1998～2000年狮子座流星雨的预报和观测

"1998年狮子座流星雨可能是暴雨,最佳观测地在东亚"的预报,客观上加速了中国对流星雨的现代研究。几年来,对狮子座流星雨的观测和研究,是在全国狮子座流星雨联测小组的组织和领导下发展起来的。这包括使用目视方法、照相方法和无线电方法的观测,以及组织广大天文爱好者在全国范围内的观测。我们的确也观测到了很多重要的现象,如流星雨的纤维结构、尺度分布和质量密度分布的变化等等。我们发展了数据处理方法,将处理其它天文观测数据的"时间窗"方法移植到了流星雨的数据处理中。这一方法如今在流星雨研究中已经在世界上普遍使用了。我们还提出了流星雨的质量流参量ZHMR,它对于今后流星雨的观测比较和预报可能更加有用。在雷达观测方面,我们观测到了1998年所期待的流星雨强度主峰。在此主峰过了大约18h之后,又观测到了地球电离层的反常爆发。从1998年连续两天狮子座流星雨不同的表现,以及从全国不同地区的观测得到的流星质量分布系数的差异,我们提出了大、小2种不同粒子的混合流模型,很好地解释了观测到的现象。从天体力学的基本公式出发,我们发现流星群轨道升交点和其母彗星轨道升交点之差,不仅与当时的抛射速度,而且与彗星抛出这些尘埃粒子时在轨道上的位置有关。对于1998年的观测,最可能的是这些粒子是     

Video Observations of the 2006 Leonid Outburst

We carried out double station observations of the Leonid meteor shower outburst, which occurred in the morning hours of November 19, 2006. Using image-intensified cameras we recorded approximately 100 Leonid meteors. As predicted, the outburst was rich especially in fainter meteors. The activity profile shows that the peak of the outburst occurred at 4:40 ± 0:05 UT. The maximum reached flux was 0.03 meteoroids km⁻² hod⁻¹ for meteors brighter than +6.5 magnitude.     

近20年来狮子座流星雨预报进展

对近20年来狮子座流星雨的预报工作，进行了系统的阐述和分析。1998年Tempel-Tuttle彗星的回归，再度带来了狮子座流星雨的观测热，也大大促进了对狮子座流星雨预报工作的研究与验证。有的研究在时间预报准确度方面已显示出其模型的优越性，有的在流星雨的强度方面显示出一定的准确度。指出了两大类不同的方法实际上是在三维空间强调了不同的方面。将不同方法的优势结合起来，可能会使流星雨的预报更加成熟。     

Radar Observations of Taurid Complex Meteor Showers in 2003: Activity and Mass Distribution

Results of Ondřejov radar observation of Taurid complex meteor showers, i.e. ζ Perseids, β Taurids, S and N Taurids, performed in 2003, are presented. We have found some mass segregation within ζ Perseid, β Taurid and S Taurid showers. We have also established conspicuous lack of long duration echoes (with T ⩾ 3 s resp. T ⩾ 5 s) in S and N Taurid showers. The lack within remaining showers is not so pronounced but still persists.     

The Third Peak of the 1998 Leonid Meteor Shower

1 INTRODUCTIONThe Leonid meteor shower is a well-known periodic meteor shower. Its history is tied upwith the development of the theory of meteor stream astronomy itself. It was the very st.rongshowers of 1799 and 1833 that played a sghficant pat in the recoghtion of the ealstence ofmeteoroid streams. These evellts started the obse~ions of Leoaid meteor shower and broughtabout the birth of meteoritiCS. It is known that the Leould parent comet, 55P/Tempel-TUttle,has an orbital period a…     

Visual Observations Of The Leonid Meteors 1998 In Yunnan

The 1998 Leonid meteor shower was observed at the Gaomeigu station of Yunnan Observatory during five successive days in November. The visual records indicate that the number of meteors increased suddenly, from a ZHR of about 140 to over 400, in the early morning of November 17th, Beijing time. But it decreased slowly in the following two days. During the maximum there was a high proportion – about 10 percent – of very bright fireballs with enduring trains. The brightest one was about -10 magnitude with a smoke train fading about three minutes after. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contour Observations of the Leonid Shower in 1999

