Meteor Rates Research Articles

Modeling the 2022 τ-Herculid Outburst

The τ-Herculids (IAU shower number 61 TAH) is a minor meteor shower associated with comet 73P/Schwassmann–Wachmann 3, a Jupiter-family comet that disintegrated into several fragments in 1995. As a consequence of the nucleus breakup, possible increased meteor rates were predicted for 2022. On May 30–31, observation networks around the world reported two distinct peaks of TAH activity, around solar longitudes 69.°02 and 69.°42. This work examines the encounter conditions of the Earth with meteoroids ejected from 73P during the splitting event and on previous perihelion passages. Numerical simulations suggest that the main peak observed in 2022 was caused by meteoroids ejected from the splitting nucleus with four times the typical cometary gas expansion speed. High-resolution measurements performed with the Canadian Automated Meteor Observatory indicate that these meteoroids are fragile, with estimated bulk densities of 250 kg m−3. In contrast with the main peak, the first TAH activity peak in 2022 is best modeled with trails ejected prior to 1960. We find that ordinary cometary activity could have produced other TAH apparitions observed in the past, including in 1930 and 2017. The extension of our model to future years predicts significant returns of the shower in 2033 and 2049.

Reaching Out: Using Social Media to Recruit ‘Invisible Groups’: The Case of South Asian Women in the UK Experiencing Gender-Related Violence

The rise of social media use has been phenomenal, particularly during the recent COVID-19 pandemic. Furthermore, Facebook has also seen its share of users rise at a meteoric rate. At the same time, the academy is producing a growing body of literature concerning the use of online methods for primary data collection. Yet, despite the increase in the use of the internet as a research tool, very little still exists on the use of social media to recruit research participants, particularly those deemed “socially invisible”. This paper addresses this gap. Another research project explored the experiences of South Asian women who had departed the social norms of arranged marriage to form an intimate relationship with a partner of choice and who then experienced forms of gender-related violence (GRV). The project encountered difficulties in recruiting participants from this marginalised and often invisible group in UK society, who are often too frightened or ashamed to come forward. This study demonstrates how to use Facebook ethically and methodologically, highlighting some of the methods used to overcome the challenges that were presented. The research was undertaken before the COVID-19 pandemic (which prompted a widespread use of social media in social science research). We argue that, despite the ethical challenges, the advantages of using social media to recruit participants when researching a highly sensitive topic such as GRV with ‘invisible groups’ was highly beneficial. We therefore suggest that social media should be an integral part of the research recruitment process, alongside non-digital methods, so that other ‘invisible groups’ are not created comprising those who cannot access technology. We share the lessons learned for the benefit of researchers using a similar approach today when recruiting research participants from invisible and marginalised groups. The authors caveat their recommendation of using social media with suggesting that those who do not have high levels of experience of data collection with such cohorts instead consider working with gatekeepers to facilitate the recruitment.

Countering online hate speech through legislative measures: The Ethiopian approach from a comparative perspective

ABSTRACT It is apparent that the phenomenon of online hate speech is increasing at a meteoric rate. Meanwhile, governments around the world are resorting to legislative measures in an attempt to address this pernicious social problem. Yet, while much of the discourse has been on how these legislative efforts may inadvertently affect individuals’ right to freedom of expression in established liberal democracies, little is known about the collateral costs of similar trends in developing countries with a burgeoning democratic culture. For this reason, it is imperative to assess how and to what extent legal frameworks for the moderation of user-generated online content may portend dire consequences for freedom of speech in non-democratic countries like Ethiopia, where there are distinct media and socio-political environments. Using comparative legal research methodology, this research article seeks to offer an overview of the legislative responses to online hate speech in different jurisdictions, drawing from normatively preferable policy frameworks, to provide some insights into how gaps in the new Ethiopian hate speech and disinformation prevention law can be filled.

