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1.
Moche Ziv 《国际地质力学数值与分析法杂志》2003,27(3):207-232
The response of an ideal elastic half‐space to a line‐concentrated impulsive vector shear force applied momentarily is obtained by an analytical–numerical computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. The shear force is concentrated along an infinite line, drawn on the surface of the half‐space, while being normal to that line as well as to the axis of symmetry of the half‐space. An exact loading model is introduced and built into the computational method for this shear force. With this model, a compatibility exists among the prescribed applied force, the geometric decay of the shear stress component at the precursor shear wave, and the boundary conditions of the half‐space; in this sense, the source configuration is exact. For the transient boundary‐value problem described above, a wave characteristics formulation is presented, where its differential equations are extended to allow for strong discontinuities which occur in the material motion of the half‐space. A numerical integration of these extended differential equations is then carried out in a three‐dimensional spatiotemporal wavegrid formed by the Cartesian bicharacteristic curves of the wave characteristics formulation. This work is devoted to the construction of the computational method and to the concepts involved therein, whereas the interpretation of the resultant transient deformation of the half‐space is presented in a subsequent paper. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Yehouda Enzel Revital Bookman David Sharon Haim Gvirtzman Uri Dayan Baruch Ziv Mordechai Stein 《Quaternary Research》2003,60(3):263-273
The Dead Sea is a terminal lake of one of the largest hydrological systems in the Levant and may thus be viewed as a large rain gauge for the region. Variations of its level are indicative of the climate variations in the region. Here, we present the decadal- to centennial-resolution Holocene lake-level curve of the Dead Sea. Then we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare modern natural lake-level variations and instrumental rainfall records and quantify the hydrology relative to lake-level rise, fall, or stability. To quantify that relationship under natural conditions, rainfall data pre-dating the artificial Dead Sea level drop since the 1960s are used. In this respect, Jerusalem station offers the longest uninterrupted pre-1960s rainfall record and Jerusalem rains serve as an adequate proxy for the Dead Sea headwaters rainfall. Principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr−1 average isohyet during 1940–1990 are largely synchronous and in phase (70% of the total variance explained by PC1). This station also represents well northern Jordan and the area all the way to Beirut, Lebanon, especially during extreme drought and wet spells. We (a) determine the modern, and propose the past regional hydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multiyear episodes of Dead Sea level falls/rises and (b) determine that EM cyclone tracks were different in average number and latitude in wet and dry years in Jerusalem. The mean composite sea level pressure and 500-mb height anomalies indicate that the potential causes for wet and dry episodes span the entire EM and are rooted in the larger-scale northern hemisphere atmospheric circulation. We also identified remarkably close association (within radiocarbon resolution) between climatic changes in the Levant, reflected by level changes, and culture shifts in this region. 相似文献
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U. Dayan B. Ziv A. Margalit E. Morin D. Sharon 《Theoretical and Applied Climatology》2001,69(1-2):103-122
Summary At times, a pronounced trough of low barometric pressure extends from equatorial Africa northward, over the Red Sea and the
eastern Mediterranean countries, i.e., the Red Sea Trough. The associated weather is usually hot and dry, and consequently
the atmosphere becomes conditionally unstable. In cases in which additional moisture is supplied and dynamic conditions become
supportive, as the case analyzed here, intense thunderstorms occur, with extreme rain rates, hail and floods.
The storm herein analyzed caused extensive damage both in casualties and property and evolved in two main consecutive phases:
In the first a Mesoscale Convective System that moved from Sinai northward over Israel dominated, and in the second deep convection
was organized mainly along a cold front.
Data analysis indicates several synoptic-scale factors that had a supportive effect on the storm formation and intensification:
Conditional instability established by the Red Sea trough, mid-level moisture transport from Northern Africa, and upper-level
divergence imparted by both polar and subtropical jet streams over the Middle-East.
Mesoscale features were further investigated by means of a hydro-meteorological observational analysis with high spatio-temporal
resolution using raingauge and radar data, and satellite imagery. It is shown that local factors, particularly topographic
effects, play a major role in the evolution, intensity and spatial organization of the convective activity.
