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11.
Werner Singer Ralph Latteck Luis Federico Millan Nick J. Mitchell Jens Fiedler 《Earth, Moon, and Planets》2008,102(1-4):403-409
Many meteoroids burn up between about 120 km and 70 km, deposit metals and dust and form ionized trails which are detected
by radars. Model studies about the influence of neutral or positively charged background dust on the ambipolar diffusion indicate
that significant smaller decay times should be observed for weak meteor echoes compared to strong meteor echoes which can
affect the estimation of temperatures. The variation of meteor decay times in dependence on echo strength, height, and season
was studied using radar observations at 69° N, 22° S, and 67° S. Significantly reduced decay times were found for weak echoes
below about 88 km at low latitudes throughout the year, and at high latitudes with the exception of summer. In summer at high
latitudes, decreasing decay times of weak and strong meteors are observed at altitudes below about 85 km during the appearance
of noctilucent clouds. The impact of reduced decay times on the estimation of neutral temperatures from decay times is discussed. 相似文献
12.
Peter S. Gural 《Earth, Moon, and Planets》2008,102(1-4):269-275
An ever increasing variety of electronic instrumentation is being brought to bear in meteor studies and analysis, with unique
meteor detection challenges arising from the attempt to do automated and near real-time processing of the imagery. Recent
algorithm developments in the literature have been applied and implemented in software to provide reliable meteor detection
in all-sky imagers, wide-field intensified video, and narrow field-of-view telescopic systems. The algorithms that have been
employed for meteor streak detection include Hough transforms with phase coded disk, localized Hough transforms with matched
filtering, and fast moving cluster detection. They have found application in identifying meteor tracks in the Spanish Fireball
Network all-sky images, detailed analysis of video recordings during the recent Leonid meteor storms, and development of a
detection/cueing technology system for rapid slew and tracking of meteors. 相似文献
13.
M. Hajduková Jr. 《Earth, Moon, and Planets》2008,102(1-4):67-71
The hyperbolic meteor orbits among the 4,581 photographic and 62,906 radar meteors of the IAU MDC have been analysed using
statistical methods. It was shown that the vast majority of hyperbolic orbits has been caused by the dispersion of determined
velocities. The large proportion of hyperbolic orbits among the known meteor showers strongly suggests the hyperbolicity of
the meteors is not real. The number of apparent hyperbolic orbits increases inversely proportional to the difference between
the mean heliocentric velocity of meteor shower and the parabolic velocity limit. The number of hyperbolic meteors in the
investigated catalogues does not, in any case, represent the number of interstellar meteors in observational data. The apparent
hyperbolicity of these orbits is caused by a high spread in velocity determination, shifting a part of the data through the
parabolic limit. 相似文献
14.
Armagh Observatory installed a sky monitoring system consisting of two wide angle (90° × 52°) and one medium angle (52° × 35°)
cameras in July 2005. The medium angle camera is part of a double station setup with a similar camera in Bangor, ∼73 km ENE
of Armagh. All cameras use UFOCapture to record meteors automatically; software for off-line photometry, astrometry and double
station calculations is currently being developed. The specifications of the cameras and cluster configuration are described
in detail. 2425 single station meteors (1167, 861 and 806 by the medium-angle and the wide-angle cameras respectively) and
547 double station meteors were recorded during the months July 2005 to Dec 2006. About 212 double station meteors were recorded
by more than one camera in the cluster. The effects of weather conditions on camera productivity are discussed. The distribution
of single and double station meteor counts observed for the years 2005 and 2006 and calibrated for weather conditions are
presented. 相似文献
15.
