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The last update of this file: May 18, 2015

Here you can read about poorly understood, or little known properties of meteoroidal meteors (with exception of electrophonic sounds) and on other related topics.
The author published several articles on the items in early 1990s. And it is time to consider them again.

There was some excitement when it was discovered that a thunderstorm was associated with the 'antimatter radiation':
http://www.nature.com/news/rogue-antimatter-found-in-thunderclouds-1.17526
Maybe the discovery is a clue to many puzzles of a thunderstorm? Or maybe it is beginning of a new intriguing puzzles? Who knows...

Many intriguing discoveries on thunderstorm radiation were done by such researchers as Sir Basil Schonland FRS (1896-1972)
http://en.wikipedia.org/wiki/Basil_Schonland
as long ago as in 1920s and the early 1930s, but they were quickly forgotten...

After death of Konstantinov in 1969 the idea of the 'antimatter meteors' was quickly forgotten.

But forgotten also were the intriguing experimental results... Indeed how to explain them?

It looks like nowadays when the 'antimatter thunderstorm' appears, it is a proper time to reconsider the old meteor's results again. Meteor phenomena produce many puzzles. Who knows, maybe future 'nuclear meteor' research help to better understand some meteor's mysteries as electrophonic sounds, reported electric disturbances, etc.?... Just future can say...

http://adslabs.org/adsabs/abs/1966CosRe...4...58K/

http://adslabs.org/adsabs/abs/1971wssp.conf...82K/

http://adslabs.org/adsabs/abs/1971sp1..conf...82K/

http://adslabs.org/adsabs/abs/1970KosIs...8..931K/

http://adslabs.org/adsabs/abs/1969IzSSR..33.1820K/

Some of other meteor's puzzles are discussed in my article/paper: "Probable Role of Plasma Instabilities in Anomalous High Altitude Luminosity Observed in Meteors and Space-Vehicles Re-entries" AIAA Paper 2000 - 0589, 9pages.

The problem of meteoroid's flights is an interdisciplinary one, involving many branches of science. Despite significant progress in understanding the physics of meteor phenomena, several aspects are still not well understood. Among them, there are problems of origin of the so-called head echo; luminous meteor trails of very long persistence; and visibility of meteors at anomalously high altitude. In this paper the latter problem is considered. It concerns luminosity of meteors at heights above about 120 km. The author ( here and below the author means A. Ol'khovatov, unless otherwise stated ) published several articles on the subject in the early 1990s. Since that time new data have appeared which confirm the general ideas previously put forward.

Meteor data. It has been generally accepted that meteors initially appear a little bit higher than 100 km height, usually no more than about 110-115 km. But in the last couple of years several reports have appeared describing anomalously high altitudes of some meteors. For example, Y. Fujiwara and colleagues[1] discovered beginning heights of two Leonid moderate fireballs of 160 km. During the Dutch Leonid meteor expedition to China in 1998, beginning heights of luminous trajectories of bright Leonids were observed up to 200 km by an all-sky video system [2,3]. Dr. Z. Ceplecha wrote [3] to the author that the nature of the high-velocity high-altitude meteor-radiation is an enigma. With hundred meters of free mean path for atmospheric gases, classical ablation (mass-loss) processes are excluded. Excitation of the air molecules in sufficient degree to explain the radiation through impacts on meteoroid surfaces seems to be excluded, too, in Ceplecha's opinion.
In reality, the phenomenon of anomalous high altitude luminosity (AHAL) of meteors has been known for at least several decades. In the late 1940s Soviet astronomer I. Astapovich saw in Crimea during some nights what he called "blue meteor trails" at heights up to 160 km. A remarkable meteor spectrum was recorded in 1970 [4]. At first, at 137 km height yellow-red continuum appeared, which was ascribed [4] to the first positive group of nitrogen bands. Down to 116 km the level of brightness was about constant. At 116 km it brightened rapidly from its previous level into a uniform continuum. At 106 km the D-line of neutral sodium appeared and at 105 km all other lines of the typical meteor spectrum also appeared. The continuum remained dominant to 87 km, were the meteor ended abruptly. The meteor speed was about 18.5 km/s and its magnitude (luminosity) was about zero.
There are other reports on meteors with unusually strong nitrogen emissions. For example, a recording of 2 meteors within 2.5 hours with especially strong nitrogen bands, which "may indicate an abnormal atmospheric condition at the time"[5].
It is important to note that 2 MHz radars detect meteors up to 140 km height[6].

