首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The effects of 2009 Leonid Meteor Shower upon the two VLF subionospheric transmitted signals and vertical electric potential gradient from the ground surface have been studied from Kolkata (Lat: 22.56°N, Long: 88.5°E) on November 17, 2009. The received signals showed their peak values when ZHR (Zenithal Hourly Rate) was highest. Some typical variations in the outcome of these measurements during the meteor showers will be presented in this paper.  相似文献   

2.
We show that the retrospective evolution method yields excessively large inaccuracies in determining the age of meteorid streams. The cause is in its sensitivity to the errors in the initial conditions. The study was fulfilled with the Geminid, Quadrantid, Orionid, Perseid, and Leonid meteor showers as an example.  相似文献   

3.
The results of day-time detection of GEMINID 2007 meteor shower from dynamic VLF radiation spectra in Tripura (23.50° N, 91.25° E), India, is presented here. The field experiments were performed during 12–17th December, 2007 inside Tripura University campus located at a hilly place in the North-Eastern part of India. A well calibrated software VLF receiver was used to perform the field experiments. Analyses of data reveal an hourly average rate of the shower around 50. The VLF emissions lie in the range from 8 kHz to 13 kHz which is 10 to 15 times higher than previous reports. The mean duration of each VLF emission calculated from dynamic spectra is found to be 6 s and the mean bandwidth is 3.6 kHz. The temporal variation of VLF emission duration and bandwidth of VLF radiation is also studied. The results strongly support the fact that VLF electromagnetic waves are produced during the passage of meteors in the atmosphere. The experiment also makes the study of dynamic VLF spectra as a strong tool to detect low intensity meteor shower during daytime.  相似文献   

4.
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.  相似文献   

5.
Tempel—Tuttle彗星与近年的狮子座流星雨   总被引：1，自引：0，他引：1  
吴光节 《天文学报》2001,42(2):125-133
对狮子座流雨的历史进行了回顾和讨论，并利用“彗星－地球轨道分离（CEOS）及地球滞后彗星时间（TE－C）”统计图进行分析，发现几乎所有的狮子座流星都位于一个倾斜的方框内，而这倾斜方框械右边界的斜率大约为15m/s，方框的宽度大约为4yr，它表明，33年一度的狮子座流星雨一般不会有超过4年的爆发期，更细致的分析表明，最强的流星暴位于一弯曲的细窄条带，在慧星一次回归期，亮流星的比例将年衰减，这些事实，可以用运动，碎裂，扩散和尘埃彗尾模型进行解释，由15m/s速度得到的流星体尺度大小也与事实相容，并且，这表明与地球相遇的流星体粒子是以有限的速度偏离彗星时间（TE－C）就越长，由此倾斜方框的存在，可以对未来狮子座流星雨进行了预报，表明在1998－2000年期间将有较强的狮子座流星雨，中心在1999年，至于2000年以后，要在100多年以后才会有较强的流星暴，而狮子座流星雨的辉煌期可以说已经过去。  相似文献   

6.
The asteroid 3200 Phaethon is suggested as a candidate for direct impact research. The object is considered to be an extinct comet and the parent of the Geminid meteor shower. One could say that this provides a possible argument for a space mission. Based on such a mission, this paper proposes to investigate the nature of the extinct comet and the additional interesting possibility of artificially generated meteor showers.
Dust trail theory can calculate the distribution of a bundle of trails and be used to show in which years artificial meteors would be expected. Results indicate that meteor showers will be seen on Earth about 200 yr after the event, on 2022 April 12.  相似文献   

7.
Abstract— We report spectroscopic observations of meteors made from the FISTA aircraft on 1998 November 17 as a part of the Leonid multi-instrument aircraft campaign. Low-resolution spectra of 119 meteors of apparent visual magnitudes from +3 to ?4, corresponding to meteoroid masses from 10?6 to 10?3 kg, were obtained. After analyzing a representative sample of the spectra and comparing them to the spectra of Perseid meteors from the Ondrejov archive, the following conclusions were reached: Leonid meteoroids are very loose and disintegrate easily in the atmosphere. This leads to much faster evaporation of volatile Na than of other elements, an effect which is not observed in the Perseid meteors. Relative bulk abundances of Mg, Fe, Ca, and Na in Leonid meteors are nearly CI-chondritic within the uncertainty of the method (factor of 3). Smaller meteoroids tend to be poorer in Na, which is true also for Perseid meteors. Most meteoric vapor emissions could be reasonably well explained with the temperature of 4500 K. High-temperature meteoric emissions (Ca+, Mg+) are present only in bright meteors. Leonid spectra are very rich in atmospheric emissions of O, N, and N2, even at high altitudes and in faint meteors. These emissions are therefore not connected with the meteor shock wave. Thermal continuum is also present in the spectra. Organic material was not revealed.  相似文献   