P.B. Babadzhanov 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):221-234
Recent theoretical and observational work has shown that the asteroids belonging to the Taurid meteoroid complex have a cometary
nature. If so, then they might possess related meteoroid streams producing meteor showers in the Earth atmosphere. We studied
the orbital evolution of ten numbered Taurid complex asteroids by the Halphen-Goryachev method. It turned out that all of
these asteroids are quadruple crossers relative to the Earth's orbit. Therefore their proposed meteoroid streams may in theory
each produce four meteor showers. The theoretical orbital elements and geocentric radiants of these showers are determined
and compared with the available observational data. The existence of the predicted forty meteor showers of the ten Taurid
complex asteroids is confirmed by a search of the published catalogues of observed meteor shower radiants and orbits, and
of the archives of the IAU Meteor Data Center (Lund). The existence of meteor showers associated with the Taurid Complex Asteroids
confirms that, most likely, these asteroids are extinct comets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Yang Kejun 《时间频率学报》1995,(1)
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. 相似文献
17.
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。 相似文献
18.
This paper describes the Canadian Meteor Orbit Radar (CMOR) that has been in operation since late 2001. CMOR is a 3 station meteor radar operating at a frequency of 29.85 MHz near Tavistock, Ont. To avoid bias against fragmenting meteoroids that is inherent in the traditional multi-station method of Gill and Davies (Mon. Not. R Astron. Soc. 116 (1955) 105), we use a completely geometrical method similar to that used in the AMOR system (Quart. J. R. Astron. Soc. 35 (1994) 293) based on the interferometric determination of the echo directions and the time delays of echoes from two remote stations to obtain the trajectories and speeds of meteoroids. We describe the hardware and some of the software and present some preliminary results that provide a good indication of present capabilities of the system. Typically, we can measure 1500 individual trajectories, and hence orbits, per day with a mean accuracy of 6° in direction and about 10% in speed. A small subset of these for which it is possible to measure the speeds using Hocking's (Radio. Sci. 35 (2000) 1205) method yield speeds with a precision of about 5%. The purpose of this paper is to show that the radiants and speeds necessary for the computation of orbits are well measured rather than to discuss any orbital surveys. 相似文献
19.
Probabilities of Perception and Population Index in Visual Observations of Meteor Showers 总被引:2,自引:0,他引:2
Earth, Moon, and Planets - 相似文献
20.
J. Du W.E. Ward J. Oberheide T. Nakamura T. Tsuda 《Journal of Atmospheric and Solar》2007,69(17-18):2159
The extended Canadian Middle Atmosphere Model (extended CMAM) is a general circulation model, which extends from the surface to about 210 km. Spatial complex spectral analysis is applied to horizontal winds simulated by the extended CMAM to obtain semidiurnal tidal amplitudes and phases (from e5 to w5) in the mesosphere and lower thermosphere (MLT) region. The dominant w2 migrating component and the presence of eight nonmigrating tides (w3, w4, w5, e1, e2, e3, e4 and e5) in the mid-latitudes are identified. Components w1 and s0, which tend to maximize at high latitudes, will be discussed separately in a later paper. The migrating semidiurnal tide (w2) has amplitudes reaching over 20 m s−1 for both zonal and meridional winds in the mid-latitude region. Its form compares well to the published results. The amplitudes of nonmigrating semidiurnal tides are non-negligible compared with the migrating semidiurnal tides. The amplitudes for w3 and e2 exceed 12 and 8 m s−1, respectively.Comparisons are made with four nonmigrating semidiurnal components (w3, w4, e1 and e2) derived from the TIMED Doppler interferometer (TIDI) wind measurements between 85 and 105 km altitude and between 45°S and 45°N latitude. Overall, the basic CMAM and TIDI latitudinal structures of the amplitudes agree well and the agreement between the annual mean amplitudes varies with component. Relative to the TIDI results, the CMAM seasonal variations of w4 are in good agreement, of e2 are in reasonable agreement, of w3 are in partial agreement and of e1 are in poor agreement.The 11 semidiurnal components from the model are superimposed to generate the total semidiurnal winds at Jakarta (6°S, 106°E) and Kototabang (0°, 100°E) and are compared with measurements from two equatorial meteor radar stations at these sites. The relative contributions of components to the reconstructed amplitude vary from month to month. The CMAM reconstructions are generally larger than the radar results by a factor varying between one and two. The phases in the radar data are typically stationary with respect to height, whereas they generally decrease with height in the CMAM reconstruction. 相似文献