Space-vehicle re-entry data. Although not widely known, glow phenomena associated with space-vehicle re-entries, which cannot be explained as glow of re-entry plasma, were investigated in USSR in the early 1960s [7]. They were discovered by A. Lazarev and N. Uspenskii in 1960 during a night experiment with a re-entry vehicle. On July 6, 1960 a radiometer ( wavelengths 1.8-3.2 microns, i.e. infrared ) installed on the re-entry vehicle registered an upsurge of brightness commencing at 160 km height with maximum at 125 km. The level of the brightness was pulsating. Then the brightness dropped sharply and began to increase again from about 100 km to 85 km, where radio transmission "blacked out" due to re-entry plasma. In another experiment on July 24, 1962 on a re-entry vehicle there were several radiometers working in 0.8-3.2 micron band. During the approach to Earth at heights 145-105 km the radiometers were saturated with a strong signal. Then, at lower heights, the signal dropped to a minimum at 90 km, and later raised again.
It is well known that the re-entry plasma forms at heights below about 100-80 km (about 80 km for re-entry of SOYUZ-sized space vehicles, and about 100 km for large Space Shuttle). The radiometers detected the re-entry plasma signal. But what was the source of the "120 km" signal? Investigations conducted at the time were unable to find a comprehensive explanation. So the results were taken with some suspicion until they were confirmed during manned space vehicle re-entries[7]. On April 25, 1971 there was a night re-entry of SOYUZ-10 spaceship. During the re-entry phase the crew was looking through windows. About 2-3 minutes after the reentry vehicle separation from its main body, a weak whitish-violet glow was seen through the windows. The glow gradually increased in brightness. Sometime later a small deceleration was felt, as small particles suspended in the air began to move to the vehicle floor. The glow brightness continued to increase, achieving the earth's daylight sky level. The impression was that the vehicle had gotten out of the earth shadow and flew over its daylight side. The glow was uniform. After the vehicle reached a height about 80 km, the violet color of the glow changed to white, the glow began to pulsate, and pink strips appeared in the glow. Soon it began to resemble a campfire by its red color and pulsating strips.
After the SOYUZ-10 data, Soviet scientists realized that the 1960s results were correct, that there was indeed a real unexplained glow with maximum at about 120 km. It was again confirmed by the crew of SOYUZ-23 spaceship during a night re-entry on October 16, 1976. Light inside the re-entry vehicle was switched on. The glow was first noticed by the crew when their re-entry vehicle was at 120 km height. At that time the glow was in a form of flashes with frequency about 1 per second. Then the duration of the flashes and repetition rate increased and the glow transformed into a continuous one. It resembled a white fog and lasted for rather long time. Below about 100 km a reddish re-entry plasma glow was added. The latter glow was very different from the previous one.

So we can state the reality of the AHAL for meteors and for space-vehicle re-entries. But the question arises: what is a physical mechanism of the luminosity?
Regarding the space-vehicle re-entries, one proposed explanation was that it was non-equilibrium ionospheric glow excited by space vehicle flight. Among proposed origins (put forward by L. Grechikhin, S. Avakyan and others) were collisions with atmospheric molecules, photoelectrons due to solar flares, electric discharges due to electrification of the space vehicle [7]. Richard Spalding[8] interprets the observed AHAL of meteors to be explainable as due to ions from the ionosphere being (electrostatically) attracted to the incoming body and colliding with it to produce the light.
Regarding the author's opinion, at first, it would be reasonable to note that Leonids meteoroid ram surface is heated up several hundreds degrees due to gasdynamic drag at 160 km height. And due to the loose, fragile structure of Leonids, their behavior is hard to predict already at this large height. Moreover, it would be reasonable to note, that atmospheric density can increase as much as 60% during high solar activity at 160 km height, and to 130% at 200 km height. Atmospheric gravity waves also can alter the density up to a few dozen percent. This can shift the "meteor height scale" upward by 20-30 km at these heights.
Anyway, as it has been demonstrated above, besides Leonids, there are other examples of AHAL phenomenon, which can't be explain by these ways. There are several reasons why the author is inclined to think that plasma instabilities play major, or at least, significant role in the AHAL. Those arguments will be explained below.

