scholarly journals <i>Letter to the Editior</i>Testing the hypothesis of the influence of neutral turbulence on the deduction of ambipolar diffusivities from meteor trail expansion

2005 ◽  
Vol 23 (3) ◽  
pp. 1071-1073 ◽  
Author(s):  
C. M. Hall ◽  
T. Aso ◽  
M. Tsutsumi ◽  
S. Nozawa ◽  
A. H. Manson ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Lower Thermosphere ◽  
Radar Echoes ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. Fading times of radar echoes from underdense meteor trails in the upper mesosphere/lower thermosphere are commonly used to determine ambipolar diffusivities and hence ambient temperature. Diffusivities are generally expected to increase exponentially with height through the region from which the meteor trail echoes are obtained, viz., typically 70-110km altitude for a ~30-MHz radar. In practice, however, this is more the exception: unexpectedly large diffusivities are obtained in the lower part of the regime, and unexpectedly low values are obtained in the upper part; only in the few kilometres on either side of the maximum in echo occurrence (viz., 90km for a 30-MHz radar) does the diffusivity profile behave as expected. Hall (2002) hypothesised that neutral turbulence might be enhancing expansion of the meteor trail in the lower part of the regime. In this communication, due to results only available since the publication of Hall's suggestion, we are able to refute the hypothesis.

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

2008 ◽  
Vol 26 (11) ◽  
pp. 3439-3443 ◽  
Author(s):  
A. P. Ballinger ◽  
P. B. Chilson ◽  
R. D. Palmer ◽  
N. J. Mitchell
Keyword(s):  
Ambient Temperature ◽  
Decay Time ◽  
Ambipolar Diffusion ◽  
Northern Sweden ◽  
Mesopause Region ◽  
Decay Times ◽  
Meteor Trail ◽  
Temperature And Pressure ◽  
Ion Recombination ◽  
Meteor Trails

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.

scholarly journals On the influence of neutral turbulence on ambipolar diffusivities deduced from meteor trail expansion

2002 ◽  
Vol 20 (11) ◽  
pp. 1857-1862 ◽  
Author(s):  
C. M. Hall
Keyword(s):  
Middle Atmosphere ◽  
Atmospheric Dynamics ◽  
Meteorology And Atmospheric Dynamics ◽  
Middle Atmosphere Dynamics ◽  
Radar Echoes ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect the meteor trail diffusion rate.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence)

scholarly journals Novel specular meteor radar systems using coherent MIMO techniques to study the mesosphere and lower thermosphere

2019 ◽  
Vol 12 (4) ◽  
pp. 2113-2127 ◽  
Author(s):  
Jorge Luis Chau ◽  
Juan Miguel Urco ◽  
Juha Pekka Vierinen ◽  
Ryan Andrew Volz ◽  
Matthias Clahsen ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Lower Thermosphere ◽  
Atmospheric Parameters ◽  
Angle Of Arrival ◽  
Independent Observations ◽  
Mesosphere And Lower Thermosphere ◽  
Meteor Trails ◽  
Transmitting Antenna ◽  
Mlt Region

Abstract. Typical specular meteor radars (SMRs) use one transmitting antenna and at least a five-antenna interferometric configuration on reception to study the mesosphere and lower thermosphere (MLT) region. The interferometric configuration allows the measurement of the angle-of-arrival (AOA) of the detected meteor echoes, which in turn is needed to derive atmospheric parameters (e.g., mean winds, momentum fluxes, temperatures, and neutral densities). Recently, we have shown that coherent MIMO configurations in atmospheric radars, i.e., multiple input (transmitters) and multiple output (receivers), with proper diversity in transmission can be used to enhance interferometric atmospheric and ionospheric observations. In this study we present novel SMR systems using multiple transmitters in interferometric configuration, each of them employing orthogonal pseudorandom coded transmitted sequences. After proper decoding, the angle of departure (AOD) of the detected meteor echoes with respect to the transmitter site are obtained at each receiving antenna. We present successful bistatic implementations of (1) five transmitters and one receiver using coded continuous wave (CW) (MISO-CW), and (2) five transmitters and five receivers using coded CW (MIMO-CW). The latter system allows simultaneous independent observations of the specular meteor trails with respect to the transmitter (AOD) and with respect to the receiver (AOA). The quality of the obtained results is evaluated in terms of the resulting mean winds, the number of detections and the daily diffusion trail vs. altitude behavior. We show that the proposed configurations are good alternatives to explore the MLT region. When combined with multi-static approaches, they can increase the number of meteor detections, thereby improving the quality of atmospheric estimates and allowing the measurement of new atmospheric parameters (e.g., horizontal divergence, vorticity), The use of multiple collocated transmitters for interferometric AOD determination makes building a multi-static radar network easier logistically, as only one receiver per receiving site antenna is sufficient.

scholarly journals Decay times of transitionally dense specularly reflecting meteor trails and potential chemical impact on trail lifetimes