8.
Abstract— We have used a 3.0 m diameter liquid mirror telescope (LMT) coupled to a microchannel plate image‐intensified charge‐coupled device (CCD) detector to study the 1999 Leonid meteor shower. This is the largest aperture optical instrument ever utilized for meteor detection. While the observing system is sensitive down to stars of +18 astronomical magnitude under optimum conditions, when corrections for meteor motion are applied the majority of the meteors collected fall in the absolute magnitude range from +5 to +10, corresponding to photometric masses from about 10?7 to 10?9 kg. This is largely due to the fact that the field of view of the LMT was only 0.28°, so that only a small portion of the luminous meteor trail was recorded. While the flux of these small (1.4 times 10?9 kg) Leonid meteors is low (on the order of one Leonid meteor per hour per square kilometer perpendicular to the Leonid), we do have clear evidence that the Leonid stream contains particles in the mass range studied here. The data showed a possibly significant peak in Leonid flux (9.3 ± 3.5) for the 1 h period from 11:00 to 12:00 u.t. 1999 November 17 (solar longitude 234.653 to 234.695, epoch 2000.0), although the main trend of these results is a broad low‐level Leonid activity. There is evidence that small meteoroids are more widely distributed in the Leonid stream, as would be expected from cometary ejection stream models. As would be expected from an extrapolation of mass distribution indices for brighter meteors, the vast majority of meteors at this size are sporadic. The LMT is a powerful detector of sporadic meteors, with an average non‐Leonid detection rate of more than 140 meteor events per hour.  相似文献   

9.
We have restored and ordered the archive of meteor observations carried out with a meteor radar complex KGU-M5 since 1986. A relational database has been formed under the control of the Database Management System (DBMS) Oracle 8. We also improved and tested a statistical method for studying the fine spatial structure of meteor streams with allowance for the specific features of application of the DBMS. Statistical analysis of the results of observations made it possible to obtain information about the substance distribution in the Quadrantid, Geminid, and Perseid meteor streams.  相似文献   

10.
Every year the Earth crosses or passes near one of the dust trails left by Comet 55P/Tempel-Tuttle in its pass through the Solar System every 33.2 years. This produces a meteor shower Commonly called the Leonid. The 2001 Leonid meteor shower is one of the strongest in recent years. We present observations made by the 50 MHz all-sky meteor radar located at the Platteville Atmospheric Observatory in Colorado (40° N, 105° W). The spatial and temporal distributions of the meteor activity detected by the radar during the 2001 Leonid shower differs from the observed sporadic activity detected by VHF radars. Estimation of the radiant flux of the meteor shower of the shower by a well-known methodology is presented, and the intensity of the phenomena is discussed.  相似文献   

11.
The effect of solar eclipse of July 22, 2009, obscuring up to 91 %, upon the value of point discharge current (PDC) has been reported in this paper. The observation had been taken from Kolkata (Lat. 22.56°N, Long. 88.5°E). During the eclipse period, significant variations in the magnitude of PDC were observed than their average value for the same period in other days. The average value of the PDC for the successive ±10 days adjacent to the solar eclipse day was about 2.253 A.U. (Arbitrary Unit), while the minimum value showed about 2.242 A.U. at the time of greatest phase at 06:26.4 IST (Indian Standard Time). The results are mainly interpreted in terms of changes of the conductivity of the medium during the solar eclipse.  相似文献   

12.
The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25°16′ N, Longitude 82°59′ E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographic latitude 17°20′ N, longitude 78°30′ E) and Bangalore (Geographic latitude 12°58′ N, longitude 77°33′ E) in India. We describe the diurnal and seasonal variations of total electron content (TEC), and the effects of a space weather related event i.e. a geomagnetic storm on TEC. The mean diurnal variation during different seasons is brought out. It is found that TEC at all the three stations is maximum during equinoctial months (March, April, September and October), and minimum during the winter months (November, December, January and February), while obtaining intermediate values during summer months (May, June, July and August). TEC shows a semi-annual variation. TEC variation during geomagnetic quiet as well as disturbed days of each month and hence for each season from May 2007 to April 2008 at Varanasi is examined and is found to be more during disturbed period compared to that in the quiet period. Monthly, seasonal and annual variability of GPS-TEC has been compared with those derived from International Reference Ionosphere (IRI)-2007 with three different options of topside electron density, NeQuick, IRI01-corr and IRI 2001. A good agreement is found between the GPS-TEC and IRI model TEC at all the three stations.  相似文献   

13.
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.  相似文献   

14.
Abstract— We report on studies of the Fe, Ca, and K atom densities in the trails of meteors. The measurements of the densities were taken simultaneously and in a common volume by three ground-based lidars. We report and analyze the data obtained during two nights of Leonid showers (1996 and 1998 November 16/17) and of one night five days after the 1998 Leonids. The lidar-observed trails of Leonids differ from those of other meteor showers in both their mean altitude and in mean metal composition. The Leonid trails show a highly depressed Ca/Fe abundance ratio in comparison to CI meteoritic composition. Our observations are interpreted with the help of a numerical model that describes the ablation processes occurring during the high-speed entry of meteoroids into the Earth's atmosphere. We conclude that for the lidar-observed meteoroids, the ablation process occurs differentially for the three elements. This leads to a mixture of metals in the meteor trails, the composition of which is strongly altitude dependent and at any one altitude deviates significantly from a CI meteoritic composition. The model predicts differing altitudes and durations of trail observations for different showers, allowing us to tentatively assign the origin to the observed trails.  相似文献   