Geomagnetic and Solar Dependencies of Midlatitude E‐Region Irregularity Occurrence Rate: A Climatology Based on Wuhan VHF Radar Observations

AbstractBy using Wuhan VHF radar, we show the morphological features of E‐region field‐aligned irregularity (FAI) occurrence at Wuhan during 2015–2020. Statistical results present that E‐region FAI occurrence reaches a maximum after sunset in summer season. According to Doppler spectrum features, type‐2 irregularity is predominantly observed at Wuhan. In addition, we observed a remarkable correlation between E‐region FAI occurrence and geomagnetic activity, which includes periods of positive correlation and negative correlation depending on different geomagnetic conditions. The strong negative correlation also exists between E‐region FAI occurrence and solar activity. In our observed results, we find that E‐region FAI occurrence shows a strong linkage with local sporadic E (ES) layer. A quantitative analysis of linear theory of plasma instability in the E‐region at midlatitudes is also presented in our study. The calculated results of linear growth rate indicate the importance of plasma density gradient of local ES layer and field‐line‐integrated Pedersen conductivity on the generation of E‐region FAI. The geomagnetic and solar variations of E‐region FAI occurrence are also discussed in this study, which show a dependence on the geomagnetic and solar variations of both meteor rate and medium‐scale traveling ionospheric disturbance occurrence.

Long‐Term Observations and Physical Processes in the Moon's Extended Sodium Tail

AbstractThe lunar surface is constantly bombarded by the solar wind, photons, and meteoroids, which can liberate Na atoms from the regolith. These atoms are subsequently accelerated by solar photon pressure to form a long comet‐like tail opposite the sun. Near new moon, these atoms encounter the Earth's gravity and are “focused” into a beam of enhanced density. This beam appears as the ∼3° diameter Sodium Moon Spot (SMS). Data from the all sky imager at the El Leoncito Observatory have been analyzed for changes in the SMS shape and brightness. New geometry‐based relationships have been found that affect the SMS brightness. The SMS is brighter when the Moon is north of the ecliptic at new moon; the SMS is brighter when new moon occurs near perigee; and the SMS peaks in brightness ∼5 h after new moon. After removing these effects, the data were analyzed for long term and seasonal patterns that could be attributed to changes in source mechanisms. No correlation was found between the SMS brightness and the 11‐year solar‐cycle, the proton or the He++ flow pressure, the density, the speed or the plasma temperature of the solar wind, but an annual pattern was found. A ∼0.83 correlation (Pearson's “r”) was found between the SMS brightness and a 4‐year average of sporadic meteor rates at Earth, suggesting a cause‐and‐effect. The new insights gained from this long‐term study put new constraints on the variability of the potential sources of the Na atoms escaping from the Moon.

Modeling the past and future activity of the Halleyid meteor showers

Context.We present a new numerical model of theη-Aquariid and Orionid meteor showers.Aims.The model investigates the origin, variability, and age of theη-Aquariid and Orionid apparitions from 1985 to the present day in order to forecast their activity over the next several decades.Methods.Through the numerical integration of millions of simulated meteoroids and a custom-made particle weighting scheme, we model the characteristics of everyη-Aquariid and Orionid apparition between 1985 and 2050. The modeled showers are calibrated using 35 yr of meteor observations, including the shower activity profiles and interannual variability.Results.Our model reproduces the general characteristics of the present-dayη-Aquariids and part of the Orionid activity. Simulations suggest that the age of theη-Aquariids somewhat exceeds 5000 yr, while a greater fraction of the Orionids is composed of older material. The 1:6 mean motion resonance with Jupiter plays a major role in generating some (but not all) Halleyid stream outbursts. We find consistent evidence for a periodicity of 11.8 yr in both the observations and modeled maximum meteor rates for the Orionids. Weaker evidence of a 10.7 yr period in the peak activity for theη-Aquariids needs to be investigated with future meteor observations. The extension of our model to future years predicts no significant Orionid outbursts through 2050 and four significantη-Aquariid outbursts, in 2023, 2024, 2045, and 2046.

