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1.
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. 相似文献
2.
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
3.
Mykola I. Pishkalo 《Solar physics》2006,233(2):277-290
We have investigated the correlation between the relative sunspot number and tilt of the heliospheric current sheet (HCS)
in solar cycles 21–23. Strong and highly significant positive correlation (r > 0.8, P < 0.001) was found for corresponding data in the time interval from May 1976 through December 2004. Cross-correlation analysis
does not reveal any time shift between the data sets. Reconstructed values of the HCS tilt, for the time interval before 1976,
are found using sunspot numbers. To take different amplitude of solar cycles into account they were then normalized to zero
in the minima of the solar activity and to average in solar cycles 21–23 maximal calculated HCS tilt in the maxima. These
normalized reconstructed HCS data are compared with the angular positions of the brightest coronal streamers observed during
total solar eclipses in 1870–2002, and their agreement is better for the minima of the solar activity than for the maxima. 相似文献
4.
Devulapalli Venkata Phani Kumar Kammadhanam Chenna Reddy Ganji Yellaiah 《Astrophysics and Space Science》2006,306(4):235-239
Observations carried out during Leonid meteor shower 2003, by using Indian MST radar (13.46^N, 79.18^E; dip 12.5^N) are used
to determine the number density of meteoroids through the cross section of the meteor streams. Cross sections are calculated
for a number of classes of echo duration (particle size). They are also used to determine the relative flux of the shower
in particle size ranges producing radar meteor echoes having durations <0.4 s, 0.4–1 s and >1 s. Mean activity profiles along
the Earth's passage through the stream show a systematic change of the peak activity and the width of the stream depending
on the distribution of echo durations across the stream. The patterns of mass distribution index s are presented and discussed. 相似文献
5.
Efforts to link minor meteor showers to their parent bodies have been hampered both by the lack of high-accuracy orbits for
weak showers and the incompleteness of our sample of potential parent bodies. The Canadian Meteor Orbital Radar (CMOR) has
accumulated over one million meteor orbits. From this large data set, the existence of weak showers and the accuracy of the
mean orbits of these showers can be improved. The ever-growing catalogue of near-Earth asteroids (NEAs) provides the complimentary
data set for the linking procedure. By combining a detailed examination of the background of sporadic meteors near the orbit
in question (which the radar data makes possible) and by computing the statistical significance of any shower association
(which the improved NEA sample allows) any proposed shower–parent link can be tested much more thoroughly than in the past.
Additional evidence for the links is provided by a single-station meteor radar at the CMOR site which can be used to dispel
confusion between very weak showers and statistical fluctuations in the sporadic background. The use of these techniques and
data sets in concert will allow us to confidently link some weak streams to their parent bodies on a statistical basis, while
at the same time showing that previously identified minor showers have little or no activity and that some previously suggested
linkages may simply be chance alignments. 相似文献
6.
Ohtsuka Katsuhito Shimoda Chikara Yoshikawa Makoto Watanabe Jun-Ichi 《Earth, Moon, and Planets》1997,77(2):83-91
The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear.
Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile
of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude
(J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of
2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type
asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids :
Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon,
we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams
are really associated with Phaethon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Peter Brown Robert J. Weryk Daniel K. Wong James Jones 《Earth, Moon, and Planets》2008,102(1-4):209-219
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. 相似文献
8.
The IAU Meteor Data Center in Lund has acted as a central depository for meteor orbits obtained by photographic, video and
radar techniques. The database of precisely reduced photographic meteors contains data on 4581 meteor orbits obtained by 17
different stations or groups in the period 1936–1996. The orbital and geophysical data are available in two separate files
as well as in an alternative file with the merged data. In various studies of meteoroid streams as well as in studies of the
sporadic meteor background, it is often necessary to utilize both the orbital and the geophysical data files. Since the database
is a compilation of partial, not perfectly compatible catalogues from many observing stations, the merging of parameters from
one data set to another may sometimes present problems. The present contribution is a note on some problems encountered in
the merging procedure. Moreover, it is evident that the database includes a small amount of erroneous data – either in the
observations or in the subsequent data reductions. The latter error is not surprising in view of the lack of modern computers
at several stations in the past. A final, corrected version of the IAU MDC Lund photographic meteor orbits (eq. 2000.0) can
now be requested through the homepage of the Astronomical Institute, Slovak Academy of Sciences (http://www.astro.sk/~ne/IAUMDC/Ph2003/database.html). 相似文献
9.
