emission heights showed tidal modulation of OH emission heights. The significance of the present results lies in determining the day‐time OH emission height for the first time using collocated radar and photometer observations, which will have implications in interpreting TOH in the MLT region.

Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR

In this work, we use a semi-empirical model of the micrometeor input function (MIF) together with meteor head-echo observations obtained with two high power and large aperture (HPLA) radars, the 430 MHz Arecibo Observatory (AO) radar in Puerto Rico (18°N, 67°W) and the 450 MHz Poker flat incoherent scatter radar (PFISR) in Alaska (65°N, 147°W), to study the seasonal and geographical dependence of the meteoric flux in the upper atmosphere. The model, recently developed by Janches et al. [2006a. Modeling the global micrometeor input function in the upper atmosphere observed by high power and large aperture radars. Journal of Geophysical Research 111] and Fentzke and Janches [2008. A semi-empirical model of the contribution from sporadic meteoroid sources on the meteor input function observed at arecibo. Journal of Geophysical Research (Space Physics) 113 (A03304)], includes an initial mass flux that is provided by the six known meteor sources (i.e. orbital families of dust) as well as detailed modeling of meteoroid atmospheric entry and ablation physics. In addition, we use a simple ionization model to treat radar sensitivity issues by defining minimum electron volume density production thresholds required in the meteor head-echo plasma for detection. This simplified approach works well because we use observations from two radars with similar frequencies, but different sensitivities and locations. This methodology allows us to explore the initial input of particles and how it manifests in different parts of the MLT as observed by these instruments without the need to invoke more sophisticated plasma models, which are under current development. The comparisons between model predictions and radar observations show excellent agreement between diurnal, seasonal, and latitudinal variability of the detected meteor rate and radial velocity distributions, allowing us to understand how individual meteoroid populations contribute to the overall flux at a particular location and season.

A new method of discovering new meteor showers from the IMO single-station video meteor database

It has been found that unknown meteor showers could be efficiently discovered from the single station video meteor database of the International Meteor Organization (IMO) by assuming the geocentric velocity and adjusting it within the dynamically permitted range. The mean geocentric velocities of new meteor showers can be obtained, as well as the coordinates of the radiants. The activity period and maximum time can also be obtained if there are sufficient shower meteors. All single station video meteor observations between February 13 and 17 (from 2000 to 2005) in IMO’s database are processed with this method. As a result, two new meteor showers, one near RA=245.10°, Dec=41.82° in Hercules and the other near RA=233.03°, Dec=17.04° in Serpenids, are discovered. Some dynamical characteristics of the new meteor showers are also determined. Considering the random nature on the selection of period in this work, it is expected that there are some more potential new meteor showers in IMO’s video database.

Annual and Diurnal Variation of Meteor Rates by the Forward-Scatter Radio Observation

Forward-scatter radio meteor observations have been made at Japan since 1996 using inexpensive and low-end equipment. The activity of some major meteor showers and the seasonal variability of sporadic meteors in 2006 are presented.

An analytic function of the two-dimensional probabilities of perception of the human eyes

The probability of perception is an indispensable quantity in the visual observation of meteors. Based on the data of a large number of double-counting observations, Koschack and Rendtel derived a table-listed average perception function P ( Δ m ) in 1990 and Wu gave it a fitting analytic function in 2005. In this paper, a fitting of the perception function in the two-dimensional field of view, P ( Δ m , R ) , is given. Both the new analytic function and each order of its derivatives have only a monodromy and are very smooth. This analytic function will be more essential and useful than the average function P ( Δ m ) and may be connected to the two-dimensional structure of the human eyes as an imaging system.

A semi‐empirical model of the contribution from sporadic meteoroid sources on the meteor input function in the MLT observed at Arecibo

In this paper, we present a modeling and observational study of the micrometeor input function with a focus on understanding how each of the extraterrestrial sporadic meteoroid sources contributes to the observed meteoric flux in the Mesosphere and Lower Thermosphere (MLT) atmospheric region. For this purpose, we expand the model presented by Janches et al. (2006) using a Monte Carlo technique and incorporating: 1) a widely accepted global mass flux, which is divided into different proportions among the known sporadic meteoroid sources as the initial input above Earth’s atmosphere; 2) contemporary knowledge on the source's velocity and radiant distributions; and 3) the full integration of the canonical meteor equations that describe the meteoroid entry and ablation physics. In addition, we constrain the initial input through a comparison of our modeled results with meteor observations obtained with the 430 MHz High Power and Large Aperture (HPLA) Arecibo radar in Puerto Rico that covers all seasons. The predicted meteor rates and velocity distributions are in excellent agreement with the observed ones without the need for any additional normalization factor. Our results indicate that although the Earth’s Apex centered radiant source, which is characterized by high geocentric speeds (∼55 km/s), appears to be ∼33% of the meteoroids in the Solar System at 1 AU, it accounts for ∼60% of the meteors observed by the Arecibo HPLA radar in the atmosphere. The remaining 40% of observed meteors originate mostly from the Helion and Anti‐Helion sources, with a very small, but constant during the day, contribution of the South and North Toroidal sources. These results also suggest that particles smaller than ∼10−3μg with slow velocities (<30 km/s) will not significantly ablate and never become observable meteors. The motivation of this effort is to construct a new and more precise MIF model needed for the subsequent modeling of the atmospheric phenomena related to the meteoric flux.

Techniques for positional measurements of telescopic meteor TV images

We present the results of our positional reduction of the observational material obtained using a meteor patrol based on a Schmidt telescope and a TV CCD detector. More that 1000 telescopic meteors were recorded in three years of meteor patrolling. Techniques for the cataloging and positional reduction of 3050 TV images with meteor trails are described. We have developed a technique for measuring the images of reference stars to determine the rectangular coordinates in the image frame. We discuss the achieved accuracy of determining the equatorial coordinates of reference and check stars by Turner’s method (of the order of a few arcseconds). We have developed software that allows the rectangular coordinates of meteor trajectory points to be determined after the meteor image reduction. These coordinates are used to determine the equatorial coordinates of the poles of the great circles of meteor trajectories (the angular length is not less than 15′ with an accuracy of at least 4′. We consider the possibility of using Stanyukovich’s method to determine the equatorial coordinates of radiants for non-basis meteor observations. The accuracy of determining the radiant coordinates has been estimated to be 4′–5′. Prospects for obtaining the kinematic characteristics of meteor particles are discussed.