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21.
Identifying individual rain events from pluviograph records: a review with analysis of data from an Australian dryland site 总被引：3，自引：0，他引：3
David Dunkerley 《水文研究》2008,22(26):5024-5036
Rainfall is routinely reported as falling in ‘events’ or ‘storms’ whose beginning and end are defined by rainless intervals of a nominated duration (minimum inter‐event time, MIT). Rain events commonly exhibit fluctuations in rain rate as well as periods when rain ceases altogether. Event characteristics such as depth, mean rain rate, and the surface runoff volume generated, are defined in relation to the length of the rain event. These derived properties are dependent upon the value of MIT adopted to define the event, and the literature reveals a wide range of MIT criteria. Surprisingly little attention has been paid to this dependency, which limits the inter‐comparison of results in published work. The diversity in criteria also diminishes the usefulness of historical data on event durations, rain rates, etc., in attempts to document changes in the rainfall climate. This paper reviews the range of approaches used in the recognition of rain events, and a 5 year pluviograph record from an arid location is analysed. Changing MIT from 15 min to 24 h (lying within the range of published criteria) alters the number of rain events from 550 to 118. The mean rain rate declines from 2·04 mm h?1 to 0·94 mm h?1, and the geometric mean event duration rises from 0·66 h to 3·98 h. This wide variation in the properties of rain events indicates that more attention needs to be paid to the selection and reporting of event criteria in studies that adopt event‐based data analysis. The selection of a MIT criterion is shown to involve a compromise between the independence of widely‐spaced events and their increasingly variable intra‐event characteristics. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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D. L. Dunkerley 《水文研究》2008,22(12):1985-1995
Interception losses from the canopies of dryland plant taxa remain poorly understood, especially the relative contributions of intra‐storm and post‐storm evaporative losses. Employing a new measuring apparatus, this study uses low‐intensity simulated rain, matched to the properties of local rain, to explore interception processes in bluebush shrubs at an Australian dryland site. Five shrub specimens were exposed to simulated rain for 60–90 min. Experiments were repeated at three rainfall intensities (10, 15, and 20 mm h?1). Canopy evaporation was found from the difference between the flux of water delivered to the shrub and the flux of throughfall, once equilibrium had been established. The results show that evaporation from the wet foliage during rain proceeds at an average rate of 3·6 mm h?1. This figure is for relatively cool spring‐season conditions; evaporation rates in hot summer conditions would be larger. Intra‐storm evaporation is shown to exceed post‐rain evaporation from interception storage on the shrubs, and this differentiates dryland shrub interception processes from those of the better‐studied wet forest environment. Implications of the high dryland shrub canopy evaporation rates for aspects of dryland ecology are highlighted. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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The Winding Stair Gap in the Central Blue Ridge province exposes granulite facies schists, gneisses, granofelses and migmatites characterized by the mineral assemblages: garnet–biotite–sillimanite–plagioclase–quartz, garnet–hornblende–biotite–plagioclase–quartz ± orthopyroxene ± clinopyroxene and orthopyroxene–biotite–quartz. Multiple textural populations of biotite, kyanite and sillimanite in pelitic schists support a polymetamorphic history characterized by an early clockwise P–T path in which dehydration melting of muscovite took place in the stability field of kyanite. Continued heating led to dehydration melting of biotite until peak conditions of 850 ± 30 °C, 