季节背景对ENSO循环过程中SSTA增/减幅作用的数值试验研究     

管兆勇  周铁汉 《气象学报》2001,59(6):659-673

利用热带太平洋地区 2层区域海洋模式和再分析资料探讨了大气 /海洋的季节背景对ENSO时间尺度上海温异常的增幅或减幅作用。结果表明 :不论什么季节背景下 ,就海洋变化而言 ,El Nino/La Nina事件均可存在 ,说明 El Nino/La Nina事件的存在和维持并没有季节性选择 ;模式海洋的西太平洋赤道地区次表层海水温度异常变化位相明显超前于东太平洋SSTA且在空间上自西向东传播 ,同时有位相超前的量还包括模式第 1层厚度异常及热容量异常 ,这些对 ENSO的预测和机制研究具有重要意义。 SSTA的振幅在不同的季节背景下可受到不同的调节。以春季为背景 ,同样的异常风应力作用于海洋 ,可使 NINO3区 SSTA较正常季节背景下该区的 SSTA振幅明显增大 ;而在冬季背景下可使 SSTA受到一定程度的减幅 ,这说明 El Nino/L a Nina现象的发生和消亡有季节选择倾向。与春季背景下 NINO 3区SSTA的增幅倾向相反 ,模式第 1层厚度异常的振幅则受到削弱。而西太平洋赤道地区 ,模式海洋混合层的厚度异常则有所增强。这种与 SSTA增 /减幅反相关的现象需要进一步研究  相似文献   

STABILITY OF GRAVEL BED RIVERS BASED ON SIEVE ANALYSIS DATA   总被引：1，自引：0，他引：1  

Andreas DITTRICH Institute of Water Resources Management  Hydraulic  Rural Engineering  University of Karlsruhe  Germany. 《国际泥沙研究》2001,16(2)

the or are rm me un'.ox rm as n^nAndreas mlimcrbo was - ou at the -- of Karlsruh in the las l0 pe to meq esistingwt and wt our W on tbe bo Of th6 stabmp of bo edconSsting Of graVe and stones. Sbo in the ds mOuntain wt with tyPbo sbo Of I== 0.05% tO 0.8% as well as those with distinct ~ strUCtUres and slpe of I > 4% and I Sl0% were investipe. host ot the -- were conot in the bo--. bo som Of the results that bad bo for under tw COntwcoul be eded with ealsting field data. In the followin,…  相似文献   

A flume design for the study of slope length effects on runoff     

T. J. Stomph  N. De Ridder  N. C. Van De Giesen 《地球表面变化过程与地形》2001,26(6):647-655

Recent publications from field and simulation studies indicate that runoff per unit area decreases as the length of the slope being observed is increased. This scale effect has been observed and documented for slopes with a uniform infiltration capacity as well as for slopes along which infiltration capacity is variable. This paper presents the design and testing of a laboratory flume for the study of the processes that lead to this scale effect, particularly for the case of slopes covered with crops. The features of the flume include reliable experimental control of soil water content prior to rainfall, high intensity rainfall without erosion, uniform crop growth along the slope, and the option of varying the infiltration rate independently of rainfall and soil characteristics. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

The role of seepage in erodibility   总被引：1，自引：0，他引：1  

L. O. Owoputi  W. J. Stolte 《水文研究》2001,15(1):13-22

This paper describes a laboratory experimental study to examine the role of seepage in the soil‐water erosion process. The study utilized a laboratory flume, which was subjected to both seepage and rainfall in order to determine the exact character of the influence of seepage on erosion rates. The results from the experimental tests performed on sand and sandy clay till are reported. The experimental results show that seepage, by itself, has little effect on erosion rates. However, the erosion caused by rainfall is increased when seepage is present. The increased erosion was not caused by an increase in the total runoff from the seepage. It was found that seepage has an effect on the erodibility of the sand and sandy clay till. The results also show that the impact of seepage on the erodibility of the sand is greater than that of the sandy clay till. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Theme Issue on Confining Units     

Vicki Remenda 《Hydrogeology Journal》2001,9(1):3-4

  相似文献   

In situ and laboratory investigations of fluid flow through an argillaceous formation at different scales of space and time, Tournemire tunnel, southern France     

Jean-Yves Boisson  Lucien Bertrand  Jean-François Heitz  Yann Golvan 《Hydrogeology Journal》2001,9(1):108-123

In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron, France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10^–12 to 2×10^–11 m²/s) and hydraulic conductivities derived from different types of laboratory tests (10^–14 to 10^–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements) were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10^–13 to 10^–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling, based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture network do not permit reduction of uncertainties on these estimations at this stage. Electronic Publication  相似文献   

Characteristics of turnover of carbonyl sulfide in four different soils     

Susanne Lehmann  Ralf Conrad 《Journal of Atmospheric Chemistry》1996,23(2):193-207