15.
The issue of the presence of meter- and decameter-sized bodies in meteor and fireball streams is of fundamental importance in the context of the theory of disintegration of parent bodies. Our observations, which have been carried out since 1995, indicate that such bodies are present in the Perseid, α-Capricornid, Leonid, and Coma-Berenicid meteoric streams. A catalogue is presented here for the parameters of the detected bodies. The spatial density of the meter-sized bodies is estimated based on the observational material. Within the errors, our estimates agree with the estimates based on the extrapolation of meteor and fireball data. An analysis of the observations suggests some inferences on the structure of the streams under study.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 263–271.Original Russian Text Copyright © 2005 by Barabanov, Smirnov.  相似文献   

16.
We have analysed the meteor records in the chronicles that describe the era of the Song dynasty ( ad 960–1279). The data are complementary to the record-vacant 10th century of the Koryo dynasty ( ad 918–1392). The annual activity of sporadic meteors analysed shows a generic sinusoidal behaviour as in modern observations. In addition, we have also found that there are two prominent meteor showers, one in August and the other in November, appearing on the fluctuating sporadic meteors. The date of occurrence of the August shower indicates it to be the Perseids. By comparing the date of occurrence of the November shower with those of the Leonid showers of the Koryo dynasty, recent visual observations and the world-wide historical meteor storms, we conclude that the November shower is the Leonids. The regression rate of the Leonids is obtained to be     days per century, which agrees with recent observations.  相似文献   

17.
Abstract— In 1996, a broad outburst structure of bright Leonid meteors similar to the 1995 and the 1994 displays (Jenniskens, 1996; Langbroek, 1996b) was observed. In addition, a second narrow outburst structure of fainter meteors, which will be reported and discussed in this paper, has with certainty been observed. This observation marks the first detection of such a narrow structure in the new series of Leonid outbursts. It has a similar exponential activity behaviour and similar emphasis on fainter meteors as shown by the 1866 and 1966 Leonid storm structures. Similar narrow peaks have been observed in 1965 and 1969 (Jenniskens, 1995, 1996). The broad 1996 structure of bright meteors peaked at November 17.31 ± 0.04 (λ 235°.28 ± 0.04 (2000.0)). The additional narrow structure peaked at November 17.20 ± 0.01 (λ 235°.172 ± 0.007). The occurrence of the narrow peak can best be explained as a first modest sign of presence of the meteoroid structure that should be responsible for the expected meteor storm activity of the Leonids in 1998–1999. The appearance 0.°085 before the node of 55P/Tempel-Tuttle suggests that the expected 1998–1999 Leonid storms might peak just before passage through the node of the comet.  相似文献   

18.
We deal with theoretical meteoroid streams the parent bodies of which are two Halley-type comets in orbits situated at a relatively large distance from the orbit of Earth: 126P/1996 P1 and 161P/2004 V2. For two perihelion passages of each comet in the far past, we model the theoretical stream and follow its dynamical evolution until the present. We predict the characteristics of potential meteor showers according to the dynamical properties of theoretical particles currently approaching the orbit of the Earth. Our dynamical study reveals that the comet 161P/2004 V2 could have an associated Earth-observable meteor shower, although no significant number of theoretical particles are identified with real, photographic, video, or radar meteors. However, the mean radiant of the shower is predicted on the southern sky (its declination is about −23°) where a relatively low number of real meteors has been detected and, therefore, recorded in the databases used. The shower of 161P has a compact radiant area and a relatively large geocentric velocity of ∼53 km s−1. A significant fraction of particles assumed to be released from comet 126P also cross the Earth’s orbit and, eventually, could be observed as meteors. However, their radiant area is largely dispersed (declination of radiants spans from about +60° to the south pole) and, therefore, mixed with the sporadic meteor background. An identification with real meteors is practically impossible.  相似文献   

19.
Very Low Frequency (VLF) radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excess or deficient extreme ultra-violet and X-rays, which otherwise sustain the ionosphere, change the waveguide properties and hence the signals are modified. We report the results of monitoring of the NWC transmitter (19.8?kHz) by a receiver placed at Khukurdaha (22°27′N, 87°45′E) during the partial solar eclipse (75?%) of 15th January, 2010. The propagation path from the transmitter to the receiver crosses the annular eclipse belt. We got a clear depression in the data during the period of the eclipse. Most interestingly, there was also a X-ray flaring activity in the sun on that day which reached its peak (C-type) right after the time when the eclipse reached its maximum. We saw the effects of the occultation of this flare in our VLF signal since a part of the X-ray active region was clearly blocked by the moon. We quantitatively compared by using analogies with previous observations and found best fitting parameters for the time when the flare was occulted. We then reconstructed the VLF signal in the absence of the occulted flare. To our knowledge, this is the first such incident where the solar flare was observed through lunar occultation and that too during a partial eclipse.  相似文献   

20.
Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures in persistent trains have been measured by atmospheric O2 A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated a temperature of ∼ ∼130 K as a final exothermic temperature at early stage of persistent trains.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号