2016 ◽  
Vol 34 (12) ◽  
pp. 1119-1144 ◽  
Author(s):  
Wayne K. Hocking ◽  
Reynold E. Silber ◽  
John M. C. Plane ◽  
Wuhu Feng ◽  
Marcial Garbanzo-Salas
Keyword(s):  
High Temperature ◽  
Ambient Temperature ◽  
Decay Times ◽  
The Subject ◽  
The Mean ◽  
Latitudinal Variations ◽  
Meteor Trails ◽  
Causative Relation ◽  
High Temperature Chemistry ◽  
Best Parameters

Abstract. Studies of transitionally dense meteor trails using radars which employ specularly reflecting interferometric techniques are used to show that measurable high-temperature chemistry exists at timescales of a few tenths of a second after the formation of these trails. This is a process which is distinct from the ambient-temperature chemistry that is already known to exist at timescales of tens of seconds and longer in long-lived trails. As a consequence, these transitionally dense trails have smaller lifetimes than might be expected if diffusion were the only mechanism for reducing the mean trail electron density. The process has been studied with four SKiYMET radars at latitudes varying from 10 to 75° N, over a period of more than 10 years, 24 h per day. In this paper we present the best parameters to use to represent this behaviour and demonstrate the characteristics of the temporal and latitudinal variability in these parameters. The seasonal, day–night and latitudinal variations correlate reasonably closely with the corresponding variations of ozone in the upper mesosphere. Possible reasons for these effects are discussed, but further investigations of any causative relation are still the subject of ongoing studies.

scholarly journals Ablation in Meteors

1971 ◽  
Vol 13 ◽  
pp. 259-269
Author(s):  
V. N. Lebedinets
Keyword(s):  
Physical Theory ◽  
Line Density ◽  
Radar Observations ◽  
Electron Line ◽  
Ablation Mechanism ◽  
Meteor Trail ◽  
Meteor Trails

Photographic and Radar Observations of meteors reveal essential discrepancies from the simplest physical theory of meteors. The simplest theory (Whipple, 1943; Herlofson, 1948; Kascheev et al., 1967) proceeds from the following suppositions: (1) the meteoroid is a dense non-fragmenting body; (2) the sole ablation mechanism is evaporation; and (3) the whole energy transferred to a body by colliding air molecules is spent on evaporation. In addition, the simplest theory of radiowave reflection from meteor trails that does not take into account diffusive and thermodiffusive expansion of a meteor trail and change of the electron line density along the trail is used for the interpretation of the results of radar observations.

scholarly journals Novel specular meteor radar systems using coherent MIMO techniques to study the mesosphere and lower thermosphere

2018 ◽  
Author(s):  
Jorge Luis Chau ◽  
Juan Miguel Urco ◽  
Juha Pekka Vierinen ◽  
Ryan Andrew Volz ◽  
Matthias Clahsen ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Lower Thermosphere ◽  
Atmospheric Parameters ◽  
Angle Of Arrival ◽  
Multiple Input ◽  
Independent Observations ◽  
Mesosphere And Lower Thermosphere ◽  
Meteor Trails ◽  
Transmitting Antenna

Abstract. Typical specular meteor radars (SMRs) uses one transmitting antenna and at least a five-antenna interferometric configuration on reception to study the mesosphere and lower thermosphere (MLT) region. The interferometric configuration allows the measurement of the angle-of-arrival (AOA) of the detected meteor echoes, which in turn is needed to derive atmospheric parameters (e.g., mean winds, momentum fluxes, temperatures, and neutral densities). Recently, we have shown that coherent MIMO configurations in atmospheric radars, i.e., Multiple Input (transmitters) and Multiple Output (receivers), with proper diversity in transmission can be used to enhance interferometric atmospheric and ionospheric observations. In this study we present two novel SMR systems using multiple transmitters in interferometric configuration, each of them employing orthogonal pseudo-random coded transmitted sequences. After proper decoding, the AOAs of the detected meteor echoes with respect to the transmitter site are obtained at each antenna of the receiver site. We present successful implementations of (1) five transmitters and one receiver using coded continuous wave (CW) (MISO-CW), and (2) five transmitters and five receivers using coded CW (MIMO-CW). The latter system allows simultaneous independent observations of the specular meteor trails with respect to the transmitter and with respect to the receiver. The quality of the obtained results is evaluated in terms of the resulting mean winds, the number of detections and the daily diffusion trail versus altitude behavior. We show that the proposed configurations can increase the number of meteor detections, thereby improving the quality of atmospheric estimates, and obtain new atmospheric parameters (e.g., horizontal divergence, vorticity, etc.), particularly when combined with multi-static approaches. The use of multiple collocated transmitters for interferometric AOA determination makes building a multi-static radar network logistically easier, as only one receiver antenna is sufficient for interferometric measurements.

