Bibliografie tematiche / Meteoroid stream

Letteratura scientifica selezionata sul tema "Meteoroid stream"

Autore: Grafiati

Pubblicato: 8 giugno 2024

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Articoli di riviste sul tema "Meteoroid stream":

Wiliams, I. P. "The Dynamics of Meteoroid Streams". Symposium - International Astronomical Union 152 (1992): 299–313. http://dx.doi.org/10.1017/s0074180900091312.

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Meteor showers are seen at regular and frequent intervals on Earth. They are caused by meteoroids (that is small dust grains) in a coherent stream, all moving on similar heliocentric orbits, burning up on encountering the atmosphere of the Earth. Such streams contain 1012 or more meteoroids, with the mass of the visible meteoroids ranging up to about 1 g. The main evolutionary effect on such streams is gravitational perturbations by the planets. Though grain-grain collision may be catastrophic for the two grains involved, it has no effect on the remainder of the stream, other than the fact that there are now two less grains in it. Solar radiation has some effect, but this can be included in the equations of motion. Because of the large numbers of particles involved, meteoroid streams represent a laboratory where many of our dynamical concepts can be tested.At a basic level, meteoroid streams represent a collective dynamical phenomenon in which all members display roughly the same behavior. One of the fundamental questions which can be investigated is whether the behavior of the mean orbit of the whole stream represents the mean behavior of the stream members. Within the boundaries of some meteor streams lie regions where the orbits are in high order resonance with Jupiter. This also represents a phenomenon of interest. Finally, the possibility exists that some streams are in chaotic regions and it is interesting to investigate whether or not meteoroids in such regions do display chaotic behavior.

Kokhirova, G. I., e P. B. Babadzhanov. "Current Knowledge of Objects Approaching the Earth". Астрономический вестник 57, n. 5 (1 settembre 2023): 458–78. http://dx.doi.org/10.31857/s0320930x23050031.

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Modern ideas about objects approaching the Earth are discussed. This population includes near-Earth asteroids (NEAs), including potentially hazardous asteroids, short-period comets, meteoroid streams, and large sporadic meteoroids. An overview is given of the currently available information on the dynamic and physical properties of NEAs and comets. Almost 5% of the currently known NEAs are extinct cometary nuclei or their fragments. Being outwardly similar with true asteroids, they differ markedly in their dynamic and physical properties. In order to distinguish between these groups of objects, it is necessary to study both their dynamic and physical parameters. Some of the known meteoroid streams are shown to contain, along with the countless small meteoroids, also large extinct fragments of cometary nuclei, which are classified as NEAs. A meteoroid stream and such bodies belonging to it form together an asteroid–meteoroid complex. Observational and theoretical data are presented to confirm the modern understanding of near-Earth objects.

Cukier, W. Z., e J. R. Szalay. "Formation, Structure, and Detectability of the Geminids Meteoroid Stream". Planetary Science Journal 4, n. 6 (1 giugno 2023): 109. http://dx.doi.org/10.3847/psj/acd538.

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Abstract The Geminids meteoroid stream produces one of the most intense meteor showers at Earth. It is an unusual stream in that its parent body is understood to be an asteroid, (3200) Phaethon, unlike most streams, which are formed via ongoing cometary activity. Until recently, our primary understanding of this stream came from Earth-based measurements of the Geminids meteor shower. However, the Parker Solar Probe (PSP) spacecraft has transited near the core of the stream close to its perihelion and provides a new platform to better understand this unique stream. Here, we create a dynamical model of the Geminids meteoroid stream, calibrate its total density to Earth-based measurements, and compare this model to recent observations of the dust environment near the Sun by PSP. For the formation mechanisms considered, we find with the exception of very near perihelion the core of the meteoroid stream predominantly lies interior to the orbit of its parent body and we expect grains in the stream to be ≳10 μm in radius. Data–model comparisons of the location of the stream relative to Phaethon’s orbit near perihelion are more consistent with a catastrophic formation scenario, with the core stream residing near or outside the orbit of its parent body consistent with PSP observations. This is in contrast to a cometary formation mechanism, where even near the Sun the meteoroid stream is interior to the orbit of its parent body. Finally, while PSP transits very near the core of the stream, the impact rate expected from Geminids meteoroids is orders of magnitude below the impact rates observed by PSP, and hence undetectable in situ. We similarly expect the upcoming DESTINY+ mission to be unable to detect appreciable quantities of Geminids grains far from (3200) Phaethon.