Solar cycle variation in radar meteor rates

ABSTRACT 16 yr of meteor radar data from the Canadian Meteor Orbit Radar (CMOR) were used to investigate the link between observed meteor rates and both solar and geomagnetic activity. Meteor rates were corrected for transmitter power and receiver noise, and seasonal effects were removed. A strong negative correlation is seen between solar activity, as measured with the 10.7 cm flux, and observed meteor rates. This lends support to the idea that heating in the atmosphere at times of elevated solar activity changes the scale height and therefore the length and maximum brightness of meteors; a larger scale height near solar maximum leads to longer, fainter meteors and therefore lower rates. A weaker negative correlation was observed with geomagnetic activity as measured with the K index; this correlation was still present when solar activity effects were removed. Meteor activity at solar maximum is as much as 30 per cent lower than at solar minimum, strictly due to observing biases; geomagnetic activity usually affects meteor rates by less than 10 per cent.

Luminosity function of faint sporadic meteors measured with a wide-field CMOS mosaic camera Tomo-e PM

Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of ∼1.98deg2 at 2 Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from +4 to +10mag in the V-band, corresponding to about 8.3×10−2 to 3.3×10−4g in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter r=3.1±0.4 and a meteor rate log10N0=−5.5±0.5. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozenis about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozenwill provide a more robust measurement of the luminosity function.

Meteor Observations at Kazan Federal University (Russia)

SummaryThis poster paper described initial results of recent meteor observations in Kazan obtained with a new meteor radar, SKiYMET. Significant improvements in the number of registrations are being recorded, enabling better statistics.Radar observations of meteors have been carried out and archived since the mid-20th Century; at Kazan University (56°N, 49°E) they commenced in 1956, and have continued with only a few interruptions. A quasi-tomographic method (developed in-house in 2000) has been used to determine the coordinates of radiants of meteor showers, and to derive the orbital elements of small showers (microshowers).The observations provide valuable information about the distribution of meteoric matter near the Earth’s orbit. That information supports studies of stratospheric temperatures. A new radar, SKiYMET, was deployed in 2015 and measured parameters such as meteor speeds, but in 2016 its software was supplemented by an in-house package which performed more efficient pre-filtering of the primary data to eliminate non-meteor reflections from various sources. The new filtering algorithm has reduced substantially the threshold S/N ratio for detecting meteors (so fainter meteors can now be recorded), while the package also enables meteor velocities to be calculated much more efficiently than with SKiYMET, improving significantly the quality and statistical indicators of the processed data. By detecting a much larger number of meteors, it enables more detailed studies of the distribution of meteor velocities per day and per season.Daily meteor counts for 2016–2017, extracted from the observations by the KFU programme, yielded significantly higher rates than with SKiYMET. These results support much better statistics, and also enable much finer details to be discerned. In particular, plots of meteor rates against speed are found to exhibit two maxima, one near 30 km s−1 and one near 55 km s−1. This bifurcation in the relationship can also be discerned in the seasonal dependences of the speed distribution.Improvements in the measurements of the speeds of meteor particles entering the atmosphere reveal an increase in the numbers with higher speeds (> 50 km s−1). The distributions of speeds and heights show a rather strong dependence of the meteor speed upon altitude; as predicted by meteor physics, those with higher speeds begin to burn at higher altitudes. A local increase in the number of meteors that have speeds of about 55 km s−1 has also been reported in the literature. The increase could be associated with heterogeneities in the distribution of meteoric matter in the vicinity of the Earth’s orbit.

The Cost of Hospital Admission: Brief Resolved Unexplained Events.

The modern health care system continues to expand at a meteoric rate with ever-increasing technological advancements. However, with these advancements come unsustainably rising costs and occasionally unintended, avoidable harm. In this article, we use a brief resolved unexplained event (BRUE) to illustrate how recent guidelines can help physicians practice value in this modern health care system. A BRUE is a common pediatric problem that is seen in ambulatory and emergency department settings. Infants presenting with a BRUE can be separated into low- and high-risk groups per recent guidelines. Most low-risk infants who present with a BRUE can be discharged home with anticipatory guidance, whereas high-risk infants should undergo further testing and admission to determine the cause of their event. [Pediatr Ann. 2017;46(7):e262-e264.].

