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71.
72.
一次冬季锋面暴风雪天气过程的斜压边界层特征的观测分析 总被引:4,自引:0,他引:4
对STORM-FESTIOP17一次冬季锋面暴风雪天气过程的斜压边界层结构演变及特征进行了分析。发现:暖湿空气沿锋面抬升凝结成云,产生降水过程中释放的大量潜热显著增加锋两侧的水平温度差异,产生锋生。与锋生相伴,在锋前产生低空急流和高空急流。当锋生至最强时,锋两侧温差可达20K,锋前低空急流开始减弱,锋后低空急流增强,锋后冷平流开始主导锋两侧的环流系统。该冷平流削弱锋两侧的温度水平梯度,产生锋消作用。对这次锋面斜压对流边界层的湍流特征分析表明:在边界层之上切应力wv明显增大;湍能收支分析表明在边界层之上的风切变产生项很强,即大尺度天气系统有利于斜压对流边界层的发展,边界层内各量充分混合。这次冬季锋面暴风雪天气过程,冷锋前的低空南风急流从墨西哥湾携带来的充足水汽及锋区边界层大气的强斜压性是其产生的关键因子:冷锋过后,大尺度高空急流的作用更有利于对流边界层的充分发展。 相似文献
73.
The formation of cold air drainage flows in a shallow gully is studied during CASES-99 (Cooperative Atmosphere-Surface Exchange Study). Fast and slow response wind and temperature measurements were obtained on an instrumented 10-m tower located in the gully and from a network of thermistors and two-dimensional sonic anemometers, situated across the gully. Gully flow formed on clear nights even with significant synoptic flow. Large variations in surface temperature developed within an hour after sunset and in situ cooling was the dominant factor in wind sheltered locations. The depth of the drainage flow and the height of the down-gully wind speed maximum were found to be largest when the external wind speed above the gully flow is less than 2 m s-1. The shallow drainage current is restricted to a depth of a few metres, and is deepest when the stratification is stronger and the external flow is weaker. During the night the drainage flow breaks down, sometimes on several occasions, due to intermittent turbulence and downward fluxes of heat and momentum. The near surface temperature may increase by 6 ° C in less than 30 min due to the vertical convergence of downward heat flux. The mixing events are related to acceleration of the flow above the gully flow and decreased Richardson number. These warming events also lead to warming of the near surface soil and reduction of the upward soil heat flux. To examine the relative importance of different physical mechanisms that could contribute to the rapid warming, and to characterize the turbulence generated during the intermittent turbulent periods, the sensible heat budget is analyzed and the behaviour of different turbulent parameters is discussed. 相似文献
74.
The circulation and transport of freshwater generated by an idealized buoyant source is studied using a three-dimensional primitive equation model. Freshwater enters the continental shelf, turns anticyclonically and moves downstream in the direction of Kelvin wave propagation. In the region close to the source, the flow reaches an equilibrium in the bottom boundary layer so that freshwater does not spread offshore any further. This offshore equilibrium distance increases as we move downstream until the freshwater is able to feel the presence of the shelfbreak. A shelfbreak front forms and the shelfbreak prevents any further offshore spreading of freshwater in the bottom boundary layer.Two complimentary mechanisms are responsible for the slow cross-shelf migration of freshwater and subsequent trapping of shelfbreak fronts: bottom stress and topographic changes. The shelfbreak creates an active, dynamic process preventing leakage from the continental shelf region to the slope region. However, the dynamical process that traps the front to the shelfbreak is still unclear.The location of the shelfbreak front depends on four dimensionless parameters: scaled inlet volume transport, scaled breadth, scaled “diffusivity” and scaled shelf width. We develop empirical relations for predicting the location of the frontal bottom intersection, given these parameters. 相似文献
75.
球状地球体可控深度电法的效应系数可近似地全面表达可控深度电法和各种效应。通过点源二度体的电算模拟实验,证明了该方法在水平柱状体和地下存在电阻率垂直界面的条件下,也是有效的。 相似文献
76.
77.
