Influence of Tropical Cyclones of the South China Sea on the Variability of the Vietnamese Coastal Current Structure     

Vlasova  G. A.  Nguyen  Xuan Ba  Le  Mau Dinh  Marchenko  S. S. 《Oceanology》2022,62(1):13-21

The state of the natural environment of the marginal seas of the Northwest Pacific is largely controlled by the interaction of the atmospheric and hydrophysical processes. Tropical cyclones (typhoons), originating in the tropical zone of the Northwest Pacific and over the South China Sea basin, occupy a special place among atmospheric processes. The main destructive impact of typhoons falls on Southeast Asia. However, a significant number of are moving to the Russian Far East. The region of the South China Sea plays a significant role in the formation of tropical cyclones. This determines the importance of studying hydrometeorological processes not only in the Far East, but also in the South China Sea, and the need for cooperation between Vietnamese and Russian scientists. The main hydrodynamic structure of the western South China Sea is the Vietnamese Coastal Current (Western Boundary current), which depends not only on the seasonal monsoons but also on typhoons. The paper presents the results of joint Russian–Vietnamese studies of the dependence of the vertical structure of the Vietnamese Coastal Current on the Pacific tropical cyclones that form in the South China Sea. The study is done with numerical modeling. The period from April to June 1999 was used for modeling, provided with the necessary field data. The simulation results showed that, in general, the structure of water masses depends on the trajectories of tropical cyclones. In all cases considered, the Vietnamese Coastal Current is not a single flow, but represents a zone of eddy structures of different directions. An exception is the only situation in the condition of a tropical cyclone in the central region of the South China Sea when this current acquired the form of a single continuous flow directed from north to south only in the 200-m layer. The general patterns of changes in the dynamic structure of the Vietnamese Coastal Current for all the considered tropical cyclone trajectories include the following: areas with water transport in the northern direction prevail on the surface, while the rest of the water mass continues to flow generally in the southern direction. This transport of surface waters may be due to the influence of the emerging summer monsoon, and the rest of the water mass, which is less exposed to the still weak atmospheric processes of the monsoon type, continues to flow in the winter regime.

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Runoff generative process and runoff yield from arid talus mantled slopes   总被引：3，自引：0，他引：3  

A. Yair  H. Lavee 《地球表面变化过程与地形》1976,1(3):235-247

Previous works dealing with the influence of a stone cover on runoff yield showed that runoff, attributed to the sealing effect of the topsoil by raindrops impact, was negatively related to the per cent of stone cover and stone size. These works were conducted on gentle slopes (3–11·5 degree) with a per cent of stone cover generally lower than 50 per cent, and composed of gravels. The present study deals with the runoff yield of steep talus slopes (26–36 degree) whose per cent of stone cover is very high (90–100 per cent), composed of cobbles and boulders. Three stimulated rainstorms were performed at various rainfall. intensities and durations on each one of six plots representative of the North eastern sector of Sinai. Although the contiguous stony cover prevented surface sealing by raindrops impact, runoff developed quite quickly on most slopes, and reached at peak discharge, after approximately ten minutes, up to 56 per cent of the rainfall. Differences between plots, in time lag, peak discharge and other hydrological variables, could be attributed mainly to the properties of the upper stony layer, with stone size as the most influential factor. Contrary to previous works, a positive relationship, was obtained between stone size to runoff yield. The result is explained by the process of water concentration. Each cobble and boulder behaves, on a smaller scale, like a bare rocky surface and yields per unit area water amounts beyond the infiltration rate of the limited uncovered areas. For a given stony cover the effect of water concentration is quicker with the big blocks than with gravels. A series of graphs trying to relate theoretically the relative importance of sealing and water concentration processes in runoff generation, at various conditions of stone cover and stone size, is proposed. The graphs enable to reconcile the results of the present study with those of previous works.  相似文献   

