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A sequence of extreme ultraviolet (EUV) spectroheliograms of McMath region No. 10283 were obtained by the Harvard College Observatory experiment on OSO-6. The lines Ovi λ1032 Mg × λ625, Si xii λ499 and Fe xvi λ 335 were used to determine coronal temperatures and densities above the active region. A comparison of theoretical and observed line ratios yielded coronal temperatures of 2.2 to 2.3 × 106K above the active region and 2.0 to 2.1 × 106K in the surrounding area. The temperatures derived from ratios involving the O vi intensities are systematically higher than the others. This is attributed to an error in the theoretical O vi intensities. The intensities observed above the limb are compared with intensities predicted with a simple model based on cylindrical geometry. The overall agreement shows that the assumption of an iso-thermal corona in hydrostatic equilibrium above the active region is a reasonable working hypothesis and that the adopted geometrical model for the electron density distribution is adequate. 相似文献
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Nirupama Raghavan 《Solar physics》1983,89(1):35-42
Ca II spectroheliograms covering the period from 1912 to 1974 have been studied by using techniques of quantitative stereology. It is found that the fractional area α occupied by the emission network boundaries varies from 0.43 to 0.54, with the areal fraction being larger for years of sunspot minimum. The number of cells per unit area N A, decreases with increasing activity. The inner radius of the boundary wall has also been derived, as a function of epoch. While the width of the emission wall is nearly constant with activity, the average interior network cell size decreases with decreasing activity. 相似文献
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N. Nirupama 《Natural Hazards》2009,48(1):11-16
For the assessment of tsunami risk and vulnerability, one has to make use of past tsunami observations. The most comprehensive
tsunami databases for the world have been prepared by the National Geophysical Data Center of USA which are listed on their
website for all the four oceans as well as the following marginal seas: Caribbean Sea, Mediterranean Sea, Black Sea, Red Sea
and Gulf of Mexico. The dataset goes back as far as the first century AD and lists the events on a confidence rating scale
of 0–4; 0 being an erroneous entry and 4 being a definite tsunami. Based on these various datasets for different geographical
areas, a comprehensive global dataset was prepared in this study, which included only tsunami events with confidence rating
of 3 and 4, meaning either probable or definite. In this composite and abridged global tsunami database there is no distinction
either according to geography or tsunami strength as implied by its impact on the coast. A simple and straightforward statistical
analysis suggests an almost complete randomness and no patterns that can be used for future tsunami predictions with a few
minor exceptions. 相似文献
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The Indian Ocean tsunami of December 26, 2004, not only affected the Bay of Bengal coast of India but also part of the Arabian Sea coast of India. In particular, the tsunami caused loss of life and heavy damage on some parts of the Kerala coast in southwest India. The tsunami traveled west, south of Sri Lanka, and some of the tsunami energy was diffracted around Sri Lanka and the southern tip of India and moved northward into the Arabian Sea. However, tsunami, being a long gravity wave with a wave length of a few hundred kilometers, has to take a wide turn. In that process, it missed the very southern part of the Kerala coast and did not achieve large amplitudes there. However, further north, the tsunami achieved amplitudes of upto 5 m and caused loss of life and significant damage. Here we identify the physical oceanographic processes that were responsible for selective amplification of the tsunami in certain locations. 相似文献
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Compared to the Pacific Ocean, tsunamis are rare both in the Atlantic and Indian Oceans. However, the December 26, 2004, tsunami demonstrated that, no matter how rare they may be, when a major tsunami occurs, it could be very disastrous. The most basic information in tsunami warning center requires are charts showing tsunami travel times to various locations around the rim of the ocean. With this in mind, a tsunami travel time atlas for the Atlantic Ocean is in preparation. The Caribbean Sea is also included in this Atlas, as it is more or less a part of the Atlantic Basin. 相似文献
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M. Baba N. P. Kurian B. T. Murali Krishnan N. Nirupama T. S. Murty 《Marine Geodesy》2006,29(4):271-276
The Tsunami of December 26, 2004, in the Indian Ocean arrived on the coast of Kerala in southwest India some three hours after the tsunami was generated. The tsunami activity persisted throughout that day and, in some locations, even into the early morning of the next day. Based on interviews with eye witnesses, arrival times of tsunami waves are presented here followed by some preliminary analysis of the results. 相似文献
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The energetics of the most destructive tsunami in historical time, and that of the under ocean earthquake that triggered this tsunami of 26 December 2004 in the Indian Ocean have been briefly reviewed. This latest tsunami has several other unique characteristics besides being one of the worst natural disasters in human history. It is the first truly global tsunami after modern seismographic and sea level monitoring networks have been put in place. It was the first tsunami on record detected by a satellite, even though at present, global satellite coverage of the oceans for real time tsunami detection is not adequate. Finally, the energy associated with the tsunami and the earthquake that triggered it is so large that speculation has been made about the normal modes of oscillation of the earth, that were triggered by the earthquake as well as some suggestions, that some of the earth's rotational characteristics may have temporarily changed to a discernible degree. Here, we briefly review the energetics of the tsunami and the earthquake that triggered it. 相似文献
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