EFG法在土体固结中的应用 总被引:4,自引:0,他引:4
EFGM作为一种新的数值计算方法,具有只需节点信息而无段单元的特性,故在解固结方程方面有很大的优势。在计算分析中,此法容易构造固结方程的EFGM刚度矩阵和处理不同边界条件。对单面排水等条件的计算结果表明,EFGM在解决固结变形问题上,精度较高,处理边界准确。 相似文献
78.
Ammonoid Succession of Setorym River (Verkhoyansk Area) and Problem of Permian—Triassic Boundary in Boreal Realm 总被引:4,自引:0,他引:4
YuriDZakharov 《中国地质大学学报(英文版)》2002,13(2):107-123
The presence of a single Otoceras species (O.boreale), morphologically very variable, at the base of the Nekuchan Formation in Verkhoyansk, we believe, is to be obvious. Some morphological evidence leaves no doubt that two described morphs of O. boreale are s strictly corresponding sexual dimorphic pair. It is very likely that Kummel‘s idea that Canadian. O. concavum Tozer is an invalid species is truthful, considering the range of variability seen in larger Siberian and Himalayan Otoceras fauna. Just above the upper Tatarian Imtachan Formation, the six stages of ammonoid succession can be recognized within the lower part of the Nekuchan Formation in the Setorym River Section:(a) Otoceras boreale;(b) Otoceras boreale-Tompophiceras pascoei; (c) Otoceras boreale-Tompophiceras pascoei-Aldanoceras;(d)Tompophiceras pascoei-Otoceras boreale-Aldanoceras;(e) Tompophiceras morpheous-T.pascoei-Aldanoceras;(f) Tompophiceras more pheous-T.pascoei-Wordieoceras domokhotovi-Ophiceras transitorium;(g)Tompophiceras morpheous-T.pascoei, corresponding to the Otoceras boreale and Tompophiceras morpheous zones. In spite of the domination of Otocerataceae or Xenodiscaceae in both oif these zones and the presence of some Permian type conodonts in the lower part of the Otoceras boreale Zone, they seem to be early Induan in age on the basis of the following arguments:(1) in contrast to the underlying regressive type sediments of the Upper Tatarian Imtachan Formation, both the Otoceras boreale and the Tompophiceras morpheous zones of the lowermost part of the Nekuchan Formation correspond to the single transgressive cycle;(2)typical early Induan ammonoids (Ophiceras and Wordieoceras) have been recognized in the Tompophiceras morpheous zone; (3) all described ammonoid succession stages (a-g) are characterized by very gradual changes and therefore correspond to the different parts of the single zone or to the different zones of the same stage, but not to the different systems (Permian and Triassic);(4)elsewhere in the Boreal realm (Arctic Canada), the conodont index species for the base of the Triassic, Hindeodus parvus, has been reported from the Otoceras boreale Zone. A new scheme of the phylogeny for the Otocerataceae and its Induan-Olenekian offspring (Araxceratidae-Otoceratidae-Vavilovitidae n.fam.-Proptychitidae-Arctoceratidae) and Xenodiscaceae is offered. 相似文献
79.
Christoph Gaedicke Hans-Ulrich Schlüter Hans Albert Roeser Alexander Prexl Bernd Schreckenberger Heinrich Meyer Christian Reichert Peter Clift Shahid Amjad 《Tectonophysics》2002,355(1-4)
The nature and origin of the sediments and crust of the Murray Ridge System and northern Indus Fan are discussed. The uppermost unit consists of Middle Miocene to recent channel–levee complexes typical of submarine fans. This unit is underlain by a second unit composed of hemipelagic to pelagic sediments deposited during the drift phase after the break-up of India–Seychelles–Africa. A predrift sequence of assumed Mesozoic age occurring only as observed above basement ridges is composed of highly consolidated rocks. Different types of the acoustic basement were detected, which reflection seismic pattern, magnetic anomalies and gravity field modeling indicate to be of continental character. The continental crust is extremely thinned in the northern Indus Fan, lacking a typical block-faulted structure. The Indian continent–ocean transition is marked on single MCS profiles by sequences of seaward-dipping reflectors (SDR). In the northwestern Arabian Sea, the Indian plate margin is characterized by several phases of volcanism and deformation revealed from interpretation of multichannel seismic profiles and magnetic anomalies. From this study, thinned continental crust spreads between the northern Murray Ridge System and India underneath the northern Indus Fan. 相似文献
80.