The three-dimensional morphology and direction of propagation of coronal mass ejections (CMEs) are essential information for identifying their source on the solar disk, for understanding the processes of their ejection and propagation in the corona, and for forecasting their possible impact with the Earth or any other objects in the solar system. The polarization of the Thomson scattering by an electron is known to provide information on its position with respect to the plane of the sky. This polarimetric technique is applied to reconstruct 15 CMEs on the basis of white-light polarized images obtained with the Large Angle Spectrometric Coronagraph (LASCO) C2, which have been extensively corrected for instrumental effects. It does provide valuable results in spite of the time delays between the three observations required to build the polarization maps. Most of these CMEs exhibit complex structures making a classification in terms of simple shapes such as arcade of loops or flux rope difficult or even questionable. Three of these CMEs benefited from multiple observations allowing us to follow their three-dimensional development as they propagated outward. All CMEs are tracked back to the solar surface and in several instances, active regions are identified as the probable sources. Finally, the projected speeds and masses derived from white-light unpolarized observations have been corrected for the projection angle to produce unbiased values.
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Lance B. Morrissey Philippe Janvier Simon J. Braddy John P. Bennett Susan B. Marriott Peter R. Tarrant 《Geology Today》2006,22(2):66-67
Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle. 相似文献
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Paul Gonez Hung Nguyên HuuPhuong Ta Hoa Gaël ClémentPhilippe Janvier 《Journal of Asian Earth Sciences》2012,43(1):51-63
Several outcrops of the Late Silurian and Devonian of the Ngoc Vung Series, northern Vietnam, yielded plant remains. The Late Silurian localities delivered the earliest known flora of the South China block. Although the fossils are fragmentary, they complement our knowledge about the global composition of the flora. The major components of the flora are plants with dichotomous habit and terminal bivalvate sporangia, which are close relatives to zosterophylls, and zosterophylls. Plants with possible euphyllophyte affinities and bryophytes are occasionally present. This floral composition is similar to that of the rich, younger South China block assemblages from the Posongchong and Xujiachong Formations of China, considered Pragian in age. The South China block flora is therefore likely to have been dominated by zosterophylls and pre-zosterophylls at least from the Late Silurian to the Pragian (i.e. a 20 million years long period). It also strengthens the hypothesis that more derived plants were present on eastern Gondwana earlier that elsewhere, in the first steps of tracheophyte evolution. The Devonian localities of the Ngoc Vung Series delivered a thick fibrous stem fragment and a basal euphyllophyte. These latter plant remains provide some stratigraphic data. The large stem fragment is consistent with an Eifelian age for the Duong Dong Formation (part of the Ngoc Vung Series), as suggested by the brachiopod fauna. The accompanying basal euphyllophyte displays a combination of characters (axes 3-4 mm wide and lateral branchings) that is also consistent with an Eifelian age, but possibly more characteristic of the Emsian flora. It is therefore suggested that the stratigraphic range of the Duong Dong Formation might be extended down to the Emsian. 相似文献
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A. Blieck P. -Y. Gagnier F. P. Bigey G. D. Edgecombe P. Janvier S. Loboziak P. R. Racheb
uf T. Sempere P. Steemans 《Journal of South American Earth Sciences》1996,9(5-6)
An examination of Palaeozoic sections west of Cochabamba, and west of Lake Poopó, in western Bolivia, was conducted during a field expedition in 1991. The Río Iglesiani valley, west of Cochabamba, surprisingly yielded a Middle Devonian age to all the visited sites, originally supposed to be Ordovician. This result is based on spores, shelly faunas (brachiopods and bivalves), and trilobites. The Copacabana de Andamarca section, west of Lake Poopó, is also dated as Middle Devonian on account of its rather rich fauna (bryozoans, corals, brachiopods, conulariids, hyolithids, tentaculitids, ostracodes, trilobites, crinoids, vertebrates). Both localities correlate to the Icla and/or Huamampampa Formation of the Tarabuco area and Subandean belt, and to the Belén and/or Sica Sica Formation of the northern Altiplano. 相似文献
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Gouet Daniel Herv&#; Kana Janvier Domra Oya Valentin Ewembe Fontama Yuka 《Hydrogeology Journal》2022,30(4):1055-1069
Hydrogeology Journal - Lom River basin, associated with outflow from the Lom River system, is located in the East Region of Cameroon. The geology of the basin comprises Precambrian crystalline and... 相似文献
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Flux ropes are twisted magnetic structures that can be detected by in-situ measurements in the solar wind. However, different properties of detected flux ropes suggest different types of flux-rope populations. As such, are there different populations of flux ropes? The answer is positive and is the result of the analysis of four lists of flux ropes, including magnetic clouds (MCs), observed at 1 AU. The in-situ data for the four lists were fitted with the same cylindrical force-free field model, which provides an estimate of the local flux-rope parameters such as its radius and orientation. Since the flux-rope distributions have a broad dynamic range, we went beyond a simple histogram analysis by developing a partition technique that uniformly distributes the statistical fluctuations across the radius range. By doing so, we found that small flux ropes with radius R<0.1 AU have a steep power-law distribution in contrast to the larger flux ropes (identified as MCs), which have a Gaussian-like distribution. Next, from four CME catalogs, we estimated the expected flux-rope frequency per year at 1 AU. We found that the predicted numbers are similar to the frequencies of MCs observed in-situ. However, we also found that small flux ropes are at least ten times too abundant to correspond to CMEs, even to narrow ones. Investigating the different possible scenarios for the origin of these small flux ropes, we conclude that these twisted structures can be formed by blowout jets in the low corona or in coronal streamers. 相似文献
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