Ryabova, Galina O. "Averaged changes in the orbital elements of meteoroids due to Yarkovsky-Radzievskij force". Proceedings of the International Astronomical Union 9, S310 (luglio 2014): 160–61. http://dx.doi.org/10.1017/s1743921314008114.

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AbstractYarkovsky-Radzievskij effect exceeds the Poynting-Robertson effect in the perturbing action on particles larger than 100 μm. We obtained formulae for averaged changes in a meteoroid's Keplerian orbital elements and used them to estimate dispersion in the Geminid meteoroid stream. It was found that dispersion in semi-major axis of the model shower increased nearly three times on condition that meteoroids rotation is fast, and the rotation axis is stable.

Rudawska, Regina, e Tadeusz J. Jopek. "Study of meteoroid stream identification methods". Proceedings of the International Astronomical Union 5, S263 (agosto 2009): 253–56. http://dx.doi.org/10.1017/s1743921310001870.

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AbstractWe have tested the reliability of various meteoroid streams identification methods. We used a numerically generated set of meteoroid orbits (a stream component and a sporadic background) that were searched for streams using several methods.

Moorhead, Althea V., Tiffany D. Clements e Denis Vida. "Realistic gravitational focusing of meteoroid streams". Monthly Notices of the Royal Astronomical Society 494, n. 2 (17 marzo 2020): 2982–94. http://dx.doi.org/10.1093/mnras/staa719.

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ABSTRACT The number density and flux of a meteoroid stream is enhanced near a massive body due to the phenomenon known as gravitational focusing. The greatest enhancement occurs directly opposite the massive body from the stream radiant: as an observer approaches this location, the degree of focusing is unbound for a perfectly collimated stream. However, real meteoroid streams exhibit some dispersion in radiant and speed that will act to eliminate this singularity. In this paper, we derive an analytic approximation for this smoothing that can be used in meteoroid environment models and is based on real measurements of meteor shower radiant dispersion.

Wu, Zidian, e Iwan P. Williams. "The Quadrantid Stream, Chaos or Not?" Symposium - International Astronomical Union 152 (1992): 329–32. http://dx.doi.org/10.1017/s0074180900091348.

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The Quadrantid stream covers a region of space which contains many strong resonances and commensurabilities with the Jovian orbit. We have numerically integrated the orbital evolution of over one hundred actual meteoroids backwards to BC 5000. The evolution is quit complex, but most of the meteoroids are quite well behaved with rapid but smooth changes in the orbital elements. One meteoroid however shows sharp sudden changes in its orbital parameters and these changes are generally indicative of the presence of chaos.

Babadzhanov, P. B., e Yu V. Obrubov. "Dynamics and Spatial Shape of Short-Period Meteoroid Streams". Highlights of Astronomy 8 (1989): 287–93. http://dx.doi.org/10.1017/s1539299600007905.

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AbstractAt the early stage of evolution the meteoroid streams may be considered as elliptical rings of relatively small thickness. The influence of planetary perturbations can essentially increase the stream width and its thickness. As a result one stream may produce several couples of meteor showers active in different seasons of the year. 22 short-period meteoroid streams under review may theoretically produce 104 meteor showers. The existence of 67 is confirmed by observations.

Froeschlé, CL, T. J. Jopek e G. B. Valsecchi. "The Use of Geocentric Variables to Search for Meteoroid Streams and Their Parents". International Astronomical Union Colloquium 172 (1999): 55–64. http://dx.doi.org/10.1017/s0252921100072419.

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AbstractA set of geocentric variables suitable for the identification of meteoroid streams has been recently proposed and successfully applied to photographic meteor orbits. We describe these variables and the secular invariance of some of them, and discuss their use to improve the search for meteoroid stream parents.

А.К., Терентьева,, e Барабанов, С.И. "Meteorite Križevci (Croatia) and meteoroid stream Cancrid". Научные труды Института астрономии РАН, n. 4 (16 dicembre 2022): 241–43. http://dx.doi.org/10.51194/inasan.2022.7.4.004.