Luminous efficiency. Despite the above-mentioned problems with analysis of Leonids, let's begin with them, as the most well-known example of AHAL. Let's consider the Leonid meteoroid moving at 71 km/s, which has produced the meteor with visual magnitude about -4 when entering the dense atmosphere[1]. Unfortunately, it is hard to estimate the luminosity of the Leonids at 160 km[1] due to a lack of data. If to accept[1] that the threshold magnitude for TV camera observation is normally about +7, then the corresponding luminosity in visible spectrum is on the order of several watts. Let's compare that with the meteoroid's gasdynamic drag power. The latter for the above-mentioned Leonid meteoroid can be estimated as on the order of a hundred watts. It means that a ratio of transformation of kinetic energy into visible luminosity (i.e. so called "luminous efficiency") is on the order of several percent at least. By comparison, luminous efficiency in the dense atmosphere (about 100 km and below) for a similar sized Leonid is considered to be an order of magnitude less[9]. But a difference in spectral sensitivity of TV-camera and photo-film possibly can explain the difference. So if the estimations above are correct, it means that either the high altitude "single collisions" mechanism of luminosity is, at least, as effective as the "continuum flow" mechanism at lower heights, or that there are other mechanisms. The first idea looks unlikely, but due to uncertainty of data a final conclusion regarding Leonids can't be done.
The other than Leonids AHAL events points to the other mechanisms.

In general, there can be two types of possible AHAL mechanisms. The first one is associated with a conversion of meteoroid's kinetic energy into the luminosity. In the second one the luminosity energy is supplied from the ionosphere. Let's begin with the first one.

Ion beam instabilities. At the 160 km height the mean free path of the ambient neutrals is dozens of meters. So the meteoroid is moving in free stream flowfield. Ambient neutrals striking the meteoroid can transform some part of their kinetic energy into excitation and ionization, as the ionization level of ambient neutrals corresponds to meteoroid's speeds about 10-15 km/s. For example, it is thought[9] that about 30% of oxygen atoms striking a meteoroid at 60 km/s are ionized. Then the neutrals and ionized components are "sprayed" from the meteoroid's surface, and their speed relative to the ambient ionosphere is approximately the meteoroid speed. In other words, there is a beam of ions moving through the ionospheric plasma with a meteoroid's velocity. Such ion beam is exposed to many types of plasma instabilities, leading to generation of plasma waves, heating up electrons etc. Here the author will call them simply the "ion beam instabilities", to prevent going into detailed considerations.
The instabilities can lead to the Alfven critical ionization[10]. In its typical scenario, neutrals as well as newly created ions are travelling across the geomagnetic field. The ions slow down as they transfer kinetic energy to the electrons via plasma waves. It is thought[10] that the main role is played by electrostatic plasma waves, due to lower hybrid and/or modified two stream instabilities. They heat up electrons in the plasma and ionize the neutrals. The ionization occurs when kinetic energy of the neutrals is equal to their ionization potential[10]. The critical speed is 10.6 km/s for molecular nitrogen and 15.6 km/s for atomic oxygen. To excite luminosity even slower speed is enough. As we saw, the speed of neutrals and ions repelled by the meteoroid can be much higher. Unfortunately, applications of the critical ionization velocity mechanism for ionospheric environment have not been investigated enough. Experiments with injections from space vehicles give ambiguous results, so maybe the mechanism is not very effective in these cases[10]. On the other side, the speed of a meteoroid is much higher than that of space-vehicles, and it can make the critical ionization mechanism more effective.

