Meteor Heights Research Articles

IMPROVING THE USE OF GEODETIC, GEOCENTRIC, AND TOPOCENTRIC COORDINATE SYSTEMS IN METEOR ASTRONOMY AND RELATED TASKS

The problem of using the geodetic, geocentric, and topocentric coordinate systems in video observations’ processing of meteors and other dynamical objects in Earth’s atmosphere is considered. For meteor heights in a range of 0…200 km and arbitrary Earth’s ellipsoid latitudes, the following values are calculated: the difference between geodetic and geocentric latitudes, the meridian arc length corresponding to this shift, and the difference between geocentric and geodetic altitudes above the Earth’s ellipsoid. The carried-out calculations allowed us to conclude that the geocentric coordinate system is optimal for the calcula- tion of kinematic parameters of meteors and trajectory measurements of ballistic objects at all-range altitudes and long distances between observation points without using horizontal coordinate systems as intermediate ones. This coordinate system is also used in the computation of heliocentric orbit elements of meteoroids. It is noted that the transition from the geocentric to the geodetic coordinate system is necessary for mapping the projections of the meteor trajectory to search for their remnants — meteorites. The reason is related to the difference between them, which can reach 11 arcmin for objects located at an altitude of 100 km above the level of the Earth’s ellipsoid, which corresponds to the shift of 21 km. The difference between geocentric and geodetic altitudes is inessential and amounts to half a meter at an altitude of 100 km and slightly more than one meter at 200 km and can be neglected in meteor calculations and most ballistic tasks. These considerations formed the basis for our proposed alternative vector method for the inverse transition from geocentric to geodetic coordinates and the numerical solution of the corresponding equation. In order to decrease the calculation time for mass processing, it is recommended to change the numerical processing of the inverse task by fitting it with elementary functions. An example of fitting is given. It brings to the maximal deviation in latitude near one arcmin, which corresponds to approximately 35 meters. It is noted that such precision is satisfactory for meteor measurements, but for ballistic problems, the accuracy of fitting must be improved.

On the origin of the Southern Delta Aquariids meteor shower

We determine the begin and end heights of meteors to calculate and compare the median kB parameter (Ceplecha, 1967) of several meteor showers observed throughout 2013. This parameter gives an indication on the type of parent body from which meteor showers originate. We propose that the meteoroids giving rise to the Southern Delta Aquariids consist of high strength material, likely asteroidal, unlike most meteor showers. In particular their parent body could be a C-type asteroid. We discuss the potential candidates in the light of existing literature and conclude that it could be a combination of comet 96P and asteroid 2003 EH1, with a higher relative abundance of the asteroid. The following results are obtained using observations from CILBO, a double station meteor camera set-up in the Canary Islands. Meteors are detected with MetRec, a meteor detection software (Molau, 1999) and the characteristics of their trajectories are computed using the Meteor Orbit and Trajectory Software (Koschny and Rio, 2002).

τ Herculid meteor shower in the night of 30/31 May 2022 and the meteoroid properties

Context. A τ Herculid meteor outburst or even storm was predicted to occur by several models around 5 UT on 31 May 2022 as a consequence of the break-up of comet 73P/Schwassmann-Wachmann 3 in 1995. The multi-instrument and multi-station experiment was carried out within the Czech Republic to cover possible earlier activity of the shower between 21 and 1 UT on 30/31 May. Aims. We report meteor shower activity that occurred before the main peak and provide a comparison with the dynamical simulations of the stream evolution. The physical properties of the meteoroids are also studied. Methods. Multi-station observations using video and photographic cameras were used to calculate the atmospheric trajectories and heliocentric orbits of the meteors. Their arrival times were used to determine the shower activity profile. The physical properties of the meteoroids were evaluated using various criteria based on meteor heights. The evolution of the spectra of three meteors were studied as well. Results. This annual but poor meteor shower was active for the whole night many hours before the predicted peak. A comparison with dynamical models shows that a mix of older material ejected after 1900 and fresh particles originating from the 1995 comet fragmentation event was observed. The radiant positions of both groups of meteors were identified and were found to agree well with the simulated radiants. Meteoroids with masses between 10 mg and 10 kg were recorded. The mass distribution index was slightly higher than 2. The study of the physical properties shows that the τ Herculid meteoroids belong to the most fragile particles observed ever, especially among higher masses of meteoroids. The exceptionally bright bolide observed during the dawn represents a challenge for the dynamical simulations as it is necessary to explain how a half-metre body was transferred to the vicinity of the Earth at the same time as millimetre-sized particles.

