A severe autumn storm over the middle-east: synoptic and mesoscale convection analysis     

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   

Scaling of fracture length and distributed damage     

Vladimir Lyakhovsky 《Geophysical Journal International》2001,144(1):114-122

  相似文献   

Characterization of a Desert Aquitard— Hydrologic and Hydrochemical Considerations     

Ronit Nativ  Ilan Nissim 《Ground water》1992,30(4):598-606

  相似文献   

A numerical integration of a two-level quasi-geostrophic model with variable Rossby parameter     

Dr. A. Huss 《Meteorology and Atmospheric Physics》1967,16(2-3):105-125

Summary Circulation patterns were obtained from a two-level quasi-geostrophic model, in which the Rossby parameter varied with latitude. The initial basic state was characterized by a constant zonal flow at both reference level. The results we re compared with the pattern obtained in a series of experiments with a similar model, in which the Rossby parameter was assumed to be constant. the initial zonal flow in these experiments was assumed in one case to be constant with latitude, in the second casse to have a symmetrical jet centered on the central latitude, and in the thrid case to have its maximum in the southern half of the region. the results of the experiment with a variable Rossby parameter have the closest resemblance to the patterns observed in the real atmospehre. In particular, during the mature stages of the run, the distribution of the zonallyaveraged eddytransport of momentum corresponded quite well to patterns actually observed in the atmosphere.

---

Zusammenfassung Aus einem quasi-geostrophischen Modell mit breitenabhängigem rossby-Parameter wurden Zirkulationsformen errechnet. Der Anfangszustand war durc eine konstante zonale Strömung in zwei Niveaus charakteriseirt. Die Resultate wurden mit Zirkulationen verglichen, die in einer Reihe von Experimenten mit einem ähnlichen Modell, in dem aber der Rossby-Parameter konstant angenommen war, erhalten worden waren. In einemk dieser Fälle wurde angenommen, daß die ursprüngliche zonale Strömung breitenunabhängig war, in einem anderen fall wurde angenommen, daß die Strömung in einem symmetrischen Jetstream über eine mittleren Breite konzentriert war, und in einem dritten Fall wurden angenommen, daß die zonale Strömung ihr Maximum in der südlichen Hälfte des Bereiches hatte. Die Resultate des Experiments mit dem veränderlichen Rossby-Parameter haben die meiste Ähnlichkeit mit Zirkulationsformen in der wirklichen Atmosphäre. Insbesondere paßt die Verteilung des zonal gemittelten Momentumtransports in den Reifestadien des Versuchs gut zu den tatsächlich in der Atmosphäre beobachteten Zirkulationsformen.

---

Résumé On a calculé les formes de circulation découlant d'un modèle quasigéostrophique dont le paramètres de Rossby dépendaient de la latitude. L'état initial en était caractérisé par un courant zonal constant aux deux niveaux. Lels résultats ont été comparés à ceux d'une série d'essais effectués avec un modèle semblable, mais dans lequel les paramètres de Rossby restaient constants. Dans un de ces cas, on a admis que la circulation zonale initiale ne dépendait pas de la latitude. Dans un deuxième, on a simulé un jet symétriquement à une latitude moyenne. Dans un troisième enfin, on a placè le maximum de la circulation zonale dans la moitié sud de l'espace étudié. Les résultats obtenus en partant des essais basés sur un paramètre de Rossby variable sont les plus semblables aux formes de circulation observées réellement dans l'atmosphère. En particulier, la répartition du transport turbulent de la quantité de mouvement — moyenne zonale calculée au stade de maturité de l'essai — est très voisine des formes de circulation observées réellement dans l'atmosphère.

---

---

With 9 Figures

---

The research reported in this document has been sponsored by the Air Force Cambridge Research Laboratories under Grant AF EOAR 63-108 through the European Office of Aerospace Reasearch (OAR), United States Air Force.  相似文献   

On the stability of a slow deflagration front at the surface of a degenerate star     

A. Braun  R. Z. Yahel 《Astrophysics and Space Science》1980,69(1):217-225

On the surface of a degerate star, a slow nuclear combustion process with a wake of escaping matter can exist. The evolution of this process has been studied by solving the nonadiabatic, time-dependent hydrodynamic equations. It has been found that this flow is almost stationary and is stable against small spherical symmetric perturbations.  相似文献   

Fluid inclusions in diamonds from the Diavik mine, Canada and the evolution of diamond-forming fluids   总被引：3，自引：0，他引：3  

Ofra Klein-BenDavid  Elad S. Izraeli  Oded Navon 《Geochimica et cosmochimica acta》2007,71(3):723-744