scholarly journals Long-lived meteor trails

2019 ◽  
Vol 5 (3) ◽  
pp. 109-116
Author(s):  
Александр Михалев ◽  
Aleksandr Mikhalev ◽  
Александр Белецкий ◽  
Aleksandr Beletsky ◽  
Роман Васильев ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Magnetic Activity ◽  
Frequency Of Occurrence ◽  
Neutral Atmosphere ◽  
Dynamic Changes ◽  
Global Dynamic ◽  
Wave Disturbances ◽  
Meteor Trails ◽  
Thermodynamic Processes

Using vertical sounding data obtained by the Irkutsk digisonde DPS-4 from 2003 to 2016, we have studied the frequency of occurrence of the F1 layer in winter conditions. The frequency of occurrence of the F1 layer in December–January is shown to be more than twice lower than that in February at any level of magnetic activity. At moderate and low solar activity under quiet geomagnetic conditions, the appearance of F1 layer in midlatitudes of the Northern Hemisphere may be caused by active thermodynamic processes, which lead to transformation or destruction of the circumpolar vortex at heights of the middle atmosphere. Such global dynamic changes occurring in the winter strato-mesosphere are often associated with sudden stratospheric warming events, which are accompanied by increased generation of atmospheric waves of various scales. These wave disturbances can propagate upward to the heights of the lower thermosphere and ionosphere, carrying a significant vertical flow of energy and causing variations in the composition, thermodynamic parameters of the neutral atmosphere and ionosphere.

scholarly journals Meteor trail characteristics observed by high time resolution lidar

2014 ◽  
Vol 32 (10) ◽  
pp. 1321-1332 ◽  
Author(s):  
Y. J. Liu ◽  
J. M. C. Plane ◽  
B. R. Clemesha ◽  
J. H. Wang ◽  
X. W. Cheng
Keyword(s):  
Peak Height ◽  
Decay Process ◽  
High Time Resolution ◽  
Height Distribution ◽  
Double Peak ◽  
Data Set ◽  
Sodium Layer ◽  
Density Enhancement ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. We report and analyse the characteristics of 1382 meteor trails based on a sodium data set of ~ 680 h. The observations were made at Yanqing (115.97° E, 40.47° N), China by a ground-based Na fluorescence lidar. The temporal resolution of the raw profiles is 1.5 s and the altitude resolution is 96 m. We discover some characteristics of meteor trails different from those presented in previous reports. The occurrence heights of the trails follow a double-peak distribution with the peaks at ~ 83.5 km and at ~ 95.5 km, away from the peak height of the regular Na layer. 4.7% of the trails occur below 80 km, and 3.25% above 100 km. 75% of the trails are observed in only one 1.5 s profile, suggesting that the dwell time in the laser beam is not greater than 1.5 s. The peak density of the trails as a function of height is similar to that of the background sodium layer. The raw occurrence height distribution is corrected taking account of three factors which affect the relative lifetime of a trail as a function of height: the meteoroid velocity (which controls the ratio of Na/Na+ ablated); diffusional spreading of the trail; and chemical removal of Na. As a result, the bi-modal distribution is more pronounced. Modelling results show that the higher peak corresponds to a meteoroid population with speeds between 20 and 30 km s−1, whereas the lower peak should arise from much slower particles in a near-prograde orbit. It is inferred that most meteoroids in this data set have masses of ~ 1 mg, in order for ablation to produce sufficient Na atoms to be detected by lidar. Finally, the evolution of longer-duration meteor trails is investigated. Signals at each altitude channel consist of density enhancement bursts with the growth process usually faster than the decay process, and there exists a progressive phase shift among these altitude channels.

The effect of attachment on radio echo observations of meteors

1959 ◽  
Vol 253 (1272) ◽  
pp. 130-139 ◽  
Keyword(s):  
Light Intensity ◽  
Electron Density ◽  
Diffusion Processes ◽  
Diffusion Theory ◽  
Electron Attachment ◽  
Companion Paper ◽  
A Value ◽  
Meteor Trail ◽  
Meteor Trails ◽  
Attachment Coefficient

This paper is concerned with the effects of electron attachment to neutral air molecules on the characteristics of radio echoes from meteor trails. Previously it has been assumed that diffusion processes were primarily responsible for the reduction of volume electron density in a meteor trail, and also in limiting the echo duration. In a companion paper a value of the attachment coefficient β e = 5 x 10 -15 cm 3 s -1 has been determined from combined photo­graphic and radio echo observations of a meteor. An effect of an attachment coefficient of this magnitude is to reduce the expected echo duration by a factor of 1000 or more for a bright fireball. The observed relation between visual meteor magnitude and echo duration is explained by this mechanism, as are the departures from the wavelength squared variation of echo dura­tion predicted by diffusion theory. Attachment processes also account for the observation that the final heights of enduring meteor echoes all centre about 95 km, even though bright meteors may show a maximum in light intensity below 80 km.

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