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На основании анализа более 500 орбит метеороидных и болидных роев по опубликованным каталогам нами была установлена связь метеорита Križevci, порожденного болидом 4 февраля 2011 г. над Хорватией [1] с метеороидным роем Канкрид (No. 166 (а), [2, 3]). Известный критерий Саутворта-Хокинса дает величину D SH = 0.128, которая является вполне приемлемой для достаточно хорошего согласия орбит метеорита и роя. Динамический параметр Тиссерана указывает на астероидное происхождение роя и метеорита. Таким образом, выявлен еще один метеоритообразующий рой, который дополняет список 14 метеоритообразующих роев, найденных нами ранее [4]. Эти рои имеют важное значение с точки зрения потенциальной опасности при встрече их с Землей. В работе приводится краткая информация о таком редком явлении, которое названо А. Брезиной [5] «цепным падением» метеоритов. Based on the analysis of more than 500 orbits of meteoroid and reball streams according to published catalogs, we established the connection of the Križevci meteorite generated by the bolide on February 4, 2011 over Croatia [1] with a meteoroid stream Cancrid (No. 166 (a), [2, 3]). The well-known Southworth-Hawkins criterion gives a value of D SH = 0.128, which is quite acceptable for a fairly good agreement of the orbits of the meteorite and the stream. The dynamic parameter of Tisserand indicates the asteroid origin of the stream and the meteorite. Thus, this is yet another meteorite-forming stream that complements the list of 14 meteorite-forming streams that we found earlier [4]. These streams have an signi cance in terms of potential danger when they approach the Earth. The paper provides brief information about such a rare phenomenon, which is called the “chain fall” of meteorites by A. Brezina [5].

Più fonti

Tesi sul tema "Meteoroid stream":

Sekhar, A. "Evolution of Halley-type comets and meteoroid streams". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676720.

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The overall objective of the thesis is to understand the long term orbital dynamics of comets and meteoroid streams. The initial idea focused mainly on detailed analysis of Jovian resonances in Orionids and Leonids. Special emphasis was given to study their influences in causing meteoroutbursts and storms on Earth. The theoretical simulations matched with observational records to a very good degree. This work led to the curious question as to whether any resonance mechanism could be driven due to Saturn's gravity. Subsequent analysis showed that Saturn's influences can also become vital when the order of resonance (concerning Saturn) is smaller compared to that in the adjacentJovian resonances. Compact resonant structures (due to Saturn's effects) were identified in both Orionid and Leonid streams during present times. All these calculations were done solely using a Newtonian model. This raised more questions as to whether Einstein's general relativistic effects could have any substantial role during long term (of the order of thousand years) meteor shower forecasts. Analytical and numerical analysis showed that general relativistic effects could lead to significant errors (in long term forecasts) in some particular combinations (or different epochs) of Keplerian orbital elements in certain low perihelion distance (below 0.15 AU) and low semi-major axis (below 1.5 AU) meteoroid streams. Because some low perihelion distance meteoroid streams are associated with sungrazing comets, this led to the next question regarding the reason for the absence of meteor showers from this class of comets. A detailed study using Lagrange's planetary equations showed that most sungrazers cannot make the nodes of meteoroid particles Earth intersecting at low ejection velocities (of order 10 m/s). This can be used as a convincing argument to establish the absence of spectacular meteor showers on Earth from the frequently observed sungrazers so far.

Brown, Peter Gordon. "Evolution of two periodic meteoroid streams, the perseids and leonids". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0009/NQ40247.pdf.

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Harris, Nathan W. "Dust ejection from cometary nuclei and the formation of meteoroid streams". Thesis, University of Sheffield, 1994. http://etheses.whiterose.ac.uk/5968/.

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Costa, Tarcísio Oliveira da. "EVENTOS DE PRECIPITAÇÃO EXTREMA ASSOCIADOS ÀS INUNDAÇÕES NA ÁREA URBANA DE BRAGANÇA/PA". Universidade Federal de Santa Maria, 2014. http://repositorio.ufsm.br/handle/1/9431.