The analysis of micro-inclusions in fibrous diamonds from the Diavik mine, Canada revealed the presence of high density fluids (HDFs) that span a continuous compositional range between carbonatitic and saline end-members. The carbonatitic end-member is rich in Na, Ca, Mg, Fe, Ba and carbonate; the saline one is rich in K, Cl and water. In molar proportions, the composition of the saline end-member is: K₃₈Na_7.7Ca_1.8Mg_1.6Fe_1.5Ba_1.9SiO_3.1Cl₄₆(CO₃)_5.5(H₂O)₅₆ and that of the carbonatitic end member is: K₁₅Na₂₁Ca_6.7Mg_8.1Fe_6.2Ba_5.7Si_4.8Ti_1.4Al_1.9O₁₇Cl₂₉(CO₃)₂₉(H₂O)₂₉. The micro-inclusions in one diamond span a narrow range between a silicic end-member (rich in Si, K and water) and a carbonatitic one (rich in Mg, Ca, Fe and carbonate). Its average composition is: K₂₆Na_5.5Ca_13.8Mg_8.3Fe_9.6Ba_0.9P_2.5Si₂₅Ti_1.6Al_3.8Cl_2.5O₈₁(CO₃)₂₉(H₂O)₇₈. Thus, the Diavik diamonds span most of the known compositional range for fluids trapped in diamonds. Based on these data and previous analyses of fluids trapped in diamonds, we discuss possible models for the evolution of diamond-forming fluids. The most plausible model is where carbonatitic-HDFs are parental to all the other compositions. They evolve by fractionation of divalentions- and alkali-carbonates and by immiscible separation into saline- and silicic-HDFs. Each phase continues to evolve separately, crystallizing carbonates, diamond, and accessory silicates, phosphates, halides and more of the immiscible phase. Other processes, like the mixing of evolved fluids with fresh parental carbonatitic fluids, or metasomatic interactions with the wallrock also play a role in the evolution of the HDFs. We also propose that the parental carbonatitic-HDF evolves through fractional crystallization of an alkali-rich, low degree melt that is similar to the high pressure parental melts of kimberlites or lamproites.  相似文献   

Surface properties of stabilizing coastal dunes: combining spectral and field analyses     

NOAM LEVIN  GIORA J. KIDRON†  EYAL BEN-DOR 《Sedimentology》2007,54(4):771-788

The coastal dunes of Israel have been undergoing a process of stabilization since 1948. One of the major features of this process is a change in the surface properties of the dunes – the development of a biological soil crust (BSC), and a change in the properties of the sand grains themselves. In Ashdod, at the southern coastal plain of Israel, sand properties that include the BSC, their fines (silt and clay) content and free iron-oxide (indicating their degree of rubification) have been analysed in detail using field and lab spectroscopy methods. In addition, sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above-mentioned factors. It was found that the BSC over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust, especially in the blue band. The crust was found to be particularly developed in the stable areas (mainly the interdunes) and on the north-facing slopes rather than on the south-facing slopes. A positive correlation was found between the crust fines and chlorophyll content, with stable areas showing more developed BSC. The stable areas showed also a lower albedo and slightly more developed reddish colour, indicating a slightly higher rate of rubification. This study demonstrates that the intensity of sand erosion/deposition rates affects soil properties, with the BSC being the fastest to react to the stabilization process (months to several years), followed by the content of fine particles (several years to a decade), whereas the rubification process is a much weaker marker and may need much longer time periods to develop (decades to centuries).  相似文献   

The cold and wet year 1695 — a contemporary German account     

S. Lindgrén  J. Neumann 《Climatic change》1981,3(2):173-187

After describing briefly some of the outstanding features of the uncommonly cold and wet year 1695, one of the coldest years of the Little Ice Age, an annotated translation is presented of a contemporary review of the unusual weather events of the year in Europe. The original was published in 1702 in Frankfurt am Main, Germany, in vol. XIV of the seriesTheatrum Europaeum. The annotation relates to the historical events of the year that were substantially affected by the weather, events to which rather abstruse references are made in the aforementioned contemporary account. In addition to the fact that the contemporary review describes the uncommon weather conditions of 1695, it appears to be the first extended weather review in history.  相似文献   

Diurnal variation in the spatial structure of rainfall in the Northern Negev desert Israel     

H. Kutiel  Prof. D. Sharon 《Theoretical and Applied Climatology》1981,29(3):239-243

  相似文献   

Fluvial processes and settlement in arid environments     

Prof. Asher P. Schick 《GeoJournal》1979,3(4):351-360

The impact of fluvial geomorphic processes on settlement in deserts is tie d to two conflicting factors: the extreme rarity of geomorphic events on the one hand, and the violence of the geomorphic forces coupled with a minimal resistance to erosion on the other.The unique character of desert floods calls for a careful geomorphic evaluation in the siting of settlements and transportation facilities. On the beneficial sid e, the geomorphic processes involved enable, under some conditions, the local exploitation of floodwaters which percolate in the alluvium of the upper tributaries, as well as the utilization of the hydraulic geometry for estimating discharge characteristics.On a larger scale, human interference often disrupts the delicate quasi-equilbrium between erosion and sedimentation in deserts. Although our poor understanding of many aspects of the mechanism of response makes it difficult to separate the effects from those of climatic changes, enough information is available to document the detrimental effect of inconsiderate management on both the regional and local levels.  相似文献