Improved method of estimating temperatures at meteor peak heights

Abstract. For 2 decades, meteor radars have been routinely used to monitor atmospheric temperature around 90 km altitude. A common method, based on a temperature gradient model, is to use the height dependence of meteor decay time to obtain a height-averaged temperature in the peak meteor region. Traditionally this is done by fitting a linear regression model in the scattered plot of log⁡10(1/τ) and height, where τ is the half-amplitude decay time of the received signal. However, this method was found to be consistently biasing the slope estimate. The consequence of such a bias is that it produces a systematic offset in the estimated temperature, thus requiring calibration with other co-located measurements. The main reason for such a biasing effect is thought to be due to the failure of the classical regression model to take into account the measurement error in τ and the observed height. This is further complicated by the presence of various geophysical effects in the data, as well as observational limitation in the measuring instruments. To incorporate various error terms in the statistical model, an appropriate regression analysis for these data is the errors-in-variables model. An initial estimate of the slope parameter is obtained by assuming symmetric error variances in normalised height and log⁡10(1/τ). This solution is found to be a good prior estimate for the core of this bivariate distribution. Further improvement is achieved by defining density contours of this bivariate distribution and restricting the data selection process within higher contour levels. With this solution, meteor radar temperatures can be obtained independently without needing any external calibration procedure. When compared with co-located lidar measurements, the systematic offset in the estimated temperature is shown to have reduced to 5 % or better on average.

Interferometric calibration and the first elevation observations at EKB ISTP SB RAS radar at 10–12 MHz

The method for calibrating elevation measurements at EKB ISTP SB RAS radar obtained for the period 20/09/2019–18/11/2019 is presented. The calibration method is a modernization of the method for calibrating radar by meteor trails. The main difference of the method is the use of not a statistically processed FitACF data, but the full waveform of the signals scattered on the meteor trails. Using the full waveform makes it possible to more reliably distinguish meteor scattering from other possible scattered signal sources, and to determine meteor heights from the trail lifetime using the NRLMSIS-00 model. A comparison of the results with the results of E-layer calibration method shows a good agreement. The first examples of regular elevation observations at the EKB ISTP SB RAS radar are presented, and their preliminary interpretation is given.

Meteors with extreme beginning heights from observations with high-sensitivity super-isocon TV systems

ABSTRACT Meteors with extremely high altitudes are considered. Parameters of seven meteors having anomalous beginning heights recorded with highly sensitive super-Isocon TV systems are presented. One 1993 Perseid meteor, one 2001 sporadic meteor and five meteors from the 2002 Leonid storm had beginning heights in the range 135–145 km. The sporadic meteor is used to demonstrate the methods of data processing and observation precision results. The original TV meteor images, photometric calibration curves and meteor light curve are shown. Light curves are shown for the Leonid shower meteors as well. Based on the sporadic meteor and the 2002 Leonid shower meteor data, mass-loss curves were calculated as functions of height and time: the maximum rates of mass loss were 0.14 and 0.20 g s−1, respectively. Using the classic equation for partially isothermal stone particle heating, the detected beginning heights of most meteors considered (136–135 km) are shown to possibly be related to blowing the molten layer off from a meteoroid surface and most segments of the light curves (below 124 km) show intensive evaporation. For some Leonid meteors, appearing higher than 145–140 km, energy exchange of atmosphere molecules and atoms with the ‘cold’ meteoroid surface can also be assumed. Another possible explanation lies in the low melting temperature of 1500–1600 K for Leonid meteors.

Signatures of meteor showers and sporadics inferred from the height distribution of meteor echoes

The SKYiMET meteor radar is capable of measuring the height distribution of ionized meteor trails. Observations of the Sodankyla radar (67°N, 23°E) in 2008–2019 are analyzed. A method is applied, based on the median and quartiles of meteor heights, for distinguishing meteor showers from much more intense background sporadic meteors. Since the shower meteors are commonly less dense and enter the Earth’s atmosphere at a larger velocity, they produce ionization up to 3 ​km higher than sporadic meteors. This effect manifests itself in the form of narrow peaks that are clearly visible in the median and quartiles of the meteor height. Seven established showers with zenith hourly rate (ZHR) ​> ​12 were identified. In addition, using both the height parameters and the radiant distribution, a signature of a former meteor stream evolving into sporadic meteors is found. This additional sporadic inflow has an antihelion source and occurs in the January.

