Effect of neutral winds on the creation of non-specular meteor trail echoes

Non-specular meteor trail echoes are radar reflections from plasma instabilities that are caused by field-aligned irregularities. Meteor simulations are examined to show that these plasma instabilities, and thus the associated meteor trail echo, strongly depend on the meteoroid properties and the characteristics of the atmosphere in which the meteoroid is embedded. The effects of neutral winds, as a function of altitude, are analyzed to understand how their amplitude variability impacts the temporal–space signatures of non-specular meteor trail echoes present in very high-frequency (VHF) radar observations. It is found that amplitudes of the total horizontal neutral wind smaller than 0.6 m s−1 do not provide the right physical conditions to enable the genesis of non-specular meteor echoes. It is also found that a 0.0316 µg meteoroid traveling at 35 km s−1 can be seen as a meteor trail echo if the amplitudes of horizontal neutral winds are stronger than 15 m s−1. In contrast, a 0.316 µg meteoroid, traveling at the same speed, requires horizontal winds stronger than 1 m s−1 to be visible as a meteor trail echo. The neutral velocity threshold illustrates how simulations show that no trail echo is created below a critical wind value. This critical wind value is not mapped directly to radar observations, but it is used to shed light on the physics of meteor trails and improve their modeling. The meteor simulations also indicate that time delays on the order of hundreds of milliseconds or longer, between head echoes and non-specular echoes, which are present in VHF backscatter radar maps, can be a consequence of very dense plasma trails being affected by weak horizontal neutral winds that are smaller than 1 m s−1.

Studying a Long-Lasting Meteor Trail from Stereo Images and Radar Data

Unique observation of a long-lasting meteor trail of about half an hour duration is described. The trail resulted from a burning meteor from the Leonid storm flux in the middle latitudes over eastern Siberia. We describe three-dimensional morphological characteristics of both the meteor and the long-lasting trail using data from wide-angle CCD cameras. Additionally, we present the meteor and the trail radiolocation characteristics obtained with a meteor radar and ionosonde. The background dynamics of the upper atmosphere at the height where the long-lasting trail developed were observed using data from the meteor radar and Fabry-Perot interferometer. The obtained results allowed the conclusion that the dynamics of a long-lasting trail are conditioned by the wind. However, during the first minutes of trail development, it is possible that a high-speed component is present, resulting from explosion of the meteor body in the atmosphere. A primitive spectral analysis of the long-lasting trail's optical emissions and earlier studies point to hydroxyl molecules as a possible source of the glow. We believe the enhanced hydroxyl emission could be related to interaction of excited O(1D) oxygen atoms with meteor body water in the Earth's upper atmosphere.

Географическая привязка кадров широкоугольных оптических систем

A technique is described for referecing images of wide-angle optical systems intended for registration own radiation of the Earth's atmosphere, to geographic coordinates. The technique is based on an automatic procedure for the stars emphasing and identification in the frames and subsequent georeferencing. An example of the technique use for calculating the characteristics of a long-lived meteor trail based on observation data of two spatially separated wide-angle optical systems is shown.

Probabilistic analysis of ambiguities in radar echo direction of arrival from meteors