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. 相似文献
10.
We present the results of a study of meteoroid bulk densities determined from meteor head echoes observed by radar. Meteor
observations were made using the Advanced Research Projects Agency Long-Range Tracking And Instrumentation Radar (ALTAIR).
ALTAIR is particularly well suited to the detection of meteor head echoes, being capable of detecting upwards of 1000 meteor
head echoes per hour. Data were collected for 19 beam pointings and are comprised of approximately 70 min. of VHF observations.
During these observations the ALTAIR beam was directed largely at the north apex sporadic source. Densities are calculated
using the classical physical theory of meteors. Meteoroid masses are determined by applying a full wave scattering theory
to the observed radar cross-section. Observed meteoroids are predominantly in the 10−10 to 10−6 kg mass range. We find that the vast majority of meteoroid densities are consistent with low density, highly porous objects
as would be expected from cometary sources. The median calculated bulk density was found to be 900 kg/m3. The orbital distribution of this population of meteoroids was found to be highly inclined. 相似文献
11.
J. D. Mathews S. J. Briczinski D. D. Meisel C. J. Heinselman 《Earth, Moon, and Planets》2008,102(1-4):365-372
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. 相似文献
12.
We present the first clear observations of meteor shower activity from meteor-head echoes detected by a high-power large-aperture radar (HPLAR). Such observations have been performed at the Jicamarca VHF radar using its interferometric capabilities allowing the discrimination of meteor shower echoes from the much more frequent sporadic meteors. Until now, HPLARs were unable to distinguish meteor shower from the much more common sporadic meteor ones. In this work we have been able to detect and characterize the η-Aquariids (ETA) as well as the Perseids (PER) showers. The shower activity is more conspicuous for the ETA than for the PER shower due to the more favorable geometry. Namely, PER meteors come from low elevation angles, experiencing more filtering due to the combined Earth-atmosphere-radar instrument. In both cases, there is an excellent agreement between the measured mean velocity of the shower echoes and their expected velocity, within a fraction of 1 km s−1. Besides the good agreement with expected visual results, HPLARs observe meteors with a variety of particles sizes and masses, not observed by any other technique. Taking into account the different viewing volumes, compare to optical observations Jicamarca observes more than 1000 times more ETA meteors. Our results indicate that Jicamarca and other HPLARs are able to detect the echoes from meteor showers, but without interferometric capabilities such populations are difficult to identify just from their velocity distributions, particularly if their velocity distributions are expected to be similar to the more dominant distributions of sporadic meteors. 相似文献
13.
Csilla Szasz Johan Kero Asta Pellinen-Wannberg John D. Mathews Nick J. Mitchell Werner Singer 《Earth, Moon, and Planets》2004,95(1-4):101-107
The presence of a diurnal variation in meteor activity is well established. The sporadic meteor count rates are higher on
the local dawn side and lower on the local dusk side. This phenomenon is caused by the Earth’s orbital motion and rotation.
Meteor radar measurements have been compared from Esrange, Kiruna, Sweden, at 68° N, from Juliusruh, Germany, at 55° N, and
from Ascension Island, at 8° S, to investigate how the diurnal variation depends on season at different latitudes. Data have
been used from vernal and autumnal equinoxes and summer and winter solstices to locate the largest seasonal differences. 相似文献
14.