Latitudinal difference in meteor trail ionization heights and identification of meteor showers

The ionization heights of meteor trails are strongly dependent on local atmospheric conditions in the mesosphere and lower thermosphere (MLT)-region. We present here latitudinal difference in ionization heights of meteor trails at two distinct latitudes, Thumba (8.5∘N, 77∘E), India and Eureka (80∘N, 85.8∘W), Canada. There is a large seasonal variation in meteor count at high latitude as compared to low latitude. Similarly, there is a large variation in meteor trail ionization heights at high latitudes, but not at low latitudes. However, it noticed that the trail ionisation heights at low latitude are found to be about 2 km higher. The latitudinal differences are probably related to changes in electron line densities at local MLT-regions. The identification of meteoroid streams in the sporadic background is still a noteworthy problem to pursue. By considering ionisation heights of meteor trails as a simple but robust metric, we identified shower meteors from the background sporadic activity, as the ionization heights of shower meteors are different from the sporadic meteors. We apply this shower detection technique on long-term data set at two different latitudes and compared with existing shower calendars. By using the median height of meteor trails and their corresponding upper and lower quartiles (Uq and Lq) as a metric, we unambiguously identified all northern hemisphere showers with a zenithal hourly rate larger than 20, which are in good agreement with the known showers.

Ablation of small iron meteoroids–First results

A population of faint meteors with low velocities, and low beginning heights have been described by Borovička et al. (2005) and Campbell-Brown (2015). They have only iron lines in their spectra. Most of them have unusual light curves that can not be explained by classical single body ablation theory or by fragmentation models. We developed a model which considers iron meteoroids and three different processes of the ablation. The comparison of theoretical and observed meteor heights and light curves leads to the conclusions that (i) vaporization of the liquid from the surface of the meteoroid is too slow a process and it is not able to explain the majority of the observed meteors. (ii) Breakup of the liquid drop would not occur at all or occur at heights which are too low. (iii) The immediate removal of the liquid from the meteoroid's surface and fast release of its kinetic energy is the most probable process leading to the observed meteors. This scenario predicts similar heights, lenghts, and light curves as observed meteors.

Variations in meteor heights at 22.7°S during solar cycle 23

The meteor radar measurements obtained at Cachoeira Paulista (22.7°S), Brazil, have been used to study a possible relationship between meteor echo height variations and solar flux during solar cycle 23. A good concordance between the normalized values of the annual mean of the meteor peak heights and F10.7 solar radio flux and Mg_II solar indexes have been observed during declining phase of the solar cycle 23. After eliminating the solar activity influence, the annual mean of the meteor echo peak heights showed a linear decrease of 30m/year when Mg_II solar index is used and 38m/year when F10.7 solar radio flux is used. When the trend is eliminated the relationship between meteor peak heights and F10.7 solar flux indicate a trend of 672m/100sfu (sfu-solar flux unit). The meteor amplitude signals and the decay time drops after mid-2004, which may be attributed to the decreasing of the electron density in the meteor trails. The meteor echo peak height decrease has been interpreted as being caused by a reduction in air density in the upper atmosphere.

Meteor heights during the recent solar minimum

Abstract. Average meteor heights have been continuously observed using a SKiYMET VHF radar at Collm (51.3° N, 13.0° E) since late summer of 2004. Initially, the daily mean meteor height was about 89.4 km. Since that time, average meteor heights have decreased. This is consistent with earlier results on middle atmosphere temperature change from the literature and from earlier results of low-frequency reflection height changes measured at Kühlungsborn and Collm. During the recent solar minimum 2008/2009 the meteor heights further decreased. Linear fitting of a trend and a solar cycle to the heights reveals a linear decrease of about −56 m year−1 and a solar cycle effect of +450 m per 100 sfu. Assuming that meteor heights, on a long-term average, approximately refer to a level of constant pressure, this decrease can be converted to a mean middle atmosphere linear temperature decrease of −0.23 K year−1 and a solar cycle effect of +1.8 K per 100 sfu during the last decade, which is in the range of observed trends reported in the literature.

Variation of Meteor Heights and Solar-Cycle Activity

Photographic meteor observations of the Perseid meteoroid stream compiled from the IAU Meteor Data Center catalogue are analyzed from the viewpoint of possible long-term variation of meteor heights with the solar-cycle activity, which was previously reported from radio observations. The observed beginning and end-point heights of the Perseids, normalized for the geocentric velocity and the absolute photographic magnitude, do not show a variation consistent with the solar-cycle activity. This result is valid for the mass range of larger meteoroids observed by photographic techniques, and must be still verified also for the range of smaller meteoroids observed by TV and radio methods.

Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

Abstract. Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011. The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April−August and to reach monthly-mean velocities of −12 m s−1. The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s−1 km−1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures. Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength. Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s−1 and 8 K and 20 m s−1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, AT and AW, that passed the Student T-test were found to be related by, AT = 0.34 AW and AT = 0.62 AW for the 16- and 5-day wave, respectively.

Some anomalies of mesosphere/lower thermosphere parameters during the recent solar minimum

Abstract. The recent solar minimum has been characterized by an anomalous strong decrease of thermospheric density since 2005. Here we analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. In particular, nighttime mean LF reflection heights measured at Collm, Germany, show a very strong decrease after 2005, indicating a density decrease. This decrease is also visible in mean meteor heights measured with VHF meteor radar at Collm. This density decrease is accompanied by an increase of gravity wave (GW) amplitudes in the upper mesosphere and a decrease in the lower thermosphere. On the decadal scale, GWs are negatively correlated with the background zonal wind, but this correlation is modulated in the course of the solar cycle, indicating the combined effect of GW filtering and density decrease.

Variation of sporadic meteor background and solar activity

Observations of the sporadic background meteors in 1996-2007 by the Bologna-Lecce-Modra forward-scatter radio system operating along two baselines are analyzed and discussed. The activity curves of sporadic meteor echoes and their variations indicate a direct correlation with the solar activity represented by the sunspot relative number R , as well as with the solar coronal index CI . The mass distribution exponents and its variations in the period of the 23rd solar cycle indicate a relatively stable population of the sporadic background meteoroid population in the surroundings of the Earth’s orbit. Investigation of meteor heights compiled from the IAU MDC catalogue of precise photographic orbits for a period of five solar cycles do not exhibit any pronounced variation consistent with the solar cycle activity.

Gravity wave–tidal interactions in the mesosphere and lower thermosphere over Rothera, Antarctica (68°S, 68°W)

A simple technique for measuring gravity wave activity has been used to investigate gravity wave–tidal interactions in the polar mesosphere and lower thermosphere (MLT). The technique uses the radial velocities of individual meteors recorded by meteor radar to derive a statistical measure (variance) of the activity of the high‐frequency gravity wave field. This technique can measure gravity waves with horizontal wavelengths of up to about 400 km and periods up to approximately 3 hours. Interactions between the observed gravity wave field and the background wind are investigated using data collected between February 2005 and December 2008 by a meteor radar based at Rothera, Antarctica (68°S, 68°W). The results reveal the presence of significant modulations of the observed gravity wave field at tidal periods of 12 and 24 hours. Correlations between the hourly zonal winds and the gravity wave field measured by the meteor radar reveal an in‐phase relationship between the hourly zonal winds and gravity wave variance in winter and an anti‐phase relationship in summer. This is consistent with the theory of filtering by tidal winds acting on a zonally‐asymmetric gravity wave field in which westward waves dominate in winter and eastward waves dominate in summer. The limitations of the technique and the effect this has on the interpretation of these results are also considered. The effects of the diurnal cycles in meteor count rates, the uncertainty in recorded radial velocities and the uncertainty in the measured heights of meteors are considered.

Seasonal and diurnal variation of electron and iron concentrations at the meteor heights above Arecibo

We report observations of seasonal and local time variation of the averaged electron and iron concentrations, as well as simultaneous measurements of the two species, above the Arecibo Observatory (18.35°N, 66.75°N), Puerto Rico. The average Fe profile between 21:00 and 24:00 LT has a single peak at about 85 km with the exception of the summer when an additional peak exists at about 95 km. The higher Fe peak in the summer is correlated with higher electron concentrations in this season. The three nights of simultaneous measurements of electron and iron concentrations show that narrow layers of Fe and electrons are well correlated. Comparison of the climatological and simultaneous Fe and electron data suggests that recombination of Fe + plays an important role in determining the Fe profile in the upper part of the Fe layer. Above 93 km, the Fe concentration appears to increase after sunset if the electron concentration exceeds about 4000 electrons cm −3. The average rate of Fe production is about 0.1 atom cm −3 s −1 for all seasons at 100 km in the early evening hours. A chemical model reveals that the concentration of Fe + must be 50–80% of the total ionization over Arecibo for typical equinox conditions to explain the observed rate of Fe production. These high relative Fe + concentrations are consistent with in situ observations that Fe + is usually the dominant ion in sporadic E layers in the nighttime lower E region. This suggests that the source of Fe + is provided by sporadic E layers descending over Arecibo after sunset. The Fe density between 80 and 85 km decreases during the night, for all seasons. This is attributed to the formation of stable molecular Fe species, such as FeOH, due to the increase in O 3 and decrease in atomic O and H during the night at these altitudes.