Luminous meteor trails. The problem of a long-living luminous meteor trails is not completely resolved. In the author's opinion, besides chemiluminiscent reactions, excitation by electrons due to plasma instabilities may play an important role[18]. It seems that experiments[19] with injection of high-speed plasma into the lower ionosphere support the idea. They revealed that the high-speed plasma injection can lead to formation of a large luminous area in the ionosphere, which continues to glow up to 3 minutes, despite that it contains practically pure air. It is important to add here, that sometimes cosmonauts see the "whole atmosphere glow" phenomenon, which in the author's opinion can be favorable to AHAL, and to the appearance of long-living luminous meteor trails[15].
A good confirmation that at least sometimes luminous meteor trails can be produced by plasma instabilities is an observation of a "jet of luminosity" produced by meteor in electrified ionospheric D-region[20].
Another interesting phenomenon, which in the author's opinion is an analog of meteor luminous trail[18] formed by plasma instabilities, has been seen during a Space Shuttle re-entry[21].

Head echo. An unresolved problem of meteor physics is the meteor head echo[22], i.e. a radar target moving with a meteor velocity. The author has proposed that a head echo is caused by generation of plasma waves in surrounding ionospheric plasma and in meteor's ablation products[23]. The ion beam instability could be a one of sources of the plasma waves, as at the head echo heights a density of ions "sprayed and repelled" by a meteoroid is rather high, and moreover, the ions are not trapped by geomagnetic field. Also maybe some coupling with the magnetoionospheric waves is important also, as the waves are associated with ionospheric irregularities. Evidently much more must be done to investigate details.
This interpretation of a head echo predicts some shift between a meteoroid velocity calculated from its trajectory, and from its Doppler radar return, due to the plasma waves[23]. And it seems that the prediction are being confirmed. Radar data indicate some difference between these two velocities[22].

Power events. Very bright bolides are rare events. But some ideas about ionospheric process, associated with them can be obtained through examination of large rocket launches. For example, during the Aug.30, 1983 night launch of Space Shuttle, the main engines themselves were making a much brighter orange flame than expected[24]. It was pulsating almost as if an engine was running unstable, but all the engines were okay[24]. In the author's opinion, the pulsation was caused by plasma instabilities in a shock wave around the engine exhaust at about 100 km height. A re-entry of the Shuttle was accompanied by the above-mentioned luminous phenomenon in its wake 6 days later[21].
The plasma instability factor also can explain some anomalous effects associated with Saturn rocket launches in 1960s. During some launches an anomalous noise-like fluctuation and attenuation affecting radio transmission occurred as the rocket under power from liquid-hydrogen liquid-oxygen engine passed through certain altitude regions between 100 and 250 km[25]. An idea was put forward[25] that the effects were caused by an interaction of the engine exhaust with the ionosphere. But attempts to calculate the effects have failed[25]. Here the author would like to say the following. The irregular character of the effects hints on the unstable ionosphere plasma role. Moreover, low-latitude ionospheric irregularities are registered the most often at these altitude regions. And indeed, published ionospheric sounding data[26] during one of the launches reveals appearances of spread F, and sporadic E layer at some distance from the rocket trajectory a few minutes after the launch. It hints they could be caused by the magnetoionospheric waves, generated by the launch. The author's evaluation has shown that the type of spread F irregularities can be responsible for the observed effects[15]. It is interesting also to mention a luminosity associated with exhaust plume of Apollo 8 spacecraft[27]. Maybe it was caused by the plasma effects, and not by solar scattering[15]?