Comparison of sporadic sodium layer characteristics observed at different time resolutions

Abstract. Sporadic sodium (Nas) layers, occurring in roughly the same height range as ionospheric sporadic-E layers, were first detected by lidar some 30 yr ago. Nas layers have a typical thickness of a few hundred meters to a few km, with peak atom concentrations several times that of the background layer. Despite a great deal of excellent work over the past decades, the source of Nas layers is still not altogether clear, partly as a result of our incomplete knowledge of Nas layer characteristics. In this paper we concentrate on some typical case studies chosen from the ~127 h of sporadic sodium layer observations made at a time resolution of 1.5 s at Yanqing (115.97° E, 40.47° N), Beijing, China. This is a much better time resolution than what has been employed in most earlier measurements. The results show that the Nas layer peak heights are dispersed at slightly different although adjacent heights. When averaged over several minutes, as has been the case with most earlier measurements, the height scatter results in an apparent layer thickness of a few km. We conclude, therefore, that these dispersed peaks at different but adjacent heights constitute the 5 min Nas layer. Similar to the observations of sporadic-E-ion (Es) layers and meteor rate, we observe quasi-periodic fluctuations on a timescale on the order of several minutes in the peak height and the peak density of sporadic layers, which is a universal feature but concealed by the lower temporal resolution previously adopted. Spatially localized multiple scatterers and multiple thin layers with similar apparent movement in Nas layers are also found. We discuss the possible formation mechanism by the direct deposition of large swarms of micrometeoroids and demonstrate a typical example of meteor trails evolving into a Nas layer, which suggests that this mechanism might indeed occur.

Radar observations of the 2011 October Draconid outburst

A strong outburst of the October Draconid meteor shower was predicted for 2011 October 8. Here we present the observations obtained by the Canadian Meteor Orbit Radar (CMOR) during the 2011 outburst. CMOR recorded 61 multistation Draconid echoes and 179 single-station overdense Draconid echoes (covering the magnitude range of +3 ≤ MV ≤ +7) between 16 and 20 h ut on 2011 October 8. The mean radiant for the outburst was determined to be αg = 261| $_{.}^{\circ}$|9 ± 0| $_{.}^{\circ}$|3, δg = +55| $_{.}^{\circ}$|3 ± 0| $_{.}^{\circ}$|3 (J2000) from observations of the underdense multistation echoes. This radiant location agrees with model predictions to ∼1°. The determined geocentric velocity was found to be ∼10–15 per cent lower than the model value (17.0–19.1 km s−1 versus 20.4 km s−1), a discrepancy we attribute to undercorrection for atmospheric deceleration of low-density Draconid meteoroids as well as to poor radar radiant geometry during the outburst peak. The mass index at the time of the outburst was determined to be ∼1.75 using the amplitude distribution of underdense echoes, in general agreement with the value of ∼1.72 found using the diffusion-limited durations of overdense Draconid echoes. The relative flux derived from overdense echo counts showed a similar variation to the meteor rate derived from visual observations. We were unable to measure the peak flux due to the high elevation of the radiant (and hence low elevation of specular Draconid echoes). Using the observed speed and electron line density measured by CMOR for all underdense Draconid echoes as a function of height as a constraint, we have applied the ablation model developed by Campbell-Brown & Koschny. From these model comparisons, we find that Draconid meteoroids at radar sizes are consistent with a fixed grain number ngrain = 100 and a variable grain mass mgrain between 2 × 10−8 and 5 × 10−7 kg, with bulk and grain density of 300 and 3000 kg m−3, respectively. One particular Draconid underdense echo displayed well-defined Fresnel amplitude oscillations at four stations. The internal synchronization allowing us to measure absolute length as a function of time by combining the absolute timing offsets between stations. This event showed clear deceleration and modelling suggests that the number of grains for this meteoroid was of the order of 1000 with grain masses between 10−10 and 10−9 kg, and a total mass of 2 × 10−6 kg.

