Meteor Observations Research Articles

Observations of Meteors using an over-the-horizon Radar

AbstractWhen metre wavelength radars were first operated in the 1940s, echoes were obtained which could be attributed to backscatter from ionised trains produced by the ablation of meteroids in the upper atmosphere at altitudes near 100 km. Modern over-the-horizon skywave radars operating in the HF (High Frequency) band employ digital techniques for both radar control and signal processing and are aided by frequency management subsystems for the selection of appropriate frequencies for meteor detection based on real-time monitoring of the HF signal environment.This paper describes the results of using such a radar for meteor observations. We report the detection of the Eta Aquarid meteor shower and demonstrate that a large increase in the echo rate due to sporadic meteors is obtained as frequencies are reduced below 15 MHz and the underdense echo ceiling rises in altitude. Finally, we present preliminary observations of highly Doppler shifted echoes which travel at meteoric velocities and which we identify as meteor ‘head echoes’.

Meteor astronomy: A mature science?

In this article we attempt to trace the development of contemporary meteor science from C. 1830 to C. 1960. From its new beginnings in the early 1830's, the subject saw its most dramatic growth and development in those years surrounding the turn of the 19th century. While the period between C. 1910 to C. 1930 saw a decline in its greater interest, the period between C. 1920 to C. 1950 saw the science enter a stage of consolidation. Around the mid 1950's a stand-off between the theory of meteor ablation and observations arose forcing a re-evaluation of the meteoroid model. These recent developments in meteor studies would suggest that the science is mature in the sense described by Thomas Kuhn.

Meteor Studies

Historically meteor astronomy is one area where amateurs have always been able to make significant contributions. In fact, in the 19th century, it was amateur naked eye and telescopic observations which laid down much of the foundations of meteor astronomy. References to this work can be found in any textbook on meteors. The 19th century observers concentrated on counting meteors, estimating magnitudes and plotting the meteor paths on star maps. Their main interest was to determine hourly rates and shower radiants. An important milestone was Denning’s radiant catalogue (Denning 1882), which included 4367 shower radiants. Although it is now believed that many of these radiants are spurious, the catalogue is still a useful reference. Unfortunately Denning and other 19th century observers often combined sporadic meteors observed on different nights into a minor stream radiant. This habit of “radiant hunting” is even today quite popular among some amateur observers. However, in all fairness it should be emphasized that most of the 20th century amateur meteor observers applied very strict criteria to their radiant determinations. Names such as J.M. Prentice in Great Britain, R.A. McIntosh in New Zealand and R. Rigollet in France may be mentioned.

Observations of Comets, Minor Planets and Meteors in Japan

In the early period of this century, some comets were discovered by Japanese amateur astronomers. Just fifty years ago, in 1937, Minoru Honda began to search for systematically comets with his 15-cm reflector. He observed Comet Encke without an ephemeris in November, 1937, and made his firts discovery of a comet in 1940. This comet was also discovered independently by Shigeki Okabayashi (Comet Okabayashi-Honda, 1940e). Subsequently, Honda discovered Comet Friend-Reese-Honda (1941a) in 1941. Unfortunately, Okabayashi was killed at the Second World War in 1945.After the end of the war, Honda discovered ten comets during 1947 and 1968. In 1968, he discovered three comets in a year. He has been an active observer of comets and novae. Stimulated by Honda’s success, Tsutomu Seki began his comet hunting in 1950, and his long and patient efforts were rewarded with the discovery of Comet Seki, 1961f. Seki later discovered six comets, and rediscovered six short-period comets before 1981. In that year, Seizo Goto, a well-known telescope maker in Japan, donated a 60-cm reflector. Since then, with the Goto telescope, Seki has made many astronomic observations of comets and minor planets. He has rediscovered some periodic comets and has discovered many minor planets every year.

Debris from comet Halley, comet's mass loss and age

Large particles released from the nucleus of comet Halley, but undetected directly by space probes, seem to affect decisively the mass loss and mass determination of the comet, and consequently its aging. Simultaneous radar meteor observations in 1985–86 at the approaches of the comet emphasize the relatively larger proportion of long-duration echoes with respect to previous years.