Meteors and hard targets produce coherent radar echoes. If measured with an interferometric radar system, these echoes can be used to determine the position of the target through finding the direction of arrival (DOA) of the incoming echo onto the radar. Depending on the spatial configuration of radar-receiving antennas and their individual gain patterns, there may be an ambiguity problem when determining the DOA of an echo. Radars that are theoretically ambiguity-free are known to still have ambiguities that depend on the total radar signal-to-noise ratio (SNR). In this study, we investigate robust methods which are easy to implement to determine the effect of ambiguities on any hard target DOA determination by interferometric radar systems. We apply these methods specifically to simulate four different radar systems measuring meteor head and trail echoes, using the multiple signal classification (MUSIC) DOA determination algorithm. The four radar systems are the Middle And Upper Atmosphere (MU) radar in Japan, a generic Jones 2.5λ specular meteor trail radar configuration, the Middle Atmosphere Alomar Radar System (MAARSY) radar in Norway and the Program of the Antarctic Syowa Mesosphere Stratosphere Troposphere Incoherent Scatter (PANSY) radar in the Antarctic. We also examined a slightly perturbed Jones 2.5λ configuration used as a meteor trail echo receiver for the PANSY radar. All the results are derived from simulations, and their purpose is to grant understanding of the behaviour of DOA determination. General results are as follows: there may be a region of SNRs where ambiguities are relevant; Monte Carlo simulation determines this region and if it exists; the MUSIC function peak value is directly correlated with the ambiguous region; a Bayesian method is presented that may be able to analyse echoes from this region; the DOA of echoes with SNRs larger than this region are perfectly determined; the DOA of echoes with SNRs smaller than this region completely fail to be determined; the location of this region is shifted based on the total SNR versus the channel SNR in the direction of the target; and asymmetric subgroups can cause ambiguities, even for ambiguity-free radars. For a DOA located at the zenith, the end of the ambiguous region is located at 17 dB SNR for the MU radar and 3 dB SNR for the PANSY radar. The Jones radars are usually used to measure specular trail echoes far from zenith. The ambiguous region for a DOA at 75.5∘ elevation and 0∘ azimuth ends at 12 dB SNR. Using the Bayesian method, it may be possible to analyse echoes down to 4 dB SNR for the Jones configuration when given enough data points from the same target. The PANSY meteor trail echo receiver did not deviate significantly from the generic Jones configuration. The MAARSY radar could not resolve arbitrary DOAs sufficiently well enough to determine a stable region. However, if the DOA search is restricted to 70∘ elevation or above by assumption, stable DOA determination occurs above 15 dB SNR.

Effect of neutral winds on the creation of non-specular meteor trail echoes

Non-specular meteor trail echoes are radar reflections from plasma instabilities that are caused by field-aligned irregularities. Meteor simulations are examined to show that these plasma instabilities, and thus the associated meteor trail echo, strongly depend on the meteoroid properties and the characteristics of the atmosphere in which the meteoroid is embedded. The effects of neutral winds, as a function of altitude, are analyzed to understand how their amplitude variability impacts the temporal-space signatures of non-specular meteor trail echoes present in VHF radar observations. It is found that amplitudes of the total horizontal neutral wind smaller than 0.6 m/s do not provide the right physical conditions to enable the genesis of non-specular meteor echoes. It is also found that a 0.0316 μg meteoroid traveling at 35 km/s can be seen as a meteor trail echo if the amplitudes of horizontal neutral winds are stronger than 15 m/s. In contrast, a 0.316 μg meteoroid, traveling at the same speed, requires horizontal winds stronger than 1 m/s to be visible as a meteor trail echo. The meteor simulations also indicate that time delays on the order of hundreds of milliseconds or longer, between head-echoes and non-specular echoes, which are present in VHF backscatter radar maps can be a consequence of very dense plasma trails being affected by weak horizontal neutral winds that are smaller than 1 m/s.

Probabilistic analysis of ambiguities in radar echo direction of arrival from meteors