APPLICATIONS OF SPATIAL ANALYSIS TECHNIQUES FOR ASSESSING THE CONTRIBUTION OF CLOUD SEEDING TO RAINFALL IN ISRAEL     

Yair Goldreich 《自然地理学》2013,34(6):573-593

The paper summarizes two decades of fitting existing techniques and developing new spatial methods in order to aid the cloud seeders in proving or disproving the value of deliberate rainfall augmentation in Israel. While the spatial regression and the distance correlation matrix (DISTCORMAT) techniques served to distinguish between deliberate rainfall enhancement and inadvertent urban climate modification, the composite correlation map revealed an increase of rainfall duration and an extension of the rainfall target area. Hydrological parameters were utilized to assess the effect of cloud seeding on water resources. Indirectly, the hydrological evidence supported the positive effect of the cloud seeding. Those findings also suggest that cloud seeding augments the rainfall intensity, but interpretation of the composite correlation map does not support this notion. [Key words: cloud seeding, spatial analysis techniques, DISTCORMAT technique, composite correlation map, multiple regression analysis, hydrological parameters, Israel.]  相似文献   

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign     

E. Greenberg  C. Price  Y. Yair  C. Haldoupis  O. Chanrion  T. Neubert 《Journal of Atmospheric and Solar》2009,71(12):1254-1266

During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3–3000 Hz) and broadband very low frequency (VLF: 3–30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites.The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods.Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.  相似文献   

Interspecific Competition between Tetrachthamalus oblitteratus and Tetraclita squamosa     

Yair  Achituv 《Marine Ecology》1981,2(3):241-244

Abstract. Direct evidence for interspecific competition between Tetrachthamalus oblitteratus and Tetraclita squamosa is provided. Tetrachthamalus oblitteratus is smothered and eliminated from the main midlittoral zone by encrusting Tetraclita. The disjunct distribution of Tetrachthamalus can be explained by elimination through competitive exclusion.  相似文献   

Seepage of methane at Jaco Scar,a slide caused by seamount subduction offshore Costa Rica     

Susan Mau  Gregor Rehder  Heiko Sahling  Tina Schleicher  Peter Linke 《International Journal of Earth Sciences》2014,103(7):1801-1815

Methane (CH₄) concentrations and CH₄ stable carbon isotopic composition ( \( \delta^{13} {\text{C}}_{{{\text{CH}}_{4} }} \) ) were investigated in the water column within Jaco Scar. It is one of several scars formed by massive slides resulting from the subduction of seamounts offshore Costa Rica, a process that can open up structural and stratigraphical pathways for migrating CH₄. The release of large amounts of CH₄ into the adjacent water column was discovered at the outcropping lowermost sedimentary sequence of the hanging wall in the northwest corner of Jaco Scar, where concentrations reached up to 1,500 nmol L^?1. There CH₄-rich fluids seeping from the sedimentary sequence stimulate both growth and activity of a dense chemosynthetic community. Additional point sources supplying CH₄ at lower concentrations were identified in density layers above and below the main plume from light carbon isotope ratios. The injected CH₄ is most likely a mixture of microbial and thermogenic CH₄ as suggested by \( \delta^{13} {\text{C}}_{{{\text{CH}}_{4} }} \) values between ?50 and ?62 ‰ Vienna Pee Dee Belemnite. This CH₄ spreads along isopycnal surfaces throughout the whole area of the scar, and the concentrations decrease due to mixing with ocean water and microbial oxidation. The supply of CH₄ appears to be persistent as repeatedly high CH₄ concentrations were found within the scar over 6 years. The maximum CH₄ concentration and average excess CH₄ concentration at Jaco Scar indicate that CH₄ seepage from scars might be as significant as seepage from other tectonic structures in the marine realm. Hence, taking into account the global abundance of scars, such structures might constitute a substantial, hitherto unconsidered contribution to natural CH₄ sources at the seafloor.  相似文献   

Non-linear stochastic galaxy biasing in cosmological simulations     

Rachel S. Somerville  †  Gerard Lemson  Yair Sigad  Avishai Dekel  Guinevere Kauffmann  Simon D. M. White 《Monthly notices of the Royal Astronomical Society》2001,320(3):289-306

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Spatial distribution of surface conditions and runoff generation in small arid watersheds, Zin Valley Badlands, Israel     

