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81.
K. M. Gierens U. Schumann H. G. J. Smit M. Helten G. Zangl 《Annales Geophysicae》1997,15(8):1057-1066
Humidity and temperature fluctuations at pressure levels between 166 and 290 hPa on the grid scale of general circulation models for a region coveredn by the routes of airliners, mainly over the Atlantic, have been determined by evaluation of the data obtained with almost 2000 flights within the MOZAIC programme. It is found that the distributions of the fluctuations cannot be modelled by Gaussian distributions, because large fluctuations appear with a relatively high frequency. Lorentz distributions were used for the analytical representation of the fluctuation distributions. From these a joint probability distribution has been derived for simultaneous temperature and humidity fluctuations. This function together with the criteria for the formation and persistence of contrails are used to derive the maximum possible fractional coverage of persistent contrails in a grid cell of a GCM. This can be employed in a statistical formulation of contrail appearance in a climate model. 相似文献
82.
83.
Subsistence in coastal fisheries policy: What's in a word? 总被引：1，自引：2，他引：1
Consideration of subsistence fishing activities seems particularly relevant to coastal fisheries policy, yet formal recognition of subsistence fishing is often absent from associated policy frameworks. A critical problem is the very meaning of the term “subsistence.” A review of the literature on subsistence, dominated until recently by North American research, reveals a schism between interpretations emphasizing material aspects of subsistence and interpretations highlighting cultural aspects. The North American literature on the subject is heavily influenced by a focus on Arctic indigenous populations emphasizing cultural survival. Ultimately, subsistence can be a matter of survival in the belly, the soul, or both. International case studies suggest that different interpretations of subsistence are appropriate in different circumstances, and that appropriate policy can be fashioned only after the local context of subsistence is understood. 相似文献
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85.
R. Sausen K. Gierens M. Ponater U. Schumann 《Theoretical and Applied Climatology》1998,61(3-4):127-141
Summary The global distribution of contrail formation potential and contrail cloud coverage are estimated using meteorological analyses
of temperature and humidity (ECMWF re-analyses) and an aircraft fuel inventory. A large potential for contrail formation is
found in the upper troposphere, in particular in the tropics, but also at mid-latitudes. The global potential contrail coverage
is calculated to be 16%.
The actual contrail coverage is proportional to the product of the potential coverage and the fuel consumption of 1991/92
air traffic. The actual global contrail coverage is 0.09%, however, the pattern of main air routes show up in the geographical
distribution of contrail coverage with maximum values of more than 5%. Regionally, contrail coverage shows a distinct annual
cycle, with larger values in winter than in summer, in the mid-latitudes. The result is only weakly sensitive to the propulsion
efficiency of aircraft, but strongly sensitive to aircraft flight altitude.
Received October 1, 1997 Revised July 10, 1998 相似文献
86.
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88.
By the aid of a goniometer with the optic of a microscope it is possible to measure well reproducible the principal angle of incidence of a polished ore section. It may be used as a standard material constant for identifications. By the use of objective methods, with the aid of photomultiplier tubes and analysis by computation an accuracy of some few minutes of arc is within reach. Whereby certainly the quality of the sections and the polishing have to satisfy high requirements. The measurements are done without using a standard of comparison. They may be used as complement to the common measurements by vertical illumination. Details of the object are measurable down to a minimum diameter of about 15 m. 相似文献
89.
ABSTRACTFlood quantile estimation based on partial duration series (peak over threshold, POT) represents a noteworthy alternative to the classical annual maximum approach since it enlarges the available information spectrum. Here the POT approach is discussed with reference to its benefits in increasing the robustness of flood quantile estimations. The classical POT approach is based on a Poisson distribution for the annual number of exceedences, although this can be questionable in some cases. Therefore, the Poisson distribution is compared with two other distributions (binomial and Gumbel-Schelling). The results show that only rarely is there a difference from the Poisson distribution. In the second part we investigate the robustness of flood quantiles derived from different approaches in the sense of their temporal stability against the occurrence of extreme events. Besides the classical approach using annual maxima series (AMS) with the generalized extreme value distribution and different parameter estimation methods, two different applications of POT are tested. Both are based on monthly maxima above a threshold, but one also uses trimmed L-moments (TL-moments). It is shown how quantile estimations based on this “robust” POT approach (rPOT) become more robust than AMS-based methods, even in the case of occasional extraordinary extreme events.
Editor M.C. Acreman Associate editor A. Viglione 相似文献
90.
Insights from trace element geochemistry as to the roles of subduction zone geometry and subduction input on the chemistry of arc magmas 总被引：2，自引：0，他引：2
Heidi Wehrmann Kaj Hoernle Dieter Garbe-Schönberg Guillaume Jacques Julia Mahlke Kai Schumann 《International Journal of Earth Sciences》2014,103(7):1929-1944
Subduction zones of continental, transitional, and oceanic settings, relative to the nature of the overriding plate, are compared in terms of trace element compositions of mafic to intermediate arc rocks, in order to evaluate the relationship between subduction parameters and the presence of subduction fluids. The continental Chilean Southern Volcanic Zone (SVZ) and the transitional to oceanic Central American Volcanic Arc (CAVA) show increasing degrees of melting with increasing involvement of slab fluids, as is typical for hydrous flux melting beneath arc volcanoes. At the SVZ, the central segment with the thinnest continental crust/lithosphere erupted the highest-degree melts from the most depleted sources, similar to the oceanic-like Nicaraguan segment of the CAVA. The northern part of the SVZ, located on the thickest continental crust/lithosphere, exhibits features more similar to Costa Rica situated on the Caribbean Large Igneous Province, with lower degrees of melting from more enriched source materials. The composition of the slab fluids is characteristic for each arc system, with a particularly pronounced enrichment in Pb at the SVZ and in Ba at the CAVA. A direct compositional relationship between the arc rocks and the corresponding marine sediments that are subducted at the trenches clearly shows that the compositional signature of the lavas erupted in the different arcs carries an inherited signal from the subducted sediments. 相似文献