Contour visual observations of the Leonid meteor shower were made on December 18, 1999 by the method in which different groups of observers counted meteors in zenith, near the horizon, and observed through binoculars to study the luminosity function and the space density of the swarm. The luminosity function was obtained in the range of magnitudes from –8 ^m to +9 ^m . Over a wide range of magnitudes, the luminosity function is found to be nonlinear and is adequately approximated with a second-order curve. The logarithm of the meteor space density (m) reaches saturation at about 10 ^m , indicating that particles that give rise to meteors fainter than 10 ^m are absent in the swarm. The meteor stream reached its activity peak at a solar longitude of 235°, 287 (2 ^h 05 ^m UT). The peak visual zenithal hourly rate was about 7000 per one observer over an averaging interval of 1 min. The swarm space density increased by a factor of 6 within 0.5 hours and exceeded 600 particles per 10⁹ km³ for meteors brighter than +4 ^m . In the peak night, the luminosity-function exponent demonstrates no regular trend and reflects the intercepting of certain swarm clouds by the Earth.     

The Canadian Meteor Orbit Radar Meteor Stream Catalogue

The Canadian Meteor Orbit Radar is a multi-frequency backscatter radar which has been in routine operation since 1999, with an orbit measurement capability since 2002. In total, CMOR has measured over 2 million orbits of meteoroids with masses greater than 10 μg, while recording more than 18 million meteor echoes in total. We have applied a two stage comparative technique for identifying meteor streams in this dataset by making use of clustering in radiants and velocities without employing orbital element comparisons directly. From the large dataset of single station echoes, combined radiant activity maps have been constructed by binning and then stacking each years data per degree of solar longitude. Using the single-station mapping technique described in Jones and Jones (Mon Not R Astron Soc 367:1050–1056, 2006) we have identified probable streams from these single station observations. Additionally, using individual radiant and velocity data from the multi-station velocity determination routines, we have utilized a wavelet search algorithm in radiant and velocity space to construct a list of probable streams. These two lists were then compared and only streams detected by both techniques, on multiple frequencies and in multiple years were assigned stream status. From this analysis we have identified 45 annual minor and major streams with high reliability.     

Shower Meteoroids: Constraints From Interplanetary Dust Particles And Leonid Meteors

The cometary Leonid meteoroids represent a size range in between largest carbon-richIDPs and the smallest CI meteorites. Their dustball structure and chemistry offer anopportunity to constrain hierarchical dust accretion inferred from petrologic studies ofaggregate and cluster IDPs. The Leonid shower meteoroids of known ``comet ejection'ages provide an opportunity to study space weathering of cometary dust over periodsof up to several hundred years. The meteors and aggregate and cluster IDPs displaycontinuous thermal modification of organics and volatile element (Na, K-bearing phases), that occur as discrete minerals and amorphous solids each different response during kinetically controlled ablation. Leonid meteoroids are not excessively Na-rich. The occurrences of Leonid meteors can now be accurate predicted and combined withknowledge better models for the settling rates, collections of surviving dust becomea comet nucleus-sampling mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

流星雨摄影观测记录的罕见现象

2001年狮子座流星雨,是几百年来难得有机会在中国观测到的一场流星暴。在我们收集到的照相观测资料中,发现了一些特殊的、还未引起广泛注意的流星现象。"蛇行"的流星以及螺旋形并带有辐条结构的流星余迹,早在我国古代记录中就可以找到印证。现代的照相技术,不仅直观地显示了文字难以描述的颜色、形态和变化,而且提供了可永久性进行测量的记录。其中包括罕见的对流星余迹的双站观测资料。用常规的"高空风作用"难以解释这些观测现象。它们可能反映了流星带电体与地球磁场的相互作用。     