The beginning heights and light curves of high-altitude meteors

Abstract— In this paper, we provide an overview of meteors with high beginning height. During the recent Leonid meteor storms, as well as within the regular double station video observations of other meteor showers, we recorded 164 meteors with a beginning height above 130 km. We found that beginning heights between 130 and 150 km are quite usual, especially for the Leonid meteor shower. Conversely, meteors with beginning heights above 160 km are very rare even among Leonids. From the meteor light curves, we are able to distinguish two different processes that govern radiation of the meteors at different altitudes. Light curves vary greatly above 130 km and exhibit sudden changes in meteor brightness. Sputtering from the meteoroid surface is the dominating process during this phase of the meteor luminous trajectory. Around 130 km, the process switches to ablation and the light curves become similar to the light curves of standard meteors. The sputtering model was successfully applied to explain the difference in the beginning heights of high-altitude Leonid and Perseid meteors. We show also that this process in connection with high altitude fragmentation could explain the anomalously high beginning heights of several relatively faint meteors.

Properties of meteoroids from different classes of parent bodies

AbstractMeteoroids observed to disintegrate in the terrestrial atmosphere can be directly linked to their parent bodies in case that they belong to certain meteor showers. We present a list of two dozens of parent bodies reliably associated with well recognized meteor showers. Among the parent bodies are long period comets, Halley-type comets, Jupiter family comets, comets of the inner solar system (such as 2P/Encke) and asteroids. Physical and chemical properties of meteoroids coming from various parents are compared on the basis of meteor heights, decelerations, light curves and spectra. Jupiter family comets produce meteoroids with the lowest strength, namely porous aggregates of dust grains with bulk densities of about 0.3 g cm−3or less. Halley type material is somewhat stronger and the material related to comet Encke is even stronger. In addition, small strong constituents, perhaps similar to carbonaceous chondrites, can be encountered within the normal cometary material. The strength of cometary material is also enhanced by long-term exposure to cosmic rays and by solar heating in the vicinity to the Sun (r<0.2 AU). Both these processes lead to the loss of volatile sodium. Southern δ-Aquariids, Geminids and partly also Quadrantids were influenced by solar radiation. We argue that these showers, the asteroids associated with them ((3200) Phaethon and 2003 EH1), and the whole interplanetary complexes they belong to are of cometary origin. The argument is supported by lower than chondritic Fe/Mg ratio found in Geminids as well as in Halley type comets. The typical property of stony meteoroids of asteroidal origin is the presence of internal cracks which cause that the incoming meteoroids are much weaker than the recovered meteorites.

Radiants of the Leonids 1999 and 2001 Obtained by Lltv Systems Using Automatic Software Tools

Both amateur and professional meteor groups are more frequently using Low-Light level TV (LLTV) systems to record meteors. Double-station observations can yield orbit data. However, data analysis normally is still done by hand and thus time consuming. This paper addresses the question of whether available automated tools can be used to determine reasonably accurate orbits with minimum human intervention. The European Space Agency performed several observing campaigns to observe the Leonid meteor stream. In November 1999, the ESA meteor group was stationed at two locations in Southern Spain, in November 2001 at two stations close to Broome in North-Western Australia. Double-station observations with LLTV systems were conducted. The data was recorded on S-VHS video tapes. The tapes were processed using automatic detection software from which meteor heights, velocities and radiants were computed. This paper shows the results for the two maximum nights. The radiants determined in 1999 show a very large scatter due to unfortunate observing geometry and inaccurate position determination since one of the cameras was moving because of the wind. The 2001 data is excellent and the radiant was determined to be at RA = 153.96°±0.3° and Dec = 21.09°±0.2°. The error bars for individual meteor radiants are about 0.2° to 0.4°. This demonstrates that is indeed possible to determine good radiant positions using totally automated tools. Orbits, on the other hand, are not well defined due to the fact that the velocity of individual meteors shows large errors. Reasons for this are described.