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The study of urban climate has a great importance in regard to the understanding of the human-nature relationship and the interaction between the local climate and the city. This expectation motivated this study on the Urban Climate in the city of Bragança, Pará State, a city that has undergone urban impacts from the rains that cause floods and flooding that hit several areas of the city, especially along the course from the Cereja stream, that is cutting the urban mesh. The Floods are one of the most serious problems which affects the cities when there is an occurrence of extreme precipitation events, generating impacts that affect the daily routine of the people. In this way, the choice for the study of meteoric impact of the channel, the third channel among the subsystems of the Urban Climate System (SCU), it is justified by the study of floods and flooding that happened in the city and the need to understanding the environmental conditions that originate. In this context, this study aimed to analyze the urban climate and extreme expectation events associated with the occurrence of floods and flooding in the urban area of Bragança. Therewith, we analyzed the occurrence of floods in Cereja stream and flooding in Bragança in 2004-2013 period; It was analyzed the variability of precipitation in urban areas from January to May, in 2014; we identified the atmospheric systems linked to extreme expectation events in the urban area of the city; however, the balance of participation of climate systems during the Amazon winter 2014 and it was made a map of climate risk in areas of extreme rainfall situations with sight to urban land use planning in the city. Therefore, the research was based on the SCU theory developed by Monteiro (1976). In the historic flood (2004-2013) were found 32 extreme events, that only 07 were classified as episodes of relevance for this study due to the impact of records in the urban area. The weather data analyzed was collected of the Weather Station Conventional of Tracuateua city (EMT) and Automatic Weather Station of Bragança (EMB) that belongs to INMET and a network of 07 rain gauges installed in the urban area of the city in 2014 which allowed a development of variability maps precipitation during the Amazon winter. Were also it was developed participation swing charts of atmospheric systems with satellite images from GOES 13 aid provided by INPE and Letters daily Synoptic of 00h and 12h provided by the Navy of Brazil. With the results, it was observed that the ZCIT has increased the participation in the occurrence of extreme events and urban impacts, and it was noted that there is a great variability of expectation in the study of the area, up to 161 mm between the northnortheast sector (Rainier) and the South-southwest sector (less rain). Finally we prepared a risk map as a tool for urban land in use planning, considering the local climate variable.
O estudo do clima urbano é de grande importância no que se refere à compreensão da relação homem-natureza e da interação entre o clima local e a cidade. Essa perspectiva motivou este estudo sobre o Clima Urbano de Bragança/PA, cidade que tem sofrido impactos urbanos oriundos das chuvas que provocam inundações e alagamentos que atingem diversas áreas da cidade, principalmente, ao longo do curso do Igarapé Cereja, que corta a malha urbana. As inundações são um dos graves problemas que afetam as cidades quando há ocorrência de eventos de precipitação extrema, gerando impactos que influenciam no cotidiano das populações. Nesse sentido, a escolha pelo estudo do canal do Impacto Meteórico, terceiro canal dentre os subsistemas do Sistema Clima Urbano (SCU), justifica-se pelo estudo das inundações e alagamentos que tem ocorrido em Bragança e pela necessidade de entendimento das condições climáticas que as originam. Nesse contexto, este trabalho teve como objetivo geral analisar o clima urbano e os eventos de precipitação extrema associados à ocorrência de inundações e alagamentos na área urbana de Bragança-PA. Com isso, analisou-se a ocorrência de inundações no Igarapé Cereja e alagamentos em Bragança no período de 2004-2013; analisou-se a variabilidade da precipitação na área urbana no período de janeiro à maio do ano de 2014; identificou-se os sistemas atmosféricos ligados aos eventos de precipitação extrema na área urbana de Bragança-PA; realizou-se o balanço de participação dos sistemas atmosféricos durante o inverno amazônico de 2014 e elaborou-se um mapa de áreas de risco climático em situações de extrema precipitação com vistas ao ordenamento territorial urbano do município. Para tanto, a pesquisa baseou-se na teoria do SCU elaborada por Monteiro (1976). No histórico de inundações (2004-2013) foram encontrados 32 eventos extremos, dos quais apenas 07 foram classificados como episódios de relevância para este estudo, devido aos registros de repercussão na área urbana. Os dados meteorológicos analisados foram coletados da Estação Meteorológica Convencional de Tracuateua (EMT) e Estação Meteorológica Automática de Bragança (EMB), pertencente ao INMET e por uma rede de 07 pluviômetros instalados na área urbana de Bragança/PA em 2014, que possibilitou elaboração de mapas da variabilidade da precipitação durante o inverno amazônico. Foram também elaborados gráficos de balanço de participação mensal dos sistemas atmosféricos, com auxílio de imagens do satélite GOES 13 disponibilizadas pelo INPE e Cartas Sinóticas diárias das 00h e 12h disponibilizadas pela Marinha do Brasil. Com os resultados, observou-se que a ZCIT tem maior participação na ocorrência de eventos extremos e impactos urbanos, além de observar-se que há uma grande variabilidade da precipitação na área de estudo, de até 161 mm entre o setor norte-nordeste (mais chuvoso) e o setor Sul-sudoeste (menos chuvoso). Por fim foi elaborado um mapa de riscos como instrumento para o ordenamento territorial urbano, considerando a variável climática local.

