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排序方式: 共有238条查询结果,搜索用时 31 毫秒
181.
182.
Gill M.MARTIN Amulya CHEVUTURI Ruth E.COMER Nick J.DUNSTONE Adam A.SCAIFE Daquan ZHANG 《大气科学进展》2019,36(3):253-260
Predicting monsoon onset is crucial for agriculture and socioeconomic planning in countries where millions rely on the timely arrival of monsoon rains for their livelihoods. In this study we demonstrate useful skill in predicting year-to-year variations in South China Sea summer monsoon onset at up to a three-month lead time using the GloSea5 seasonal forecasting system. The main source of predictability comes from skillful prediction of Pacific sea surface temperatures associated with El NiÑo and La NiÑa. The South China Sea summer monsoon onset is a known indicator of the broadscale seasonal transition that represents the first stage of the onset of the Asian summer monsoon as a whole. Subsequent development of rainfall across East Asia is influenced by subseasonal variability and synoptic events that reduce predictability, but interannual variability in the broadscale monsoon onset for East Asian summer monsoon still provides potentially useful information for users about possible delays or early occurrence of the onset of rainfall over East Asia. 相似文献
183.
The origin of two ridges on the eastern slopes of Mt Allen, southern Stewart Island, has remained equivocal, with differences of opinion over the exact process-mechanisms of formation. A variety of approaches was used to test a number of possible hypotheses about the origin of the ridges. These include topographic and spatial positioning, geomorphology, sedimentology and palaeoclimatological extrapolations to reconstruct two small former cirque glaciers with equilibrium line altitudes (ELAs) of c. 600 m. It would appear the two ridges reflect a glacial origin, the glaciers interpreted as forming during the Last Glacial Maximum (LGM) in New Zealand. Whilst glaciation during this time (18–19 ka) was extensive in the Southern Alps, the restricted nature of glaciation on Mt Allen suggests the low altitude restricted glaciation to niche sites on the lee side of upland areas. 相似文献
184.
JOHN R. APPLEBY MARTIN S. BROOK SIMON S. VALE AMANDA M. MACDONALD‐CREEVEY 《Geografiska Annaler: Series A, Physical Geography》2010,92(4):451-467
This paper describes the structural glaciology of the lower Fox Glacier, a 12.7 km‐long valley glacier draining the western side of the Southern Alps, New Zealand. Field data are combined with analysis of aerial photographs to present a structural interpretation of a 5 km‐long segment covering the lower trunk of the glacier, from the upper icefall down‐glacier to the terminus. The glacier typifies the structural patterns observed in many other alpine glaciers, including: primary stratification visible within crevasse walls in the lower icefall; foliation visible in crevasses below the lower icefall; a complex set of intersecting crevasse traces; splaying and chevron crevasses at the glacier margins; transverse crevasses forming due to longitudinal extension; longitudinal crevasses due to lateral extension near the snout; and, arcuate up‐glacier dipping structures between the foot of the lower icefall and the terminus. The latter are interpreted as crevasse traces that have been reactivated as thrust faults, accommodating longitudinal compression at the glacier snout. Weak band‐ogives are visible below the upper icefall, and these could be formed by multiple shearing zones uplifting basal ice to the glacier surface to produce the darker bands, rather than by discrete fault planes. Many structures such as crevasses traces do not show a clear relationship with measured surface strain‐rates, in which case they may be ‘close to crevassing’, or are undergoing passive transport down‐glacier. 相似文献
185.
The validity of the response spectrum concept for determining loads in structures excited by differential earthquake ground motion is examined. It is shown that the common definition of response spectrum for synchronous ground motion can be reconciled to remain valid in cases when the columns of extended structures experience different motions. Then, a relative displacement response spectrum for design of first-storey columns, SDC(T, δ, ζ, τ), is defined. In addition to natural period, T, and fraction of critical damping, ζ, this spectrum depends also on the ‘travel time’, τ (of the waves in the soil over distances about one half width, or length of the structure), and on a factor, δ, specifying the relative displacement of the first floor. It is shown how this spectrum can be determined using existing empirical scaling equations for relative displacement spectra SD(T, ζ) and for peak velocity and peak acceleration of strong ground motion. These new spectra are illustrated for a horizontal component of a record in the near field of the 1994 Northridge earthquake. The results show that differential motions are more important for short period (stiff) than for longer period (flexible) structures, and for structures founded on softer ground (small shear wave velocity). © 1997 by John Wiley & Sons, Ltd. 相似文献
186.
桑沟湾和胶州湾沉积物耗氧率研究 总被引:2,自引:0,他引:2
为评价浅海海域底层在碳元素生物地化循环中的作用,采用现场取样培养法测定了黄海桑沟湾和胶州湾的沉积物耗氧率。桑沟湾5月和8月的沉积物耗氧率分别为15和24 mmol.m-2.d-1;胶州湾8月的沉积物耗氧率为18 mmol.m-2.d-1。回归分析表明,2个湾的沉积物耗氧率分别与沉积物表层的有机碳和总氮含量正相关。取呼吸商为0.8,得到桑沟湾底层对有机碳的矿化率占水层初级生产力的102%(5月)和67%(8月),胶州湾底层对有机碳的矿化率占水层初级生产力的28%(8月)。取桑沟湾颗粒有机碳的生物沉积速率为236 mg.m-2.d-1,得到底层对有机碳的埋置效率为40%(5月)和3%(8月),埋置的有机碳占水层初级生产力的69%(5月)和2%(8月);胶州湾颗粒有机碳的自然沉积速率为251 mg.m-2.d-1,底层对有机碳的埋置效率为32%(8月),埋置的有机碳占水层初级生产力的13%(8月)。 相似文献
187.
ABSTRACT. The area-studies model of global scholarship, based on dividing the world into a set number of large, quasi-continental regions, is under assault from a variety of intellectual and institutional forces. New, less rigid models of global scholarship are increasingly being called for by both scholars and funding agencies. One useful alternative, currently being explored at Duke University, reframes area studies around ocean and sea basins. Putting maritime interactions at the center of vision brings to light a set of historical regions that have largely remained invisible on the conventional map of the world. 相似文献
188.
ELIZABETH MANCKE 《Geographical review》1999,89(2):225-236
ABSTRACT. The definition of oceans as international politicized space is an integral but little analyzed aspect of early modern European expansion, which took place between about 1450 and 1800. In this essay I explore the implications of thinking about the development of European imperialism and global dominance in oceanic terms. I argue that oceanic, rather than terrestrial, dominance characterized early modern European empires, particularly in relation to Africa and Asia, where indigenous political and economic control prevailed. The long apprenticeship in mastering oceanic space contributed to the ability of Europeans to build land-based empires in Asia and Africa in the nineteenth century. As well, the international relationships worked out by Europeans in the nonstate but militarized arena of the high seas contributed to an emergent global order. 相似文献
189.
190.