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排序方式: 共有216条查询结果,搜索用时 15 毫秒
101.
Combining the standardized precipitation index and climatic water deficit in characterizing droughts: a case study in Romania 总被引:1,自引:1,他引:0
Cr. Paltineanu I. F. Mihailescu Zoia Prefac Carmen Dragota Felicia Vasenciuc Nicola Claudia 《Theoretical and Applied Climatology》2009,97(3-4):219-233
This paper characterizes droughts in Romania using the approach of both the standardized precipitation index (SPI) and climatic water deficit (WD). The values of the main climatic factors (rainfall, temperature, reference evapotranspiration, etc.) were obtained from 192 weather stations in various regions of Romania. Penman–Monteith reference evapotranspiration (ETo-PM) was used to calculate WD as the difference between precipitation (P) and ETo-PM. SPI was calculated from precipitation values. There is a clear difference between drought and aridity. Drought occurrence determines higher WD values for plains and plateaus and lower climatic excess water (EW) values for high mountains in Romania, depending on the aridity of the specific region considered and drought severity. WD calculated as mean values for both normal conditions and, for all locations studied, various types of drought was correlated with mean annual precipitation and temperature, respectively. The combined approach of WD and SPI was mainly carried out for periods of 1 year, but such studies could also be done for shorter periods like months, quarters, or growing season. The most arid regions did not necessarily coincide with areas of the most severe drought, as there were no correlations between WD and SPI and no altitude-based SPI zones around the Carpathian Mountains, as is the case for other climate characteristics, soils and vegetation. Water resource problems arise where both SPI values characterize extremely droughty periods and WD values are greatly below ?200 mm/year. This combined use of SPI and WD characterizes the dryness of a region better than one factor alone and should be used for better management of water in agriculture in Romania and also other countries with similar climate characteristics. 相似文献
102.
Carmen J. Nappo 《Boundary-Layer Meteorology》1991,54(1-2):69-87
Breakdowns of stability in the PBL are examined using one-minute average horizontal wind speeds and temperatures observed over many nights at stations located in simple and complex terrain. The analysis is based on the temporal behavior of the wind speed-temperature covariance, which is obtained by digital bandpass filtering. It is shown that breakdowns are a common feature of the stable PBL over both simple and complex environments. Vertical fluxes of heat during breakdowns are estimated to be a significant fraction of the nighttime average heat flux. It is hypothesized that a major portion of the nighttime vertical transfer of heat, momentum, and atmospheric pollutants occurs during periods of stability breakdowns. 相似文献
103.
Eugene T. Premuzic Carmen M. Benkovitz Jeffrey S. Gaffney John J. Walsh 《Organic Geochemistry》1982,4(2):63-77
Existing data on the distribution of organic carbon and nitrogen in marine sediments have been analyzed in order to better understand the physical and chemical processes involved in this aspect of the global carbon cycle. Maps of the global distribution of organic carbon and nitrogen in the sediments of world oceans and seas are presented.Correlation analyses of the available information dealing with the distribution of marine sedimentary organic matter has revealed that in terms of bulk parameters (%COrg and %N Kjeldahl), there is an apparent accumulation of organic matter on the continental slope (water column depth 200–2000 m). Specific interactions between clays and organic matter, although indicated in laboratory experiments, have not been detected by these analyses. 相似文献
104.
Luis M Alva-Valdivia Avto Goguitchaichvili Manuel Grajales Antonio Flores de Dios Jaime Urrutia-Fucugauchi Carmen Rosales Juan Morales 《Comptes Rendus Geoscience》2002,334(11):811-817
We report rock-magnetic and magnetostratigraphic results from one of the best exposed Permo-Carboniferous outcrops in Mexico, in order to determine some decisive magnetostratigraphy constraints. Some spinels, most probably titanomagnetites, seem to be responsible for aimantation, although greigite may also exist judging from thermal desaimantation of isothermal remanence. Remanence analyses indicate that only one remanent component could be recognized with minor secondary overprint, which were easily removed applying 100–180 °C. Six normal and four reverse magnetozones were recognized from bottom to top in Patlanoya section between 340 and 280 Myr. Both normal and reverse polarity rocks were found in Carboniferous time around 340 Myr, in agreement with previous paleomagnetic works. Our record revealed two normal subchrons within PCRS (Kiaman), the dominantly reverse superchron, at 305 and 280 Myr, respectively. These, which may be speculatively correlated to normal aimantation, occasionally occurred during PCRS interval. More detailed studies are needed in order to establish a more precise magnetostratigraphy for Permo-Carboniferous time. To cite this article: L.M. Alva-Valdivia et al., C. R. Geoscience 334 (2002) 811–817. 相似文献
105.
Leonardo Alvarez Julio García Franco Vaccari Giuliano F. Panza Bertha González Carmen Reyes Bárbara Fernández Ramón Pico José A. Zapata Enrique Arango 《Pure and Applied Geophysics》2004,161(5-6):1041-1059
— The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic zoning of the city. Three different main zones are identified, and a small sector characterized by major resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (MS=7), and for the maximum possible (MS=8). 相似文献
106.