Geophysical meteors. In many of the above-mentioned events, a meteoroid (or a space-vehicle) was just a trigger of ionospheric plasma instabilities. But sometimes there may be no need for a meteoroid to act as a trigger. Meteor-like phenomena can be produced by ionospheric plasma processes without a meteoroid as a trigger. Mechanisms of such strong self-organization of ionospheric plasma are not clear. As expected, these geophysical meteors are the most often in an auroral zone, where plasma normally is in an unstable state. There they are called "auroral meteors"[28].
In another case, a huge fireball explosion of non-meteoroidal origin was registered by a Soviet cosmonaut on May 5, 1981. It is quite remarkable that similar phenomena are registered in the lower atmosphere also[29-31], where there is no "classic" plasma. The latter events are the hardest to explain.

As we can see, plasma effects can play a large role in meteor phenomena. Especially important are the effects in the case of unstable conditions of ionospheric plasma. In the latter case resulting phenomena are difficult to foresee. Currently, our knowledge of plasma processes is not good enough for such predictions. Nevertheless, the author hopes that this work will attract attention of experts in meteors, and in plasma physics, and will help foster cooperation between them.

1. Fujiwara Y., Ueda M., Shiba Y., Sugimoto M., Kinoshita M., Shimoda C. (1998): "Meteor luminosity at 160 km altitude from TV observations for bright Leonid meteors" // Geophysical Research Letters, vol.25, p. 285-288.
2. Spurny P., and Betlem H. (1999): "Leonids - first results from the ground-based expedition to China", Leonid MAC Workshop, NASA AMES Research Center, Moffett Field, CA, USA, April 12-14.
3. Ceplecha Zdenek, Astronomical Institute of Czech Republic (1999), personal communication.
4. Cook A.F., C.L. Hemenway, Millman P.M., Swider A. (1973): "An unusual meteor spectrum", Evolutionary and Physical Properties of Meteoroids. ed. by Hemenway L., Millman P., and Cook A., NASA, SP-319, pp.153-159.
5. Barbon R., Russel J.A. (1968): "Some unusual spectra of meteors from the Palomar 18-inch Schmidt file", Physics and Dynamics of Meteors, ed. by Kresak L., and Millman P. M., Dordrecht-Holland, pp.119-127.
6. Olsson-Steel D., Elford W.G. (1987): "The height distribution of radio meteors: Observations at 2 MHz" // Journ. Atmos. Terr. Phys., v.49 No.3, pp.243-258.
7. Lazarev A.I. (1997): "Svechenie vokrug kosmicheskikh apparatov" // Opticheskii zhurnal, v.64, No.10, p.109-114 (in Russian).
8. Spalding Richard, Sandia National Laboratory, USA (1999), Personal communication.
9. Bronsten V.A (1981): Fizika meteornykh yavlenii. Nauka, Moscow, 416 p. (in Russian).
10. Hastings D.E. (1995): "A review of plasma interactions with spacecraft in Low Earth orbit" // Journ. Geophys. Res., v.100, No.A8, pp.14457-14483.
11. Milineskii G.P., Romanovskii Yu.A., Yevtushevskii A.M., Savchenko V.A., Alpatov V.V., Gurvich A.V., and Lifshits A.I. (1990): "Opticheskie nablyudeniya v aktivnykh eksperimentakh po issledovaniyu verkhnei atmosfery i ionosfery Zemli" // Kosmicheskie issledovaniya, vol.28, issue 3, pp.418-429 (in Russian).
12. Ol'khovatov A.Yu. (1992): "Magnetoionospheric wave perturbations and their correlations with various natural phenomena" // Izvestiya, Earth Physics, vol.28, No.10, pp.918-921.