Release and uptake of carbonyl sulfide (OCS) were measured at 25°C in samples of three forest soils (BL, BW, PBE) and one soil from a rape field (RA). The soil samples were flushed with a constant flow of either air (oxic conditions) or nitrogen (anoxic conditions) containing defined concentrations of OCS. A cryogenic trapping technique with liquid argon (-186 °C) was used to collect gas samples for analysis in a gas chromatograph equipped with a flame-photometric detector. The dependence of net OCS fluxes between soil and atmosphere could be described by a simple model of simultaneous OCS production and OCS uptake. By using this model, production rates (P), uptake rate constants (k) and compensation concentrations (m _c ) of OCS could be determined as function of the soil type and the incubation conditions. Under oxic conditions, OCS production (P) and uptake were observed in all soils tested. However, the compensation concentrations (<166 ng l^-1; 1 ng OCS l^-1=0.41 ppbv) that were calculated from the model were high relative to the ambient OCS concentration (ca. 0.5 ppbv). The production rates (0.16–1.9 ng h^-1 g^-1 dw) that were actually measured when flushing the soil samples with air containing zero OCS were smaller than those (17–114 ng h^-1 g^-1 dw) calculated from the model. This observation was explained by two different concepts: one assuming the existence of a threshold concentration (m _t ) below which OCS was no longer consumed in the soil; the other assuming the existence of two different OCS consumption processes, of which only the process active at elevated OCS concentrations was covered by the experiments. The latter concept allowed the estimation of OCS compensation concentrations that were partially low enough to allow the uptake of atmospheric OCS by soil. Both OCS production and uptake in PBE soil were dependent on soil temperature (optimum 20 °C) indicating a microbial process. However, both production and consumption of OCS were not consistently inhibited by sterilization of the soil, suggesting that they were not exclusively due to microbiological processes. Under anoxic conditions, OCS was also produced, but was not consumed except in one soil (RA). Production of OCS in the soils was stimulated after addition of thiocyanate, but not thiourea, thiosulfate, thioglycolate, tetrathionate, sulfate, elemental sulfur, cysteine and methionine.  相似文献   

Mineral magnetic properties of mixtures of environmental and synthetic materials: linear additivity and interaction effects   总被引：4，自引：0，他引：4  

Joan A. Lees 《Geophysical Journal International》1997,131(2):335-346

Mineral magnetic properties have been used recently to classify and to attempt to quantify the sources of sediments through environmental systems. Linear modelling techniques could be used with a wide range of concentration-dependent magnetic measurements to quantify the sources of sediments. To investigate wider application of linear modelling techniques using mineral magnetic properties, research has been conducted using laboratory mixtures of up to six source materials, including both natural environmental materials and synthetic compounds. While six sources may seem ambitious, this figure was used as an absolute upper limit rather than giving a real prospect of mathematically unmixing six sources. It has been found that even with the most magnetically differentiable materials, large errors are encountered when modelling the sources of the mixtures. This paper investigates the causes of 'non-additivity' of certain magnetic measurements and the failure of the linear modelling of the sources of the mixtures. Possible reasons for this failure include source homogeneity, calibration and linearity of equipment, magnetic viscosity of materials and/or the changing physical characteristics of the source materials once mixed together (interaction effects). In testing linear additivity, low-frequency susceptibility is the most reliable mineral magnetic measurement, while remanence measurements suffer from a systematic error in the expected results. Results have shown that in the best controlled conditions where the sources are identified and are artificially mixed together, the results of linear modelling are quite poor and at best four sources can be 'unmixed' with reasonable success. It is suggested that interaction within the mixtures, especially when containing highly ferrimagnetic burnt environmental materials, causes some of the non-additivity phenomena.  相似文献   

Neighbor competition modifies demographic responses of desert dune annuals to gradients in sand stability     

Ronen Kadmon 《Journal of Arid Environments》1997,36(4):557-564

A field experiment was conducted to test the hypothesis that competitive interactions affect demographic responses of desert dune annuals to gradients in sand stability. The experiment was based on a three-way factorial design with two types of neighbor treatments (complete neighbor removalvs. control), two types of habitats (stablevs. unstable sands) and two species which characterize sandy areas of the western Negev Desert (Neurada procumbensandBromus fasciculatus). Each of the eight treatment/habitat/species combinations was characterized by three demographic variables: seedling survival to reproduction, fruit number per reproductive plant and fruit number per seedling. All of these variables exhibited significant interactions between the effects of neighbor removal and habitat type, indicating that neighbor conditions were important in determining the observed patterns of demographic variation. Moreover, while plants ofNeurada procumbensgrowing without neighbors suffered more mortality on unstable sands, conspecific plants growing at natural density conditions suffered more mortality on stable sands. In the case ofBromus fasciculatus, individuals growing in the absence of competitive effects produced more fruits on stable sands, but conspecific plants growing at natural density conditions exhibited higher fruit production on unstable sands. These findings indicate that competitive effects not only modify, but may even reverse demographic responses of desert dune annuals to gradients in sand stability. Based on these results and evidence from two other studies it is suggested that seed dispersal from abiotically favorable into less favorable habitats may increase fitness of desert annuals by reducing the average effect of competition.  相似文献   

Statistical Distributions of Wavelengths     

Yu Dingyong Xu Delun Ph. D. Student  Engineering College  Ocean University of Qingdao  Qingdao Professor  Physical Oceanography Laboratory  Ocean University of Qingdao  Qingdao 《中国海洋工程》1997,(3)

The statistical distribution of wavelength is directly derived from a two-dimensional andspatially homogeneous Gaussian wave field.The present result differs from both the result of Rayleigh dis-tribution and Sun's result(1988b)which is transformed through the period distribution derived from atwo-dimensional and stationary Gaussian wave field.A laboratory experiment shows that the present re-sult is more consistent with the observations in the wave tank than the others.  相似文献