Georges Clauzon Jean-Pierre Suc† Speranta-Maria Popescu† Mariana Marunteanu‡ Jean-Loup Rubino¶ Florian Marinescu‡ Mihaela Carmen Melinte§ 《Basin Research》2005,17(3):437-462
A recently published scenario viewing the Messinian salinity crisis as two evaporitic steps rather than one has led to a search for new indices of the crisis in the Eastern Paratethys. Fluvial processes characterized the southwestern Dacic Basin (Southern Romania, i.e. the Carpathian foredeep) whereas brackish sediments were continuously deposited in its northern part. This is consistent with previously evidenced responses of the Black Sea to the Messinian salinity crisis. High sea‐level exchanges between the Mediterranean Sea and Eastern Paratethys are considered to have occurred just before and just after desiccation of the Mediterranean. This accounts for two successive Mediterranean nannoplankton‐dinocyst influxes into the Eastern Paratethys that, respectively, belong to zones NN 11 and NN 12. Meanwhile, two separate events that gave rise to Lago Mare facies (with Paratethyan Congeria, ostracods and/or dinoflagellate cysts) arose in the Mediterranean Basin in response to these high sea‐level exchanges and located 5.52 and 5.33 Ma (isotopic stages TG 11 and TG 5, respectively), i.e. just before and just after the almost complete desiccation of the Mediterranean). These Lago Mare facies formed independently of lakes with ostracods of the Cyprideis group that developed in the central basins during the final stages of desiccation. The gateway faciliting these water exchanges is not completely identified. A proto‐Bosphorus strait seems unlikely. A plausible alternative route extends from the northern part of the Thessaloniki region up to the Dacic Basin and through Macedonia and the Sofia Basin. The expression ‘Lago Mare’ is chronostratigraphically ambiguous and should be discontinued for this purpose, although it might remain useful as a palaeoenvironmental term. 相似文献
107.
Virginia Souza‐Egipsy Jacek Wierzchos Carlos Sancho Anchel Belmonte Carmen Ascaso 《地球表面变化过程与地形》2004,29(13):1651-1661
Sandstone structural landscapes in the semi‐arid Torrollones de Gabarda area (Province of Huesca, NE Spain) are often covered by a well developed biological soil crust of lichens, mosses and cyanobacteria and black coatings on vertical surfaces. By using scanning electron microscopy with backscattered detector imaging, the biological soil crust studied evidenced high activity in the sandstone–crust interface. Processes such as physical disintegration, etching and dwelling as well as biomineralization by calcium oxalate and ?xation of mineral particles by extracellular polymeric substances were observed. On the horizontal sandstone surfaces these processes may cause the occurrence of gnammas and the development of a protective coating that favours intense ?aking when the crust is disturbed. On the sandstone cliffs, columnar and tafoni weathering development is clearly guided by the protective action of the biological soil crust. These qualitative observations are important to develop methodologies to address their quantitative importance in geomorphological processes in semi‐arid landscapes. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
108.
Local Agenda 21 (LA21) is widely regarded as a key tool for implementing sustainability policies since local authorities are closer to ordinary people and some local managers and politicians have the ability to adapt organisations to new managerial atmospheres and social demands. However, local governments tend to lack the right economic, human and knowledge resources. Consequently, in the search for local sustainable development, networking and collaborative approaches to LA21 can help local authorities save resources and share knowledge and best practices. Although both research and politicians have tended to focus on LA21, we believe Regional Agenda 21 (RA21) needs to be emphasised as a complementary tool. This paper examines successful innovative practices in the Basque Autonomous Community (BAC) over a 4-year period, with a view to shedding light on the theoretical literature and to aiding regional and local authorities. Although research on policy networks has produced useful results, we are still some way from a plausible, consensus-based theory of policy networks. Based on experience in the BAC, the present article offers an integrated approach to understanding the antecedents and consequences of a regional knowledge-driven network for LA21 promotion. Although LA21 implementation has been studied before, evidence about networking at regional level is scarce. Other regions in developing countries could use this approach to achieve successful policy networks. 相似文献
109.
Estimation of orographically induced wave drag in the stable boundary layer during the CASES-99 experimental campaign 总被引:1,自引:0,他引:1
This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column
atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to
calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for
the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and
that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify
the wind speed sufficiently to substantially change the surface sensible heat flux. 相似文献
110.
Octavian G. Duliu Carmen Cristache Otilia A. Culicov Marina V. Frontasyeva 《Marine pollution bulletin》2009,58(6):827-831
The vertical distributions of five potential pollutants - Zn, As, Br, Sn, and Sb - were determined via epithermal neutron activation in the upper 50 cm of unconsolidated sediments from the Black Sea, which were collected 600 m below sea surface. This analysis demonstrated increasing concentrations towards the upper limits of sediments, which were greater than alert concentrations in the case of As and Br, and in accordance with Romanian Environment Regulations. The utilization of Chernobyl 137Cs as a time marker allowed for dating of this region to the last 100 years. 相似文献