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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
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Csilla Szasz Johan Kero Asta Pellinen-Wannberg David D. Meisel Gudmund Wannberg Assar Westman 《Earth, Moon, and Planets》2008,102(1-4):373-378
We have investigated the conditions for simultaneous meteor observations with the EISCAT UHF radar system and telescopic optical
devices. The observed characteristics of 410 meteors detected by all three UHF receivers are compared with model simulations
and their luminosity is calculated as a part of a meteoroid ablation model using a fifth order Runge–Kutta numerical integration
technique. The estimated absolute visual magnitudes are in the range of +9 to +5. The meteors should therefore be observable
using intensified CCD or EMCCD (Electron Multiplying CCD) cameras with telephoto lenses. A possible setup of a coordinated
radar and optical campaign is suggested. 相似文献
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The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height
range of 80–140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere
properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over
the mass range 10−16 kg to 10−7 kg, but the faint end of this range cannot be observed by any other method and so direct verification is not possible. On
the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations
can be fit to a “standard” ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the features
of the ab initio model that are different from the “standard” model are: (1) uses the experimentally based low pressure vaporization
theory of O’Hanlon (A users’s guide to vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from
experimental data on heat transfer, luminosity and ionization efficiencies measured by Friichtenicht and Becker (NASA Special
Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids
and ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses
a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits
(as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC
Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical
Quantities 2000). This utilization of mostly experimentally determined data is the main reason for calling this an ab initio
model and is made necessary by the fact that individual average meteoroid mass densities are now derivable from Arecibo observations. 相似文献
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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
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Gbor Timr Balzs Szkely Gbor Molnr Csaba Ferencz Anik Kern Csilla Galambos Gbor Gercsk Lszl Zentai 《Global and Planetary Change》2008,62(1-2):29-38
The area of Banat, a historical region shared by Romania and Serbia, has been hit by a centennial flood event in spring 2005. The Temes (Tamiš/Timiş) River flooded several hundred km2, with many settlements. The extent of the flood was partly unexpected, especially in positional sense. In order to achieve a better understanding of the phenomenon, we analysed the SRTM digital elevation model as well as historical maps. Several historical maps, dating back to the 16th century, indicate marshland or even a large lake in the area, not existing today but almost exactly coinciding with the extent of the 2005 flood.The historical and archive maps document the water regulation measures taken since the early 19th century. The actual flood is found to be a sort of a restoration of the original natural conditions. Via the analysis of the DEM and historical maps the unexpected extent of the flood scenario can be explained and understood. We suggest that an analysis of historical and archive maps, combined (geo-referenced) with high-resolution DEMS in other flood-endangered areas, should be used in order to be better prepared for decadal or centennial flood events induced by climatic change. 相似文献
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Róbert Mészáros ádám Leel?ssy Csilla Vincze Mihály Sz?cs Tibor Kovács István Lagzi 《Theoretical and Applied Climatology》2012,107(3-4):375-387
We investigate the influence of the regional-scale weather types on the atmospheric dispersion processes of the air pollutants originated from point sources. Hypothetical accidents were simulated with two different dispersion models. During a year’s test period, the 6-h emission of a radionuclide from the Paks Nuclear Power Plant (Paks NPP, Hungary) was assumed every day and the transport and deposition of the radionuclide was simulated by the Eulerian TREX dispersion model over the Central European region. In addition, the ALOHA Gaussian air dispersion model was also used for the local environment of the Paks NPP to simulate hypothetical hourly releases of ammonia during a 10-year period. During both types of model simulations, the dispersion of the plume for each time was analysed and tested with consideration of 13 circulation types corresponding to daily weather patterns over the Carpathian Basin. There are significant correlations between circulation types and plume directions and structures both in local and regional scales. The daily circulation pattern can be easily obtained from weather analyses; the expected size and direction of polluted area after an accidental release can be quickly estimated even before an accident occurs. However, this fast method cannot replace or neglect dispersion model simulations. It gives a ‘first guess’ and a fast estimation on the direction of the plume and can provide sufficient information for decision-making strategies. 相似文献
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C. Szasz J. Kero D. D. Meisel A. Pellinen-Wannberg G. Wannberg A. Westman 《Monthly notices of the Royal Astronomical Society》2008,388(1):15-25
The tristatic EISCAT 930-MHz UHF system is used to determine the absolute geocentric velocities of meteors detected with all three receivers simultaneously at 96 km, the height of the common radar volume. The data used in this study were taken between 2002 and 2005, during four 24-h runs at summer/winter solstice and vernal/autumnal equinox to observe the largest seasonal difference. The observed velocities of 410 tristatic meteors are integrated back through the Earth atmosphere to find their atmospheric entry velocities using an ablation model. Orbit calculations are performed by taking zenith attraction, Earth rotation as well as obliquity of the ecliptic into account. The results are presented in the form of different orbital characteristics. None of the observed meteors appears to be of extrasolar or asteroidal origin; comets, particularly short-period (<200 yr) ones, may be the dominant source for the particles observed. About 40 per cent of the radiants can be associated with the north apex sporadic meteor source and 58 per cent of the orbits are retrograde. There is evidence of resonance gaps at semimajor axis values corresponding to commensurabilities with Jupiter, which may be the first convincing evidence of Jupiter's gravitational influence on the population of small sporadic meteoroids surveyed by radar. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km s−1 and a retrograde population peaking at 59 km s−1 . The EISCAT radar system is located close to the Arctic Circle, which means that the North Ecliptic Pole (NEP) is near zenith once every 24 h, i.e. during each observational period. In this particular geometry, the local horizon coincides with the ecliptic plane. The meteoroid influx should therefore be directly comparable throughout the year. 相似文献
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Johan Kero Csilla Szasz Asta Pellinen-Wannberg Gudmund Wannberg Assar Westman 《Earth, Moon, and Planets》2004,95(1-4):633-638
We present observations and preliminary results from a meteor experiment carried out with the 224 MHz EISCAT VHF radar in Tromsø, Norway, which was run for 6 h on November 26, 2003. The data set contains echoes with peculiar pulsations in received power in the frequency range 20–200 Hz, limited by instrumental parameters. The process causing the echo power pulsations has not yet been identified. Plasma effects are the most likely cause, a possible mechanism is for instance asymmetrical dust grains in rotation causing a modulation of the ionization rate. 相似文献
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Simionescu's (1899) inoceramid material from the topmost Turonian/Lower Coniacian of Ürmös (Ormenis), Transylvania, Romania contains ten species which are for the first time photographically illustrated. Of four new forms described by Simionescu (1899a), three referred here toMytiloides carpathicus(Simionescu),Cremnoceramus globosus(Simionescu), andC. transilvanicus(Simionescu), represent valid species. The type of the fourth species,Inoceramus kilianiSimionesu, represents a deformed specimen of an undetermined Late Turonian mytiloid, while the name is formally a junior synonym ofVolviceramus involutus(J. de C. Sowerby). The assemblage is time equivalent of the inoceramid association described from the Krebitz-Zittauer (Saxony, Germany) Cretaceous by Andert (1911) but, contrary to suggestions of Heinz (1930), the forms described by Andert and Simionescu are not conspecific. 相似文献