Josep M. Trigo-Rodriguez José M. Madiedo Peter S. Gural Alberto J. Castro-Tirado Jordi Llorca Juan Fabregat Standa Vítek Pep Pujols 《Earth, Moon, and Planets》2008,102(1-4):231-240
By using high-resolution, low-scan-rate, all-sky CCD cameras, the SPanish Meteor Network (SPMN) is currently monitoring meteor
and fireball activity on a year round basis. Here are presented just a sampling of the accurate trajectory, radiant and orbital
data obtained for meteors imaged simultaneously from two SPMN stations during the continuous 2006–2007 coverage of meteor
and fireball monitoring. Typical astrometric uncertainty is 1–2 arc min, while velocity determination errors are of the order
of 0.1–0.5 km/s, which is dependent on the distance of each event to the station and its particular viewing geometry. The
cameras have demonstrated excellent performance for detecting meteor outbursts. The recent development of automatic detection
software is also providing real-time information on the global meteor activity. Finally, some examples of the all-sky CCD
cameras applications for detecting unexpected meteor activity are given. 相似文献
15.
Meteor radar observations of ionized trails in the Earth’s atmosphere provide observations that do not depend on weather conditions
and time of day and provide good statistics for analysis. Further development in the new quasitomographic analysis of the
goniometric data of the Kazan meteoric radar has revealed a number of very weak meteoric streams with rates of more than 5–6
meteors per day. In addition to the known large meteor showers, we have found up to as many as 1000 small showers per month
that we have named microshowers. We shall operationally define a microshower as the minimal meteoric stream which can be detected
with the Kazan meteoric radar while quasitomographic procedures of processing interferometer data are used. 相似文献
16.
Lars P. Dyrud Kelly Denney Julio Urbina Diego Janches Erhan Kudeki Steve Franke 《Earth, Moon, and Planets》2004,95(1-4):89-100
In this paper, we use radar observations from a 50 MHz radar stationed near Salinas, Puerto Rico, to study the variability
of specular as well as non-specular meteor trails in the E-region ionosphere. The observations were made from 18:00 to 08:00 h
AST over various days in 1998 and 1999 during the Coqui II Campaign [Urbina et al., 2000, Geophys. Rev. Lett. 27, 2853–2856]. The radar system had two sub-arrays, both produced beams pointed to the north in the magnetic meridian plane,
perpendicular to the magnetic field, at an elevation angle of approximately 41 degrees.
The Coqui II radar is sensitive to at least two types of echoes from meteor trails: (1) Specular reflections from trails oriented
perpendicular to the radar beam, and (2) scattering, or, non-specular reflections, from trails deposited with arbitrary orientations.
We examine and compare the diurnal and seasonal variability of echoes from specular and non-specular returns observed with
the Coqui II radar. We also compare these results with meteor head echo observations made with the Arecibo 430 MHz radar.
We use common region observations of these three types of meteor echoes to show that the diurnal and seasonal variability
of specular trails, non-specular trails, and head echoes are not equivalent. The implications of these results on global meteor
mass flux estimates obtained from specular meteor observations remains to be examined. 相似文献
17.
David D. Meisel Johan Kero Csilla Szasz Vladimir Sidorov Stan Briczinski 《Earth, Moon, and Planets》2008,102(1-4):315-322
In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number
of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of
true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single
beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with
simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity
as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position
and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been
kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from
the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative
scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source
areas where it is easiest to detect discrete showers with less confusion from the background. 相似文献
18.
The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and
total number and total area of sunspots over the period of 1939 – 2001. Typical time variations of the N – S asymmetry are
found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S
asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices
than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry
of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that
the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the
N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar
activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory
of solar activity is constructed. 相似文献
19.
The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more
than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line
brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within
the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions
between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct
quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived
only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity
of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and
coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity
is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in
fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2
months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed
as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation
in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed
by numerical tests performed by selecting different numerical values of the used parameters. 相似文献
20.
O. I. Evdokimov T. K. Filimonova V. V. Sidorov Rasim Amer Ali 《Earth, Moon, and Planets》1995,68(1-3):267-275
This article contains the tomographic problem's solution of the radiants distribution study by the meteor radar data. It was received the distribution of meteors velocities for the parts of celestial sphere with angular dimensions 10° × 10° and 1° × 1°. Was shown that the angular dimensions of most of radiants are equal 1° – 3° and larger part of the sporadic background looks like a totality of microstreams. 相似文献