Radar observations of the Lyrid meteor shower at Budrio

Radar meteor observations carried out at Budrio (Italy) during the Lyrid meteor shower period in 1983–1985 are analysed and discussed. Lyrid activity is obtained applying to the observations a range distribution method. The maximum of activity is found at solar longitude 31.3° (epoch 1950), the duration of the shower between quartermaximum points is about 2 days and the overall Lyrid activity approximately 6 days.

The First GLOBMET Symposium

The First GLOBMET Symposium was held in Dushanbe, Tadzhikistan, U.S.S.R., August 19–24, 1985. GLOBMET (Global Meteor Observation System) was first proposed by the Soviet Geophysical Committee in Moscow (specifically, by committee members B. L. Kashcheyev and V. A. Nechitailenko) and was accepted by the Middle Atmosphere Program (MAP) Steering Committee of the Scientific Committee on Solar‐Terrestrial Physics (SCOSTEP, part of the International Council of Scientific Unions) as a MAP project in 1982. While the atmospheric dynamics data from the system are of primary interest to MAP, GLOBMET also encompasses the astronomical radio and optical observations of meteoroids and the physics of their interaction with the earth's atmosphere.

Momentum flux variations at lower thermospheric levels as seen from mid-latitude meteor wind observations

Computations of momentum flux were made for the meteor wind data collected at Atlanta (34°N), during the period August 1974–March 1978. Substantial transport of momentum due to diurnal tide during summer and semidiurnal tide during winter was observed over the station. Monthly mean momentum flux variations of diurnal and semidiurnal tides exhibited oscillations with periods of about six and four months respectively. The height variations of annual mean momentum flux due to diurnal and semidiurnal tides revealed poleward flux throughout the height region 82–98 km and severe damping of momentum flux due to diurnal tide between the heights 90 and 92 km. The results of the present study relating to the northern hemisphere mid-latitude station are compared with those of Adelaide (35°S), the southern hemisphere mid-latitude station.

Observation of a possible optical burst of the double star Beta Camelopardalis

An intensified SEC Vidicon observation of a brightening of the image of Beta Cam for a duration of about 0.25 sec at 0932 UT on December 4, 1969 is described. The observation was made during airborne observations of meteors over Canada between latitudes of 50 and 60 deg N.

The flux of meteoroids in the vicinity of the orbit of Comet Halley

On the basis of simultaneous observations of the Orionid meteor shower in Italy and Czechoslovakia during the period 1978–1982 the flux densities of meteor particles in the near-perihelion distances have been derived and related to previous results of observations of the shower associated with Comet Halley. A maximum flux rate of 2·10−10 m−2 s−1 has been obtained for the particles of the mass range higher than 10−6 kg at the distances of (0.09÷0.005) A.U. from the orbit of the comet. The flux in the most inner core of the stream, relative to the particles of the mass range lower than 10−6 kg, is controlled by the fresh cometary ejecta and hence depends on the mass-loss rate of the of the comet and on its gas/dust relation. The meteor shower observations yield a mass loss rate of solid particles of 3.3·1011kg/revolution. Ths value increases the hazard of the space experiments by more than 1 order of magnitude.

Three-station meteor wind observations in Northern Europe during summer 1980

During the summer of 1980 meteor wind data were recorded simultaneously at Bologna (44.5°N), Sheffield (53.5°N) and Stornoway (58.2°N). Hour by hour comparison of tides and planetary waves in the meteor region shows that their mean behaviour is well resolved and permits the determination of wave numbers as well as meridional structure. Systematic differences exist in the amplitudes and phases recorded at the different latitudes which may reflect local variations in the stratospheric wind and temperature fields.

Two-station television observations of Perseid meteors

Two-station television observations of Perseid meteors

A fireball in Jupiter's atmosphere

One fireball was photographed during two encounters with Jupiter. Its total luminosity was 1.2 × 105 0 mag s (at standard range 100 km). If we employ the luminous efficiency proposed by Cook et al. (1981) for slip flow of a meteoroid in its own vapors we obtain an estimated mass of 11 kg. A rough absolute magnitude is −12.5. If we note that we searched for a total of 223 s during two exposures, we estimate a number density near Jupiter of 7 × 10−28 cm−3 for masses of meteoroids of 3 kg and greater. This value is about a factor of 6 smaller than a rough upper limit reached from an extrapolation from terrestrial observations of meteors and comets.