9 ± 1 kbar were reached. After equilibrating at peak temperatures, the rocks underwent a stage of near isobaric cooling during which hydrous melt ± K‐feldspar were replaced by muscovite, and garnet by sillimanite + biotite + plagioclase. Most monazite crystals from a pelitic schist display patchy zoning for Th, Y and U, with some matrix crystals having as many as five compositional zones. A few monazite inclusions in garnet, as well as Y‐rich cores of some monazite matrix crystals, yield the oldest dates of c. 500 Ma, whereas a few homogeneous matrix monazites that grew in the main foliation plane yield dates of 370–330 Ma. Culling and analysis of individual spot dates for eight monazite grains yields three age populations of 509 ± 14 Ma, 438 ± 5 Ma and 360 ± 5 Ma. These data suggest that peak‐temperature metamorphism and partial melting in the central Blue Ridge occurred during the Salinic or Taconic orogeny. Following near isobaric cooling, a second weaker thermal pulse possibly related to intrusion of nearby igneous bodies resulted in growth of monazite c. 360 Ma, coinciding with the Neoacadian orogeny. 相似文献
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大孔径闪烁仪观测数据的处理方法研究 总被引：2，自引：0，他引：2
大孔径闪烁仪可以获取公里级尺度的显热/潜热通量,其观测数据在农林业、水文、气象等领域的研究中具有越来越重要的作用.以海河流域2008年密云站和馆陶站大孔径闪烁仪的观测数据为例,讨论了数据筛选与处理方法,以及大气不稳定状态下不同处理方法对显热通量造成的影响.结果表明:空气折射指数结构参数应结合电压信号的方差进行计算、采用逐日的日平均波文比系数进行湿度订正、结合空间权重函数计算有效高度、选取Andreas(1988)稳定度函数计算显热通量等是可信的.通过对不同插补方法的比较可知,采用非线性回归方法和以零值替代的方法对不稳定状态和稳定状态下30 min缺失的显热通量进行插补,采用动态线性回归方法对日显热通量的缺失进行插补是可行的.为了解决由于冬天净辐射和显热通量较小,造成能量平衡方程余项法计算的蒸散量产生较大误差的问题,可采用根据大孔径闪烁仪与涡动相关仪观测的日蒸散量建立的关系式进行估算.基于上述方法的研究,形成了一套较为完整的大孔径闪烁仪观测数据的处理流程,保证了在不同下垫面、不同的天气状况条件下都能获取质量可靠、数据连续的大孔径闪烁仪观测的显热/潜热通量. 相似文献
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Evidence of Magma Mixing in the 'Daly Gap' of Alkaline Suites: a Case Study from the Enclaves of Pantelleria (Italy) 总被引：4，自引：0，他引：4
The island of Pantelleria consists of trachytes, pantelleritesand minor mildly alkaline basalts. Rocks of intermediate composition(falling in the so-called ‘Daly Gap’) such as mugearites,benmoreites and mafic trachytes occur only in the form of enclavesin trachytes and pantellerites inside the main caldera of theisland (Caldera ‘Cinque Denti’), which collapsedduring the ‘Green Tuff’ ignimbrite eruption at 50ka. The enclaves include volcanic, subvolcanic and intrusiverock types. The enclaves in host trachyte contain traces ofglass; devitrified glass occurs within enclaves in host pantellerites.Minerals in the enclaves show regular compositional variationswith whole-rock silica content. Glass present in the medium-grainedsamples is interpreted to be the result of incipient melting.The major and trace element compositions of the enclaves showregular and linear variations between an evolved mafic magma(hawaiite) and a felsic end-member similar to the ‘GreenTuff’ trachyte. Fractional crystallization modelling ofcompatible and incompatible trace elements (V, Ni, Zr, La, Sm,Lu, Nb, Y, Th) does not reproduce the observed trends. Rocksof intermediate composition within the ‘Daly Gap’can be explained only by magma mixing between an already differentiatedmafic magma (hawaiite) and an anorthoclase-rich trachytic meltin the lower and higher parts, respectively, of a stratifiedmagmatic chamber. Medium-grained enclaves are interpreted asthe result of fragmentation of solidified mixing layers in theroof of the magma chamber during the eruption of the ‘GreenTuff’, when the collapse of the caldera took place. Diffusioncalculations suggest a residence time of <5 days for theenclaves in their host magmas. KEY WORDS: Daly Gap; enclaves; magma mixing; Pantelleria 相似文献
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气候变化背景下森林动态模拟研究综述 总被引：2，自引：0，他引：2
在全球气候变化背景下,森林的地理分布与生态过程研究受到越来越多的关注.森林对气候变化的响应是一个复杂的过程,在已有模拟方法中,林窗模型和全球植被动态模型由于考虑了气候作用下植被的演替与更新等机理,能较为合理地模拟气候变化背景下森林的瞬态响应,是目前气候变化研究的热点之一.全球植被动态模型以植物功能类型(PFTs)表示区域森林植被组成,通过模拟PFTs比例的变化来反映森林地理分布格局的动态变化.通过回顾上述两类模型的发展历程,梳理了模型在模拟研究森林地理分布及生态过程中,对过去和未来气候变化的潜在响应方面的应用,并针对模型中存在的不足,提出今后应在动态模型多尺度研究、加强模型对非气候因子的描述、模型间比较、多源遥感数据与模型同化等方面开展重点研究. 相似文献
28.