Enhanced sporadic <i>E</i> occurrence rates during the Geminid meteor showers 2006–2010

Abstract. Northern Hemisphere midlatitude sporadic E (Es) layer occurrence rates derived from FORMOSAT-3/COSMIC GPS radio occultation (RO) measurements during the Geminid meteor showers 2006–2010 are compared with meteor rates obtained with the Collm (51.3° N, 13.0° E) VHF meteor radar. In most years, Es rates increase after the shower, with a short delay of few days. This indicates a possible link between meteor influx and the production of metallic ions that may form Es. There is an indication that the increase propagates downward, probably partly caused by tidal wind shear. However, the correlation between Es rates and meteor flux varies from year to year. A strong correlation is found especially in 2009, while in 2010 Es rates even decrease during the shower. This indicates that additional processes significantly influence Es occurrence also during meteor showers. A possible effect of the semidiurnal tide is found. During years with weaker tidal wind shear, the correlation between Es and meteor rates is even weaker.

Gravity wave flux retrievals using meteor radars

The ability of all‐sky interferometric meteor radars to measure mean wind and high‐frequency gravity wave wind perturbations from meteor radial velocities is assessed. A Monte‐Carlo technique that models line‐of‐sight meteor wind measurements with realistic errors in angle‐of‐arrival and range is used to investigate uncertainties in mean wind and gravity wave wind parameters as a function of meteor echo rate. It is shown that mean horizontal wind speeds are recovered with reasonable accuracy at meteor rates as low as 10 hr−1. Mean‐square horizontal wind perturbation can be derived with relatively little averaging, but momentum fluxes are recovered with much less accuracy, which means that considerable averaging is required to produce meaningful values. Results are illustrated using meteor wind radar observations taken over a 30‐day period in January–February 2006 in Northern Australia.

Periodic Variability of Visual Sporadic Meteor Rates

A long-term variability of visual sporadic meteor hourly rates is studied in the period between 1984 and 2006. The present analysis involves four particular periods of visual sporadic meteor activity in January, March, July and September over two solar cycles, and the results reveal that the observed visual sporadic meteor rates vary periodically in the course of the solar cycle. It is found that the highest sporadic meteor rates are observed in the years near solar activity maxima, and their variability directly correlates with solar activity expressed by International sunspot numbers.

Diurnal Variability Prediction Model of Meteor Burst Communication Channel

流星突发通信不同于传统的通信, 其是低速率通信, 具有突发、不连续、不定时的特性. 因此, 流星余迹通信的复杂性要求有必要对其通信信道进行建模. 在流星通信链路中, 流星的辐射分布、可用流星率和占空比是影响流星通信信道性能的重要参数. 流星辐射分布在不同季节不同时间都各不相同, 因此准确预测流星通信链路在不同时间的流星辐射分布, 从而改变大圆路径上天线的指向, 对提高通信速率显得非常重要. 同时, 准确预测流星突发通信链路上的可用流星率和占空比, 有助于准确预测并建立流星突发信道模型. 本文分析研究了偶发流星辐射分布建模的发展, 建立了偶发流星日心空间和地心空间的几何关系, 得到了流星突发通信信道参数预测模型. 并将预测模型应用于流星通信链路, 预测结果与通信链路观测结果比较一致, 为流星通信系统的建立提供了技术支持.

Seasonal and diurnal variability of the meteor flux at high latitudes observed using PFISR

We report in this and a companion paper [Fentzke, J.T., Janches, D., Sparks, J.J., 2008. Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.015] a complete seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena; for example, it could be the source of meteoric smoke that is thought to act as condensation nuclei in the formation of ice particles in the polar mesosphere. The observations presented here were performed for full 24-h periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes [Janches, D., Heinselman, C.J., Chau, J.L., Chandran, A., Woodman, R., 2006. Modeling of the micrometeor input function in the upper atmosphere observed by High Power and Large Aperture Radars, JGR, 11, A07317, doi:10.1029/2006JA011628]. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected every day. We show that meteor rates, altitude, and radial velocity distributions have a large seasonal dependence. This seasonal variability can be explained by a change in the relative location of the meteoroid sources with respect to the observer. Our results show that the meteor flux into the upper atmosphere is strongly anisotropic and its characteristics must be accounted for when including this flux into models attempting to explain related aeronomical phenomena. In addition, the measured acceleration and received signal strength distribution do not seem to depend on season; which may suggest that these observed quantities do not have a strong dependence on entry angle.