Our findings support results of a numerical study of another autumn rainstorm associated with the Red Sea trough. In the present
case we identify an additional contributing factor, i.e., a mid-latitude upper-level trough that further intensified the storm
as it was approaching the Middle-East.
Received July 4, 2000 Revised January 16, 2001 相似文献
5.
B. Ziv 《Theoretical and Applied Climatology》2001,69(1-2):91-102
Summary Cloud bands that extend from the ITCZ along the subtropical jet toward the subtropics are known as ‘tropical plumes’. At
times rainstorms develop at their subtropical edges. One such rainstorm swept eastern North Africa and the Middle East on
23–24 December 1988, with rainfall comparable with the annual averages there. This study examines the storm using the ECMWF
initialized data together with surface observations and satellite imageries.
The analysis indicates that the storm developed at the inflection region ahead of a pronounced trough in the subtropical jet,
with which a mid-latitude trough was merged. Two ageostrophic effects taking place along the jet ahead of the trough contributed
to the intensity of the rainstorm. One was associated with acceleration at the jet entrance, located at tropical latitudes,
which contributed to the enhancement of both tropical convection and the southerly wind component, which enhanced the moisture
tropical transport toward the subtropics. The second was the enhanced near-tropospheric divergence associated with positive
vorticity advection at the inflection region itself.
Since both effects have a quadratic dependence on wind speed, the observed jet speed, 50% larger than its average value, explains
the observed divergence at the inflection point at the 200 hPa level, over 6 × 10−5 s−1, and the vertical velocity at the 700 hPa level, about 10−1 ms−1.
It is suggested here that the merging of a mid-latitude with the trough in the subtropical jet, with which the tropical plume
is associated, is the cause for the intensification of the subtropical jet and hence of its related rainstorms.
Received May 24, 2000 相似文献
6.
Moche Ziv 《国际地质力学数值与分析法杂志》2003,27(3):233-258
The transient deformation of an elastic half‐space under a line‐concentrated impulsive vector shear load applied momentarily is disclosed in this paper. While in an earlier work, the author gave an analytical–numerical method for the solution to this transient boundary‐value problem, here, the resultant response of the half‐space is presented and interpreted. In particular, a probe is set up for the kinematics of the source signature and wave fronts, both explicitly revealed in the strained half‐space by the solution method. The source signature is the imprint of the spatiotemporal configuration of the excitation source in the resultant response. Fourteen wave fronts exist behind the precursor shear wave S: four concentric cylindrical, eight plane, and two relativistic cylindrical initiated at propagating centres that are located on the stationary boundaries of the solution domain. A snapshot of the stressed half‐space reveals that none of the 14 wave fronts fully extend laterally. Instead, each is enclosed within point bounds. These wave arresting points and the two propagating centres of the relativistic waves constitute the source signature. The obtained 14 wave fronts are further combined into 11 disparate wave fronts that are grouped into four categories: an axis of symmetry wave—so named here by reason of being a wave front that is contiguous to the axis of symmetry, three body waves, five surface waves and two inhibitor waves—so named here by reason that beyond them the material motion dies out. Of the three body waves, the first is an unloading shear wave, the second is a diffracted wave and the third is a reflected longitudinal two‐branch wave. Of the two inhibitor waves, the first is a two‐joint relativistic wave, while the second is a two‐branch wave. The wave system, however, is not the same for all the dependent variables; a wave front that appears in the behaviour of one dependent variable may not exist in the behaviour of another. It is evident from this work that Saint–Venant's principle for wave propagation problems cannot be formulated. Therefore, the above results are valid for the particular proposed model for the momentary line‐concentrated shear load. The formulation of the source signature, the wave system, and their role in the half‐space transient deformation are presented here. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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B. Ziv H. Saaroni Y. Yair M. Ganot A. Baharad D. Isaschari 《Theoretical and Applied Climatology》2009,95(3-4):301-310
The factors controlling lightning activity over central Israel and the adjacent Mediterranean Sea were studied. Potential predictors were correlated at 12-h intervals with total number of flashes. Since during the winter season lightning is generated in this region by Cyprus Lows, the data includes 283 observations on days in which this system prevailed for December to February, which covered four winters. The average lightning rate was 26.8 h-1, with a high standard deviation of 55.2 h-1. The total number of flashes at night exceeded the daytime number by 35%, in agreement with previous studies. The CAPE values were on the order of hundreds of J kg-1. A statistical linear multi-regression model was developed for the number of lightning flashes based on 35 atmospheric variables. The correlation between the modeled and the observed number of lightning flashes was 0.67, and 0.81 for the logarithm of the number of lightning flashes (log-lightning). This suggests that the lightning intensity responds exponentially to its governing factors. A linear multi-regression stepwise model for the log-lightning selected seven predictors as significant and yielded a correlation of 0.74. This model was validated by three holdout and three leave-one-out validation experiments. The composition and hierarchy of the significant predictors reflect the dominance of the thermodynamic factors, in particular instability, in determining lightning activity. Though thunderstorms are local or meso-scale phenomena, the synoptic-scale atmospheric variables were found to be powerful predictors for their intensity. 相似文献
9.