Spectroscopic Observations of the 2011 Draconids Meteor Shower

Some past October Draconid shower meteoroids fell apart in a spray of fragments at the end of their trajectory before slowing down, from which it was concluded that these were among the most fragile meteoroids known. In those instances, the dust could not be reliably traced to a particular return of the parent comet 21P/Giaconini-Zinner. On October 8th, 2011, Earth was predicted to transverse the 1900 A.D. dust ejecta of the comet. In 1900, the comet’s perihelion distance first moved significantly inwards to the Sun and ejection conditions could have been unusual. An airborne observing campaign was organized, with several teams contributing imaging and spectrographic cameras to study the manner in which these meteoroids released the volatile element sodium during the ablation process in the Earth’s atmosphere. IMCCE, ESA, and the SETI Institute contributed spectrographic cameras based on low-light WATEC 902H2 Ultimate, low-light LCC1, and GenII XX1332 image intensified cameras. An outburst was observed, much as predicted. Despite a lack of bright meteors, a total of 15 Draconid spectra were recorded. All show evidence of an early release of sodium. The loss of sodium was observed to coincide with the formation of a distinct wake of fragments. The observations show that 21P/Giacobini-Zinner ejected fragile meteoroids during the return in 1900. Those grains may have lost some sodium even before impacting Earth.     

Geminid Meteor shower activity 2003–2005 as observed by Gadanki radar

The distribution of meteor signals reflected from a backscatter radar is considered according to their duration. This duration time (T) is used to classify the meteor echoes and to calculate the mass index (S) of different meteoroids of shower plus sporadic background. Observational data on particle size distribution of the Geminid meteor shower are very scarce, particularly at low latitudes. In this paper the observational data from Gadanki radar (13.46°N, 79.18°E) have been used to determine the particle size distribution and the number density of meteoroids inside the stream of the Geminid meteor shower. The mean variation of meteor number density across the stream has been determined for three echo duration classes, T<0.4, T=0.4–1 and T>1 s. We are more interested in the appearance of echoes of various durations and therefore meteors of various masses in order to understand more on the filamentary structure of the stream. It is observed that the faint particle flux peaks earlier than the larger particles. We found a decreasing trend in the mass index values from the day of peak activity to the next observation days. The mass index profile was found to be U-shaped with a minimum value near the time of peak activity. The observed minimum s values are 1.64±0.05 and 1.65±0.04 in the years 2003 and 2005, respectively. The activity of the shower indicates the mass segregation of meteoroids inside the stream. Our results are best comparable with the “scissors” structure model of the meteoroid stream formation of Ryabova [2007. Mathematical modeling of the Geminid meteoroid stream. Mon. Not. R. Astron. Soc. 375, 1371–1380] by considering the asteroid 3200 Phaethon as an extinct comet.     

Photographic Observations of the 1996 Leonid Fireballs in Japan

Several Leonid fireballs were successfully photographed by the Japanese Fireball Network and by other observers in Japan on 16 November, 1996. A totals of seven of these were simultaneously observed from two or more stations, from which the orbital and physical data were deduced. The radiant of these fireballs were very small, only 0.1°, similar to that of the 1991 Perseids. The 1996 Leonids showed a lower magnitude distribution index similar to those obtained in the 1961 and 1965 Leonids. All of these showers occurred before perihelion passage of the parent comet. We conclude that we have already encountered the elongated front part of the dust trail of the Leonid parent comet, where the trail is probably composed of larger dust particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radio and Meteor Science Outcomes From Comparisons of Meteor Radar Observations at AMISR Poker Flat, Sondrestrom, and Arecibo

Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.     