While the global network of marine protected areas (MPAs) has recently been evaluated in the light of bio-geographic targets, there has been no attempt to evaluate the relative conservation efforts made by the different nations with regards to their level of socio-economic development. Using information mostly gathered from the world database on protected areas (WDPA), this paper gives a comparative assessment of MPA progress in countries from different economic categories, ranging from advanced economies to least developed countries (LDCs). Potentially explanatory socio-economic and environmental factors, such as fishing activity and existence of vulnerable marine ecosystems, for variability between nations in the level of MPA implementation are also explored. Existing MPA databases demonstrate a clear gap between developed and developing nations in MPA establishment, with advanced economies accounting for two thirds of the global MPA network. Patterns of MPA use, however, remain extremely heterogeneous between countries within each development group. International agreements on marine conservation, above and beyond the influence of country socio-economic and environmental profiles, are identified as a stimulating factor to MPA implementation. The level dependence on marine resource extraction appears to impede MPA implementation, though the relationship is not statistically significant due to large heterogeneity among countries. Leading developed nations increasingly use MPAs to designate integrated and adaptive management areas, and implementation of large “no-take” reserves in relatively-pristine overseas areas continues to accelerate. These analyses highlight certain limitations regarding our ability to assess the true conservation effectiveness of the existing global MPA network and the need for improved indicators of MPA restrictions and management efforts. 相似文献
29.
Subinertial fluctuation of a strong northward deep current, which is referred to the Dokdo Abyssal Current (DAC) by Chang et al. (2009), is investigated from current records for about 16.5 and 8.0 months in the Ulleung Interplain Gap of the East/Japan Sea. The current below 300 m is bottom-intensified and has nearly depth-independent flow. Near bottom, the spectral peaks of the current were found near 10, 20, and 60 d. The DAC variability near 10 d and 20 d is reasonably consistent with the linear theory of topographic Rossby waves (TRWs) in the following aspects: (1) The motion is columnar and bottom-intensified; (2) the theoretical cutoff frequency is similar to the observation; (3) The observation-based angles of the wavenumber vector are in good agreement with the theoretical ones. The wavelengths of the TRWs with periods of near 10 d and 20 d near Dokdo are significantly shorter than those with similar timescales in the open oceans (100-250 km). It is primarily due to the weak stratification below 300 m in the East Sea. The deep current fluctuations with periods of near 10 d and 20 d were accompanied by warm events in the upper layer resulting from eddying processes and/or meandering of the Tsushima Warm Current. 相似文献
30.
A criterion, allowing one to assess conditions likely togenerate gap flows and/or hydraulicjumps in stratified flows over a mountain ridge or a mountain pass,is derived. It is based on the one-dimensional reduced-gravity shallow-watertheory generalized to a three-dimensional orography with moderate streamwisevariations by introducing a variable effective flow cross-section. In this way,the hydraulic jump and gap flow are accommodated within the same model. Theresulting steady hyperbolic problem is shown to require the boundaryconditions to be expressed in terms of Riemann invariants. The latter yield the flow betweentwo given sites in a unique way. In particular, it is possible to relateunambiguously the existence of a hydraulic jump/gap flow and its energydiscontinuity to the boundary conditions. A simple method of flow interpolationand energy discontinuity calculation between two sites is presented. 相似文献