Winter synoptic-scale variability over the Mediterranean Basin under future climate conditions as simulated by the ECHAM5 总被引：3，自引：1，他引：2
Christoph Cornelius Raible Baruch Ziv Hadas Saaroni Martin Wild 《Climate Dynamics》2010,35(2-3):473-488
Changes of the winter climate in the Mediterranean Basin (MB) for future A2 conditions are investigated for the period 2071–2100 and compared with the control period 1961–1990. The analysis is based on time-slice simulations of the latest version of the ECHAM model. First, the control simulation is evaluated with reanalysis data. The emphasis is given to synoptic and large-scale features and their variability in the MB. The model is found to be capable of reproducing the main features of the MB and southern Europe in the winter season. Second, the A2 simulation is compared with the control simulation, revealing considerable changes of the synoptic variability. Focusing on the synoptic spatio-temporal scale aims to unfold the dynamic background of the climatic changes. The Mediterranean cyclones, which are individually detected and tracked, decrease by 10% in the Western Mediterranean (WM) whereas no significant change is found in the Eastern Mediterranean. The cyclone intensity is slightly reduced in the entire region. To understand these changes, the underlying dynamical background is analyzed. It is found that changes in baroclinicity, static stability, transformation from eddy kinetic energy to kinetic energy of the mean flow and stationary wave activity are significant in particular in the WM and the coastline of North Africa. The reduction of cyclonic activity severely impacts the precipitation mainly in the southern part of the WM. 相似文献
10.
Summary Continental wind storms are common along the Mediterranean coast. Along the northern coast they are mostly cold, similar
to the Bora or the Mistral, and along the southern coast they are mostly warm, e.g., the Ghibli or the Shirocco. At the eastern
Mediterranean basin and the Levant region, these storms are intermittently warm and cold during the same season and often
even during the same event. Quasi-stationary systems, as well as moving disturbances, are the cause of such wind storms. Accordingly,
the resulting weather conditions may be extremely converse due to the characteristics of the advected airmass. Specific regions
in Israel, sensitive to easterly storms, are influenced by these wind storms for about 10% of the year (e.g., the westerly
slopes of the mountains and valleys with west-east orientation). The frequency, however, of widespread storms covering the
entire region is only approximately 1.4% of the entire year. These wind storms are therefore classified in the present study
according to their climatological and synoptic characteristics; indicating that the dominant synoptic situation is the Red-Sea
trough and the warm advections. These storms appear only from October-May and are most frequent during the cold season. The
diurnal course is characterized by a strengthening in the morning hours and a weakening at noon and in the afternoon hours,
due to the opposing effect of the westerly sea breeze, suppressing the easterly winds and the effect of katabatic winds. Nevertheless,
synoptic conditions may contribute to this tendency as well. Accordingly, a significant increase in the frequencies of easterly
storms, in relation to distance from the seashore has been identified. Although most of the stormy days are with westerly
winds, the easterly wind storms has vast environmental implications, creating damage especially to agriculture and occasionally
also to property and life; coastal flooding, potential air pollution, intensifying of forest fires and occasionally dust and
sand storms.
Received September 9, 1996 Revised March 6, 1997 相似文献