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E Vidal - One of the best experts on this subject based on the ideXlab platform.
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a meteorite crater on earth formed on september 15 2007 the carancas hypervelocity impact
Meteoritics & Planetary Science, 2009Co-Authors: G Tancredi, J Ishitsuka, P H Schultz, R S Harris, P Brown, D O Revelle, K Antier, Le A Pichon, D Rosales, E VidalAbstract:On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater-forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earths Atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of average parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.
James M Russell - One of the best experts on this subject based on the ideXlab platform.
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the influence of the several very large solar proton events in years 2000 2003 on the neutral middle Atmosphere
Advances in Space Research, 2005Co-Authors: Charles H Jackman, M T Deland, G Labow, Eric L Fleming, Debra K Weisenstein, Malcolm K W Ko, M Sinnhuber, John Anderson, James M RussellAbstract:Solar proton events (SPEs) are known to have caused changes in constituents in the Earths polar neutral middle Atmosphere. The past four years, 2000–2003, have been replete with SPEs. Huge fluxes of high energy protons entered the Earths Atmosphere in periods lasting 2–3 days in July and November 2000, September and November 2001 and October 2003. The highly energetic protons produce ionizations, excitations, dissociations and dissociative ionizations of the background constituents, which lead to the production of HOx (H, OH, HO2) and NOy (N, NO, NO2 ,N O 3 ,N 2O5, HNO3 ,H O 2NO2, ClONO2, BrONO2). The HOx increases lead to short-lived ozone decreases in the polar mesosphere and upper stratosphere due to the short lifetimes of the HOx constituents. Large mesospheric ozone depletions (>70%) due to the HOx enhancements were observed and modeled as a result of the very large July 2000 SPE. The NOy increases lead to long-lived stratospheric ozone changes because of the long lifetime of the NOy family in this region. Polar total ozone depletions >1% were simulated in both hemispheres for extended periods of time (several months) as a result of the NOy enhancements due to the very large SPEs. � 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.
Horváth Gábor - One of the best experts on this subject based on the ideXlab platform.
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Celestial Mechanics and Polarization Optics of the Kordylewski Dust Cloud in the Earth-Moon Lagrange Point L5 Part II. Imaging Polarimetric Observation: New Evidence for the Existence of Kordylewski Dust Cloud
'Oxford University Press (OUP)', 2019Co-Authors: Slíz-balogh Judit, Barta András, Horváth GáborAbstract:Telescopes mounted with polarizers can study the neutral points of the Earths Atmosphere, the solar corona, the surface of planets/moons of the Solar System, distant stars, galaxies and nebulae. These examples demonstrate well that polarimetry is a useful technique to gather astronomical information from spatially extended phenomena. There are two enigmatic celestial objects that can also effectively be studied with imaging polarimetry, namely the Kordylewski dust clouds (KDCs) positioned around the L4 and L5 triangular Lagrangian libration points of the Earth-Moon system. Although in 1961 the Polish astronomer, Kazimierz Kordylewski had observed two bright patches near the L5 point with photography, many astronomers assume that these dust clouds do not exist, because the gravitational perturbation of the Sun, solar wind and other planets may disrupt the stabilizing effect of the L4 and L5 Lagrange points of the Earth and Moon. Using ground-born imaging polarimetry, we present here new observational evidence for the existence of the KDC around the L5 point of the Earth-Moon system. Excluding artefacts induced by the telescope, cirrus clouds or condensation trails of airplanes, the only explanation remains the polarized scattering of sunlight on the particles collected around the L5 point. By our polarimetric detection of the KDC we think it is appropriate to reconsider the pioneering photometric observation of Kordylewski. Our polarimetric evidence is supported by the results of simulation of dust cloud formation in the L5 point of the Earth-Moon system presented in the first part of this paper
G Tancredi - One of the best experts on this subject based on the ideXlab platform.
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a meteorite crater on earth formed on september 15 2007 the carancas hypervelocity impact
Meteoritics & Planetary Science, 2009Co-Authors: G Tancredi, J Ishitsuka, P H Schultz, R S Harris, P Brown, D O Revelle, K Antier, Le A Pichon, D Rosales, E VidalAbstract:On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater-forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earths Atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of average parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.
P R Higbie - One of the best experts on this subject based on the ideXlab platform.
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a comparison of new calculations of 10be production in the Earths polar Atmosphere by cosmic rays with 10be concentration measurements in polar ice cores between 1939 2005 a troubling lack of concordance paper 1
arXiv: Geophysics, 2010Co-Authors: W R Webber, P R HigbieAbstract:Using new calculations of 10Be production in the Earths Atmosphere which are based on direct measurements of the 11-year solar modulation effects on galactic cosmic rays and spacecraft measurements of the cosmic ray energy spectrum, we have calculated the yearly average production of 10Be in the Earths Atmosphere by galactic and solar cosmic rays since 1939. During the last six 11-year cycles the average amplitude of these production changes is 36%. These predictions are compared with measurements of 10Be concentration in polar ice cores in both the Northern and Southern hemisphere over the same time period. We find a large scatter between the predicted and measured yearly average data sets and a low cross correlation ~0.30. Also the normalized regression line slope between 10Be production changes and 10Be concentration changes is found to be only 0.4-0.6; much less than the value of 1.0 expected for a simple proportionality between these quantities, as is typically used for historical projections of the relationship between 10Be concentration and solar activity. The distribution of yearly averages in the 10Be concentration level in the data from the Dye-3 ice core in Greenland for the time period 1939-1985, contains a "spike" of high concentration one year averages which is not seen in the production calculations. These and other features suggest that galactic cosmic ray intensity changes which affect the production of 10Be in the Earths Atmosphere are not the sole source of the 10Be concentration changes and confirm the importance of other effects, for example local and regional climatic effects, which could be of the same magnitude as the 10Be production changes.