13. Gurta S.P. (1988): "Expansion of plasma in the wake region of moving rockets - evidence of enhanced electron temperature" // Adv. Space Res., vol.8, No.1, pp.225-228.
14. Morse F.A., Edgar B.C., Koons H.C., Rice C.J., Heikkila W.J., Hoffman J.H., Tinsley B.A., Winningham J.D., Christensen A.B., Woodman R.F., Pomalaza J., and Teixeira N.R. (1974): "Equion, an equatorial ionospheric irregularity experiment" // Journ. Geophys. Res., vol.82, No.4, pp.578-592.
15. Ol'khovatov A.Yu. (1994): "Plazmennye neustoichivosti i kosmicheskie apparaty" // Priroda, No.8, pp.48-55 (in Russian).
16. Ol'khovatov A.Yu. (1990): "O roli nadteplovykh electronov v obrazovanii svetyaschikhsya oblastei v okrestnosti kosmicheskogo tela" //Geomagnetizm i Aeronomiya, vol.30, No.1, pp.161-163 (in Russian).
17. Chapin E., Kudeki E. (1994): "Plasma wave excitation on meteor trails in the equatorial electrojet" // Geophys. Res. Lett., vol.21, No.22, pp.2433-2436.
18. Ol'khovatov A.Yu. (1990): "K voprosu o svechenii meteornykh sledov" // Geomagnetizm i Aeronomiya, vol.30, No.5, pp.844-846 (in Russian).
19. Adushkin V.V., Zetser Yu.I., Kiselev Yu.N., Nemchinov I.V., Khristoforov B.D. (1993): "Aktivnye geofizicheskie raketnye eksperimenty s injektsyei vysokoskorostnoi plazmennoi strui" // Doklady Akademii Nauk (Russia), vol.331, No.4, pp.486-489 (in Russian).
20. Strabley R., Suszcynsky D.M., Roussel-Dupre R., Symbalisty E.M., Armstrong R.A., Lyons, W.A., Nelson T.A. (1998): "Video and Photometric Observations of a Possible Meteor-Triggered Sprite/Jet Event" // Abstract presented at the Amer. Geophys. Union 1998 Fall Meeting.
21. Anonymous (1983): "Shuttle mission 8 astronauts photograph reentry phenomena" // Aviation Week and Space Technology, vol.119, No.12, pp.20-21.
22. Pellinen-Wannberg A., Westman A., Wannberg G., Kaila K. (1998): "Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data" // Annales Geophysicae, vol.16, No.11, pp.1477-1485.
23. Ol'khovatov A.Yu. (1991): "K voprosu o golovnom ekho meteorov" // Geomagnetizm i Aeronomiya, vol.31, No.4, pp.750-751 (in Russian).
24. Covault C. (1983): "Shuttle Launch Verifies Thrust Margins" // Aviation Week and Space Technology, vol.119, No.10, pp.21-23.
25. Baghdady E.P., Ely O.P. (1966): "Exhaust plasma transmissions effects" // Proc. IEEE, vol.54, No.9, pp.1134-1146.
26. Felker J.K., Roberts W.T. (1966): "Ionospheric Rarefaction Following Rocket Transit" // Journ. Geophys. Res., vol.71, No.19, pp.4692-4694.
27. Kung R.T., Cianciolo L., Myer J.A. (1975): "Solar Scattering From Condensation in Appolo Translunar Injection Plume" // AIAA Journ., vol.13, No.4, pp. 432-437.
28. Corliss W.R. (1983): Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena. The Sourcebook Project, Glen Arm, MD, 242 p.
29. Docobo J.A., Spalding R.E., Ceplecha Z., Diaz-Fierros F., Tamazian V., Onda Y. (1998): "Investigation of a bright flying object over northwest Spain, 1994 January 18" // Meteoritics & Planetary Science, vol.33, No.1, pp.57-64.
30. Morss D.A. (1998): "SPARKE (Spherical Propagating Atmospheric Radiative Kinetic Emission): Fireball in the Sky?" // Abstract presented at Amer. Geophys. Union 1998 Fall Meeting.
31. Ol'khovatov A.Yu. (1999): "Evidences for geophysical origin of the 1997 Greenland fireball event" // Proc. 6th Intern. Symp. on Ball Lightning, Aug.23-25, 1999, Univ. of Antwerp, Antwerp, Belgium, ed. G. Dijkhuis, pp.38-41 (also posted at: www.geocities.com/CapeCanaveral/Cockpit/3240/gr1997.htm).

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