Libri sul tema "Meteoroid stream":

Ryabova, Galina O. Mathematical Modelling of Meteoroid Streams. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-51510-2.

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Mandelkehr, M. M. The 2300 BC Event: Vol 1 Archaeology and Geophysics & The Meteoroid Stream. Outskirts Press, 2006.

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Ryabova, Galina O. Mathematical Modelling of Meteoroid Streams. Springer, 2020.

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Capitoli di libri sul tema "Meteoroid stream":

Williams, I. P. "Meteoroid Stream Dynamics". In From Newton to Chaos, 199–208. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4899-1085-1_18.

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Cevolani, Giordano, Giuseppe Pupillo, Anton Hajduk e Vladimir Porubčan. "Observations of the Leonid Meteoroid Stream by a Multistation FS Radio System". In Leonid Storm Research, 265–76. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-017-2071-7_19.

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Steel, Duncan. "Meteoroid Streams". In Asteroids, Comets, Meteors 1993, 111–26. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1148-5_9.

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Williams, I. P. "The Dynamics of Meteoroid Streams". In Dynamics of Natural and Artificial Celestial Bodies, 103–13. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-017-1327-6_12.

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Williams, I. P. "Meteoroid Streams and Meteor Showers". In The Dynamics of Small Bodies in the Solar System, 179–85. Dordrecht: Springer Netherlands, 1999. http://dx.doi.org/10.1007/978-94-015-9221-5_17.

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Beech, Martin. "Characterizing the Annual Meteoroid Streams". In Protection of Space Materials from the Space Environment, 305–29. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0714-6_24.

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Williams, I. P., e Zidian Wu. "The Dynamics of Meteoroid Streams". In Predictability, Stability, and Chaos in N-Body Dynamical Systems, 225–38. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4684-5997-5_17.

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Williams, Iwan P. "Meteors, Meteor Showers and Meteoroid Streams". In Solar and Extra-Solar Planetary Systems, 243–55. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/3-540-44807-1_14.

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Babadzhanov, P. B., e Yu V. Obrubov. "Evolution Of Short-Period Meteoroid Streams". In Dynamics and Evolution of Minor Bodies with Galactic and Geological Implications, 111–27. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2743-1_8.

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Babadzhanov, P. B., e Yu V. Obrubov. "Dynamics and Spatial Shape of Short-Period Meteoroid Streams". In Highlights of Astronomy, 287–93. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0977-9_44.

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Atti di convegni sul tema "Meteoroid stream":

Stabroth, Sebastian, Michael Oswald, Carsten Wiedemann, Peter Vörsmann e Heiner Klinkrad. "Modelling the Meteoroid Stream Flux onto Targets in Earth Orbits". In AIAA/AAS Astrodynamics Specialist Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-6516.

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Granitskii, Lev V., e A. N. Borisevich. "Influence of the meteoric stream on weather conditions: preliminary consideration". In 7th International Symposium on Atmospheric and Ocean Optics, a cura di Gennadii G. Matvienko e Mikhail V. Panchenko. SPIE, 2000. http://dx.doi.org/10.1117/12.411998.

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Shchepalova, A. "Metrics in The Space of Keplerian Orbits and in the Family of Its Quotient Spaces". In ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.031.

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Abstract (sommario):

The distance functions on the set of Keplerian orbits play an important role in solving the problems of searching for theparent bodies of meteoroid streams. A special kind of function is the distances in the quotient spaces of orbits. Three metricsof this type were developed earlier. These metrics allow disregarding the longitude of the ascending node or the argumentof pericenter, or both. Recently, we introduced one more quotient space, where two orbits are considered to be identical ifthey diﬀer only in their longitudes of nodes and arguments of pericenters, but have the same sum of these elements (thelongitude of pericenter).