Latitudinal and seasonal variability of the micrometeor input function: A study using model predictions and observations from Arecibo and PFISR

In this work, we use a semi-empirical model of the micrometeor input function (MIF) together with meteor head-echo observations obtained with two high power and large aperture (HPLA) radars, the 430 MHz Arecibo Observatory (AO) radar in Puerto Rico (18°N, 67°W) and the 450 MHz Poker flat incoherent scatter radar (PFISR) in Alaska (65°N, 147°W), to study the seasonal and geographical dependence of the meteoric flux in the upper atmosphere. The model, recently developed by Janches et al. [2006a. Modeling the global micrometeor input function in the upper atmosphere observed by high power and large aperture radars. Journal of Geophysical Research 111] and Fentzke and Janches [2008. A semi-empirical model of the contribution from sporadic meteoroid sources on the meteor input function observed at arecibo. Journal of Geophysical Research (Space Physics) 113 (A03304)], includes an initial mass flux that is provided by the six known meteor sources (i.e. orbital families of dust) as well as detailed modeling of meteoroid atmospheric entry and ablation physics. In addition, we use a simple ionization model to treat radar sensitivity issues by defining minimum electron volume density production thresholds required in the meteor head-echo plasma for detection. This simplified approach works well because we use observations from two radars with similar frequencies, but different sensitivities and locations. This methodology allows us to explore the initial input of particles and how it manifests in different parts of the MLT as observed by these instruments without the need to invoke more sophisticated plasma models, which are under current development. The comparisons between model predictions and radar observations show excellent agreement between diurnal, seasonal, and latitudinal variability of the detected meteor rate and radial velocity distributions, allowing us to understand how individual meteoroid populations contribute to the overall flux at a particular location and season.

Annual and Diurnal Variation of Meteor Rates by the Forward-Scatter Radio Observation

Forward-scatter radio meteor observations have been made at Japan since 1996 using inexpensive and low-end equipment. The activity of some major meteor showers and the seasonal variability of sporadic meteors in 2006 are presented.

A semi‐empirical model of the contribution from sporadic meteoroid sources on the meteor input function in the MLT observed at Arecibo

In this paper, we present a modeling and observational study of the micrometeor input function with a focus on understanding how each of the extraterrestrial sporadic meteoroid sources contributes to the observed meteoric flux in the Mesosphere and Lower Thermosphere (MLT) atmospheric region. For this purpose, we expand the model presented by Janches et al. (2006) using a Monte Carlo technique and incorporating: 1) a widely accepted global mass flux, which is divided into different proportions among the known sporadic meteoroid sources as the initial input above Earth’s atmosphere; 2) contemporary knowledge on the source's velocity and radiant distributions; and 3) the full integration of the canonical meteor equations that describe the meteoroid entry and ablation physics. In addition, we constrain the initial input through a comparison of our modeled results with meteor observations obtained with the 430 MHz High Power and Large Aperture (HPLA) Arecibo radar in Puerto Rico that covers all seasons. The predicted meteor rates and velocity distributions are in excellent agreement with the observed ones without the need for any additional normalization factor. Our results indicate that although the Earth’s Apex centered radiant source, which is characterized by high geocentric speeds (∼55 km/s), appears to be ∼33% of the meteoroids in the Solar System at 1 AU, it accounts for ∼60% of the meteors observed by the Arecibo HPLA radar in the atmosphere. The remaining 40% of observed meteors originate mostly from the Helion and Anti‐Helion sources, with a very small, but constant during the day, contribution of the South and North Toroidal sources. These results also suggest that particles smaller than ∼10−3μg with slow velocities (<30 km/s) will not significantly ablate and never become observable meteors. The motivation of this effort is to construct a new and more precise MIF model needed for the subsequent modeling of the atmospheric phenomena related to the meteoric flux.