A Method for Determining the Coordinates of Meteor Shower Radiants from Meteor Radar Goniometric Data

We discuss a new method for measuring the coordinates of meteor shower radiants from meteor radar data. The method uses a high accuracy of radar goniometer measurements of one of the angular coordinates for meteor radiants and collective properties of incident meteor showers. It is based on a computer technology of searching for the coordinates of radiants using the intersections of meteor position lines on the celestial sphere and filtering nonrandom combinations of these intersections. The method allows the following: to detect meteor showers with a rate of more than 5 per day of observations and to separate meteor groups from different meteor showers with different radiants and velocities. The method makes it possible to increase the angular resolution from 10° × 10° achieved with a quasi-tomographic technique to 2° × 2°, with a prospect of a further increase in the accuracy through the individual reduction of separated meteor groups. We use the reduction of one-day-long observations during maximum activity of the Geminids meteor shower in 1993 to illustrate the potentialities of the method. We show an example of detecting a weak meteor shower that was active during December 1993.     

Meteor Orbit Determinations with Multistatic Receivers Using the MU Radar

The MU radar of RISH (Research Institute for Sustainable Humanosphere, Kyoto University), which is a MST radar (46.5 MHz, 1 MW peak power), has been successfully applied to meteor studies by using its very high versatility. The system has recently renewed with 25 channel digital receivers which significantly improved the sensitivity and precision of interferometer used in meteor observation. The transmission is now synchronized to GPS signals, and two external receiving sites with a ranging capability has additionally been operated in order to determine the trajectories and speeds of meteoroids.     

流星雷达测距精度的改进

针对目前流星雷达测距误差大的问题，本文提出了提高流星雷达测距精度的新方法，即提高采样速率，用相关分析确定回波脉冲参考点的方法。该方法使流星雷达的测距精度提高一个数量级，测距误差降到±１４ｍ，使流星雷达不仅可以用来观测研究流星，还可用于监测飞机、火箭的飞行等，扩大流星雷达的应用。     

Plasma and Electromagnetic Simulations of Meteor Head Echo Radar Reflections

Recently, meteor head echo detections from high powered large aperture radars (HPLA) have brought new measurements to bear on the study of sporadic interplanetary meteors. These same observations have demonstrated an ability to observe smaller meteoroids without some of the geometrical restrictions of specular radar techniques. Yet incorporating data from various radar reflection types and from different radars into a single consistent model has proven challenging. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. In order to overcome some of the unknown relationships between meteoroid characteristics (such as mass and velocity) and the resulting head echo radar cross-sections (RCS), we present our results on meteor plasma simulations of head echo plasmas using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body at speeds as large as several kilometers per second. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross-section of the simulated meteor plasma electron distributions. These simulations have shown that the radar cross-section depends in a complex manner on a number of parameters. In this paper we demonstrate that for a given head echo plasma the RCS as a function of radar frequency peaks at sqrt (2*peak plasma frequency) and then decays linearly on a dB scale with increasing radar frequency. We also demonstrate that for a fixed radar frequency, the RCS increases linearly on a dB scale with increasing head echo plasma frequency. These simulations and resulting characterization of the head echo radar cross-section will both help relate HPLA radar observations to meteoroid properties and aid in determining a particular radar facility’s ability to observe various meteoroid populations.     

用陕西天文台流星雷达监测人为空间碎片可能性的分析

本文分析了利用中国科学院陕西天文台的流星雷达进行人为空间碎片监测的可能性．详细计算了到达接收机的回波的信噪比Ｓ／Ｎ依赖于目标散射横截面。和高度距离Ｒ的关系。理论计算表明，利用陕西天文台的流星雷达完全有可能监测在２００ｋｍ至１２００ｋｍ的高度范围内，半径大于０．５ｍ的人为空间碎片．     

The IAU Meteor Shower Nomenclature Rules

The International Astronomical Union at its 2006 General Assembly in Prague has adopted a set of rules for meteor shower nomenclature, a working list with designated names (with IAU numbers and three-letter codes), and established a Task Group for Meteor Shower Nomenclature in Commission 22 (Meteors and Interplanetary Dust) to help define which meteor showers exist from well defined groups of meteoroids from a single parent body.