Nikolaus J. Kuhn  Aaron Yair   《Geomorphology》2004,57(3-4):183-200

High rill density may be regarded as indicative of frequent and integrated runoff along a drainage network. However, field observations of soil development and rill geometry in small, first-order catchments (0.1 to 1 ha) of the Zin Valley Badlands, northern Negev, Israel, suggest a pattern of partial area contribution and frequent flow discontinuities along hillslopes and channels. Changing soil properties, associated with an increase of slope angle and slope length, appear to be responsible for high infiltration on the slopes, leading to nonuniform runoff generation within small drainage basins. Runoff observation, sprinkling tests, and soil analysis along ridges and sideslopes were carried out to test this hypothesis. The results confirmed that infiltration capacity on the sideslopes is significantly higher than on the ridges. Under current rainfall conditions, only extreme rainfall intensities are sufficient to generate runoff along entire slopes. The discontinuous nature of most runoff events causes erosion on ridges and deposition on slopes, which enhances soil development on the valley sideslopes, creating a positive feedback on infiltration rate and depth. This demonstrates that the links between within-storm rainfall conditions and spatial distribution of soil characteristics have to be incorporated into our understanding of landscape development in badlands.  相似文献   

Arch dam system identification using vibration test data     

S. T. Mau  S. Wang 《地震工程与结构动力学》1989,18(4):491-505

In an effort to study the dynamic characteristics of an arch dam system from the vibration test results, a systematic method of frequency-domain system identification is developed. The governing equations for system identification are based on a non-classical modal superposition method. The non-classical model is shown to be derivable from a general matrix formulation of the dam system. The conventional classical modal formulation becomes a special case of the general non-classical formulation. The modal parameters of the non-classical and the classical formulation are to be identified. The system identification method includes a single-mode sweep procedure for initial parameter estimation and a progressive multiple-mode parameter identification scheme that contains an information criterion for the determination of the optimal number of modes to be included in the identification process. The method is applicable to data measured at more than one point on the dam and to data that include both the amplitude response and the phase response. The method is applied to the vibration test data of two dams. Based on the results of these applications, the adequacy of the classical model and the non-classical model is compared and the effect of the phase data on the parameter determination is discussed.  相似文献   

Tectonics of the Aegean block: Rotation, side arc collision and crustal extension     

Yair Rotstein 《Tectonophysics》1985,117(1-2)

A new tectonic model for the Aegean block is outlined in an effort to explain the widespread extension observed in this region. A key element in this model is the concept of “side arc collision” This term is used to describe the interaction of subducted oceanic lithosphere with continental lithosphere in a subduction arc in which oblique subduction occurs. In the Hellenic arc side arc collision is proposed for the northeast corner near Rhodes. The collision involves subducted African lithosphere, moving to the northeast almost parallel to the arc, with the continental mass of southwest Turkey. It affects the motion of the Anatolian-Aegean plate complex, but is not similar to continental collision since it occurs mostly at depth and involves only little, if any, of the shallow and rigid part of the continental lithosphere. The model assumes that Anatolia and the Aegean are part of one plate complex which undergoes counterclockwise rotation; if it were not for the side arc collision near Rhodes, the two blocks would exhibit similar deformation and might, in effect, be indistinguishable. At present, however, free and undisturbed rotation is possible only for the Anatolian block (excluding western Anatolia) where the motion is accommodated by subduction along the Cyprean arc. Further west the side arc collision inhibits this rotation along the subduction front. Still further west, undisturbed subduction along the central and western parts of the Hellenic arc is again possible and is well documented. On the other side of the Anatolian-Aegean plate complex, relatively free motion occurs along the North Anatolian fault zone including in the Aegean Sea. The combination of this motion in the north with the local obstruction of the rotation near Rhodes, must create a torque and a new pattern of rotation for the western part of the plate complex, thus creating a separate Aegean block. Since, however, the two blocks are not separated by a plate boundary, the Aegean block cannot move freely according to the new torque. Effective motion of the Aegean block relative to Europe and Anatolia, particularly in the north, is achieved through extension of the crust (lithosphere?). Thus the greatest amount of deformation (extension) is observed along the suture zone between the two blocks and, in particular, in the northeastern part of the Aegean block where motion relative to Anatolia must be greatest.  相似文献