Seasonal variation in mesospheric semi-diurnal tides. Comparison of meteor radar observations and results from an excitation source model

The seasonal variation of the semi-diurnal tide is well established in the upper mesosphere from meteor radar observations, such as those made at Garchy (France). A classical propagation model, using a realistic excitation source from ozone and water vapour solar heating, can account for most of the seasonal variation characteristics, and in particular the strong difference between summer and winter features.

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

In this final of three papers from the NASA-NMSU Meteor Observatory, trajectory and orbital elements are reported for 13 doubly-photographed meteors, four of which are Geminids and one an Orionid. A pair of meteors with rather similar orbits suggests the possibility of a new stream active in the range of solar longitude 200 deg to 204 deg (13-18 October) with a radiant near delta Aurigae.

Dynamics of Micrometeoroids

Recent observations of zodiacal light have established a reliable and consistent picture of the spatial distribution of interplanetary dust in the ecliptic plane. The spatial density nr varies with heliocentric distance r according to a power law nr ∝ r−ν. From Helios observations an exponent v = 1.3 is derived for the distance interval from 0.08 A.U. to 1 A.U. (Link et al. 1976). Outside the earth's orbit the Pioneer 10 and 11 results suggest a higher exponent v = 1.5 for the distance interval from 1 A.U. to 3.3. A.U. (Hanner et al., 1976). Giese and Grün (1976) showed that the results from zodiacal light observations are compatible with the micrometeoroid fluxes derived from in situ measurements and lunar crater statistics. They found that micrometeoroids in the size range from 10 μm to 100 μm radii (corresponding roughly to 10−8g to 10−5g) contribute most to the zodiacal light brightness.The orbital distribution of large interplanetary particles (10−6 g < m < 10−3g) is known from meteor observations. Sekanina and Southworth (1975) reported average orbital elements of these particles: ā ∼ 1.25 A.U., ē ∼ 0.4 and ī ∼ 20°. Orbital information on micrometeoroids (m < 10−8g) is obtained from in situ detectors on board the Pioneer 8 and 9 and Helios 1 spaceprobes and the HEOS-2 satellite. Characteristics of the different micrometeoroid experiments are given in Table 1. There is almost no time overlap in the data taking intervals of the experiments. Therefore one has to assume that there are no time variations of the meteoroid flux on the time scale of 1 to 10 years if one compares the results from the different experiments. This assumption may be violated for the smallest of the observed particles (m < 10−13g) due to strong electromagnetic interaction of these particles with the interplanetary magnetic field (Morfill and Grün 1979).

Observations of lower ionospheric wind by the Kyoto Meteor Radar

This paper describes the results of meteor radar observations which have been carried out at Kyoto University since December 1977. The radar, a coherent pulse Doppler radar with transmitting frequency of 31.57 MHz and nominal peak power of 10 kW, measures wind fields at meteor heights of 80–110 km. The solar semidiurnal tide generally dominates the wind oscillations at these heights. The less regular diurnal tide has comparable magnitude. The variability of the tidal structure suggests the possibility of interaction between respective waves or winds, particularly the influence of disturbed conditions in the lower atmosphere. Other components of winds as mean flow or a quasi 2‐day planetary wave have also been observed. The combination of meteor wind radar and other observational techniques will further the understanding of the global dynamics of atmospheric waves.

Television observations of Perseid meteors

Television observations of Perseid meteors

The applications of radio-wave scattering theory to radio-meteor observations

The observation of radio meteors is an important technique providing information on the neutral atmosphere in the height range 80–110 km. Reliable interpretations of such observations require a knowledge of the process of radio-wave reflection from meteoric ionization. It is shown that recent theoretical results modify the interpretations based on approximate scattering models whose use may result in serious errors in the values of such parameters as ambipolar diffusion coefficients, diffusion scale heights, neutral atmosphere wind velocities and associated wind shears.

Meteor winds over Sheffield (53°N, 2°W)

The development of the Sheffield meteor radar to its present state is described and the results of two ‘special’ periods of wind observations, in August 1974 and in January 1976, are presented. The data show marked differences between the summer and the winter sets particularly with respect to oscillations in the wind whose periods exceed one day. Individually the two sets agree well with the seasonal means established during 12 years' meteor wind observations at Sheffield.