Meteors and hard targets produce coherent radar echoes. If measured with an interferometric radar system, these echoes can be used to determine the position of the target through finding the Direction Of Arrival (DOA) of the incoming echo onto the radar. If the DOA of meteor trail plasma drifting with the ambient atmosphere is determined, the neutral wind at the observation altitude can be calculated. Specular meteor trail radars have become widespread scientific instruments to study atmospheric dynamics. Meteor head echo measurements also contribute to studies of the atmosphere as the meteoroid input of extraterrestrial material is relevant for a plethora of atmospheric phenomena. Depending on the spatial configuration of radar receiving antennas and their individual gain patterns, there may be an ambiguity problem when determining the DOA of an echo. Radars that are theoretically ambiguity free are known to still have ambiguities that depend on the total radar Signal to Noise Ratio (SNR). In this study we investigate robust methods which are easy to implement to determine the effect of ambiguities on any hard target DOA determination by interferometric radar systems. We apply these methods specifically to simulate four different radar systems measuring meteor head and trail echoes using the multiple signal classification (MUSIC) DOA determination algorithm. The four radar systems are the middle and upper atmosphere (MU) radar in Japan, a generic Jones 2.5λ specular meteor trail radar configuration, the Middle Atmosphere Alomar Radar System (MAARSY) radar in Norway and the The Program of the Antarctic Syowa Mesosphere Stratosphere Troposphere Incoherent Scatter (PANSY) radar in the Antarctic. We also examined a slightly perturbed Jones 2.5λ configuration used as a meteor trail echo receiver for the PANSY radar. All the results are derived from simulations and their purpose is to grant understanding of the behaviour of DOA determination. General results are: there may be a region of SNRs where ambiguities are relevant; Monte Carlo simulation determines this region and if it exists; the MUSIC function peak value is directly correlated with the ambiguous region; a Bayesian method is presented that may be able to analyse echoes from this region; the DOA of echoes with SNRs larger then this region are perfectly determined; the DOA of echoes with SNRs smaller then this region completely fail to be determined; the location of this region is shifted based on the total SNR versus the channel SNR in the direction of the target; asymmetric subgroups can cause ambiguities even for ambiguity free radars. For a DOA located at the zenith, the end of the ambiguous region is located at 17 dB SNR for the MU radar and 3 dB SNR for the PANSY radar. The Jones radars are usually used to measure specular trail echoes far from zenith. The ambiguous region for a DOA at 75.5° elevation and 0° azimuth ends at 12 dB SNR. Using the Bayesian method it may be possible to analyse echoes down to 4 dB SNR for the Jones configuration, given enough data points from the same target. The PANSY meteor trail echo receiver did not deviate significantly from the generic Jones configuration. The MAARSY radar could not resolve arbitrary DOAs sufficiently well to determine a stable region. However, if the DOA search is restricted to 70° elevation or above by assumption, stable DOA determination occurs above 15 dB SNR.

A technique for reconstructing the spatial characteristics of a long-lived meteor trails on all-sky cameras

<p>Over the years, reports of meteor trails lasting up to one hour have periodically appeared in the literature. These observations are usually associated with particularly strong meteor showers, such as Leonids. In [Kelley et al. 2000] some interesting observations of such trails related to the 1998 Leonid meteor shower event are presented [2]. In publications devoted to the study of this phenomenon in the optical range, the main attention is paid to processes that cause a prolonged luminescence of meteor showers [Kelley et al., 2000]. Meanwhile, this phenomenon is of great interest for diagnosing the Earth upper atmosphere state and the ionosphere. The bulk of the work in this direction is based on radar observations of ionization traces, the duration of which in some cases reaches several minutes [Kashcheev et al., 1967].</p><p>This paper reports on long-lived meteor trails (LMT), which was recorded simultaneously using two optical instruments recording night sky emissions. The first all-sky camera is located at the Geophysical Observatory of the ISTP SB RAS, near the Tory (51.80 N, 103.10 E) and is designed to record the spatial picture of the 630 nm emission intensity [http: // atmos. iszf.irk.ru/ru/data/keo]. The second all-sky camera is located in the Sayan Solar Observatory of the ISTP SB RAS, near the Mondy (51.60 N, 100.90 E). A meteor trail lasting 35-40 minutes was recorded on November 18, 2017 after a meteoroid explosion on 22.23.19 UT with two cameras from different directions. Further, an algorithm was developed with the Python programming language the geographical coordinates of this event were calculated, as well as the height of the highlight</p><p>. The meteoroid explosion height and the ellipsoidal trail was being 65-70 km. Then the meteor track bow spread horizontally in a southward for 30-40 minutes at an average velocity of 58 m/s. This technique can be used to determine the main characteristics of various phenomena in the atmosphere, such as waves, SAR-arcs, meteor tracks and others.</p><p>This work was supported by a grant from the Russian Foundation for Basic Research N19-35-90093.</p>

Mesospheric anomalous diffusion during noctilucent cloud scenarios

The Andenes specular meteor radar shows meteor trail diffusion rates increasing on average by about 10 % at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC after exploring possible contributions from thermal tides. To make this claim, the current study evaluates data from three stations at high, middle, and low latitudes for the years 2012 to 2016 to show that NLC influence on the meteor trail diffusion is independent of thermal tides. The observations also show that the meteor trail diffusion enhancement during NLC cover exists only at high latitudes and near the peaks of NLC layers. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that the relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars at high latitudes.