Rapporti di organizzazioni sul tema "Meteoroid stream":

Kidder, J. A., M. B. McClenaghan, M I Leybourne, M. W. McCurdy, P. Pelchat, D. Layton-Matthews, C. E. Beckett-Brown e A. Voinot. Geochemical data for stream and groundwaters around the Casino Cu-Au-Mo porphyry deposit, Yukon (NTS 115 J/10 and 115 J/15). Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/328862.

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This open file reports geochemical data for stream and groundwater samples collected around the Casino porphyry Cu-Au-Mo deposit, one of the largest and highest-grade deposits of its kind in Canada. The calc-alkaline porphyry is hosted in a Late Cretaceous quartz monzonite and associated breccias in the unglaciated region of west central Yukon. Water chemistry around the deposit was investigated because: (i) the deposit has not yet been disturbed by mining; (ii) the deposit was known to have metal-rich waters in local streams; and (iii) the deposit has atypically preserved ore zones. Stream water samples were collected at 22 sites and groundwater samples were collected from eight sites. Surface and groundwaters around the Casino deposit are anomalous with respect to Cd (up to 5.4 µg/L), Co (up to 64 µg/L), Cu (up to 1657 µg/L), Mo (up to 25 µg/L), As (up to 17 µg/L), Re (up to 0.7 µg/L), and Zn (up to 354 µg/L) concentrations. The stable isotopes of O and H of the groundwaters are essentially identical to the surface waters and plot close to the local and global meteoric water lines, indicating that the waters represent modern recharge, consistent with the generally low salinities of all the waters (total dissolved solids range from 98 to 1320 mg/L). Sulfur and Sr isotopes are consistent with proximal waters interacting with the Casino rocks and mineralization; a sulfide-rich bedrock sample from the deposit has delta-34S = -1.2 permille and proximal groundwaters are only slightly heavier (-0.3 to 3.1 permille). These geochemical and isotopic results indicate that surface water geochemistry is a suitable medium for mineral exploration for porphyry-style mineralization in the Yukon, and similar unglaciated regions in Canada. The atypical geochemical signature (Mo, Se, Re, As, Cu) of these types of deposits are typically reflected in the water chemistry and S isotopes provide a more local vectoring tool.

Ray, Laura, Madeleine Jordan, Steven Arcone, Lynn Kaluzienski, Benjamin Walker, Peter Ortquist Koons, James Lever e Gordon Hamilton. Velocity field in the McMurdo shear zone from annual ground penetrating radar imaging and crevasse matching. Engineer Research and Development Center (U.S.), dicembre 2021. http://dx.doi.org/10.21079/11681/42623.

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Abstract (sommario):

The McMurdo shear zone (MSZ) is strip of heavily crevassed ice oriented in the south-north direction and moving northward. Previous airborne surveys revealed a chaotic crevasse structure superimposed on a set of expected crevasse orientations at 45 degrees to the south-north flow (due to shear stress mechanisms). The dynamics that produced this chaotic structure are poorly understood. Our purpose is to present our field methodology and provide field data that will enable validation of models of the MSZ evolution, and here, we present a method for deriving a local velocity field from ground penetrating radar (GPR) data towards that end. Maps of near-surface crevasses were derived from two annual GPR surveys of a 28 km² region of the MSZ using Eulerian sampling. Our robot-towed and GPS navigated GPR enabled a dense survey grid, with transects of the shear zone at 50 m spacing. Each survey comprised multiple crossings of long (> 1 km) crevasses that appear in echelon on the western and eastern boundaries of the shear zone, as well as two or more crossings of shorter crevasses in the more chaotic zone between the western and eastern boundaries. From these maps, we derived a local velocity field based on the year-to-year movement of the same crevasses. Our velocity field varies significantly from fields previously established using remote sensing and provides more detail than one concurrently derived from a 29-station GPS network. Rather than a simple velocity gradient expected for crevasses oriented approximately 45 degrees to flow direction, we find constant velocity contours oriented diagonally across the shear zone with a wavy fine structure. Although our survey is based on near-surface crevasses, similar crevassing found in marine ice at 160 m depth leads us to conclude that this surface velocity field may hold through the body of meteoric and marine ice. Our success with robot-towed GPR with GPS navigation suggests we may greatly increase our survey areas.