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201.
Jonathan S. Friedman Craig A. Tepley Shikha Raizada Qihou H. Zhou Jonas Hedin Rubn Delgado 《Journal of Atmospheric and Solar》2003,65(16-18):1411-1424
We have developed a lidar to study the temperature structure of the nighttime mesopause region over the Arecibo Observatory (18.35°N, 66.75°W) by measuring the lineshape of the fluorescence spectrum of atomic potassium that is deposited in the mesosphere and lower thermosphere (MLT) by meteors. To demonstrate how the potassium lidar can enhance MLT studies at Arecibo, we show recent results for: (1) comparisons with airglow temperature measurements; (2) simultaneous operations with stratospheric and mesospheric temperature profiling by Rayleigh lidar; (3) simultaneous observations of K, Ca+, and E-region electron density profiles; and (4) occurrences of sporadic K layers, and relationships to sporadic E layers. 相似文献
202.
Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years 总被引:4,自引:0,他引:4
Ricardo Villalba Antonio Lara José A. Boninsegna Mariano Masiokas Silvia Delgado Juan C. Aravena Fidel A. Roig Andrea Schmelter Alexia Wolodarsky Alberto Ripalta 《Climatic change》2003,59(1-2):177-232
Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes. 相似文献
203.
v--vIn this study a sensitivity analysis has been carried out by means of the seismic hazard results obtained using the non-zoning methodology (Epstein and Lomnitz, 1966) and the extreme value distribution functions proposed by Gumbel (1958), via a logic tree procedure. The aim of the sensitivity analysis is to identify the input parameters that have the largest impact on assessed hazard and its uncertainty. The research findings from the study of these parameters can serve as a useful guide to facilitate further research studies on seismic hazard evaluations because it allows us to identify parameters that have little or no effect on the seismic hazard results as well as parameters that have great effects on them. In this way, using the obtained results, we have proposed objective criteria in assigning probabilities to the different logic tree branches in a more objective way. It should be noted that, although the sensitivity of the logic tree branches depends on the site, it does not always do so in the same way. Finally, re-evaluation of seismic hazard using the proposed methodology applied to eastern Spain leads to a reduction of uncertainty from 52% to 27% of the expected acceleration with 10% probability of exceedence, at the site with the highest value of seismic hazard (Site 1: Torrevieja). 相似文献
204.
Graeme Hugo 《GeoJournal》2002,56(1):27-37
Australia has a long history of offering protection to refugees. In the post-World War II period it has predominantly been
involved in an offshore refugee settlement program whereby it has assisted international efforts to assist refugees and resettled
almost 600,000 refugees in Australia. In recent years, however, substantial numbers of asylum seekers have arrived on Australia's
shores and this has seen the development of an onshore refugee program which is seen as quite separate from the offshore program.
This has involved the detention of asylum seekers while their claims for protection are assessed and when they are assessed
as being qualified for protection they are given different status to offshore determined refugee settlers. The paper summarises
the development of refugee policy in Australia and the evolution of the offshore and onshore policies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
205.
J. Martinez-FrÍAs A. Delgado M. MillÁN E. Reyes F. Rull D. Travis R. Garcia F. LÓPez-Vera J. A. RodrÍGuez-Losada J. A. Martin-Rubi J. Raya E. Santoyo 《Journal of Atmospheric Chemistry》2005,52(2):185-202
Specific studies about the stable isotope composition (18O/16O and D/H) of atmospheric icy conglomerations are still scarce. The present work offers, for the first time, a very detailed
analysis of oxygen and hydrogen isotopic signatures of unusually large ice conglomerations, or “megacryometeors”, that fell
to the ground in Spain during January 2000. The hydrochemical analysis is based on the bulk isotopic composition and systematic
selective sampling (deuterium isotopic mapping) of eleven selected specimens. δ18O and δD (V-SMOW) of all samples fall into the Meteoric Water Line matching well with typical tropospheric values. The distribution
of the samples on Craig's line suggests either a variation in condensation temperature and/or different residual fractions
of water vapour (Rayleigh processes). Three of the largest megacryometeors exhibited unequivocally distinctive negative values
(δ18O = −17.2%0 and δD = −127 %0 V-SMOW), (δ18O = −15.6%0 and δD = −112%0 V-SMOW) and (δ18O = −14.4%0 and δD = −100%0 V-SMOW), suggesting an atmospheric origin typical of the upper troposphere. Theoretical calculations indicate that the vertical
trajectory of growth was lower than 3.2 km. During the period in which the fall of megacryometeors occurred, anomalous atmospheric
conditions were observed to exist: a substantial lowering of the tropopause with a deep layer of saturated air below, ozone
depression and strong wind shear. Moreover, these large ice conglomerations occurred during non-thunderstorm conditions, suggesting
an alternative process of ice growth was responsible for their formation. 相似文献
206.
207.
208.
Based on a non-linear dam-reservoir interaction model, a study investigating the earthquake response of concrete gravity dams is presented. For the propagation of cracks in unreinforced mass concrete, a discrete crack approach formulation based on the finite element method is applied. A special crack element is used to follow a fictitious crack in order to account for a zone of microcracks developing at the crack tip. The reservoir is modelled using the boundary element method. At a fictitious boundary dividing the irregular finite part of the reservoir from the regular infinite part, the loss of energy due to pressure waves moving away towards infinity is taken into account rigorously. Analyses are performed on the tallest non-overflow monolith of the Pine Flat Dam located in Kern County, California. The interaction of a dam, which may exhibit cracks in mass concrete, with a reservoir domain of arbitrary geometry extending to infinity is studied. Some main parameters are investigated. The importance of tools capable of handling the non-linear dam-reservoir interaction is emphasized. 相似文献
209.
Paleomagnetic evidence for large en-bloc rotations in the Eastern Alps during Neogene orogeny 总被引:2,自引:0,他引:2
We present new paleomagnetic data from the Northern Calcareous Alps and the Central Alps of Austria. All new data are overprint magnetizations and can be subdivided into two groups: In rocks older than earliest Rupelian, two remagnetizations reflecting both clockwise and counter-clockwise rotation were detected. In rocks of late Rupelian and younger ages, only a counter-clockwise rotated remagnetization was found. Our results together with results from previous paleomagnetic studies from the Eastern and Southern Alps suggest two main phases of vertical axis rotation. The first, clockwise rotation affecting the Northern Calcareous Alps was active between earliest to Late Rupelian. We propose a model where the Northern Calcareous Alps are segmented into individual blocks. Within a dextral shear corridor these blocks rotated clockwise due to the counter-clockwise rotation of the Southern Alps and Central Alps. The second, counter-clockwise rotation occurred in the Late Oligocene to Middle Miocene, affecting Eastern and Southern Alps. In this stage of orogeny, the internal massifs of the Western Alps were already accreted to the upper plate and therefore included in counter-clockwise rotation. This rotation is contemporaneous with counter-clockwise rotation in the Apennines and opening of the Balearic basin, and a genetic relationship is suggested. A second step of counter-clockwise rotation, reconstructed from published data, is observed in the sedimentary basins at the southeastern margin of the Eastern Alps, where counter-clockwise rotated Miocene and Pliocene sedimentary rocks are present. This rotation is seen in connection to a young counter-clockwise rotation of the Adriatic plate. 相似文献
210.
Granite fines are inorganic wastes produced in the elaboration of dimension stone. Because of the increasing development of that industry in NW Spain, some concerns related to their classification as type of waste and their environmental impact have been raised. We have performed a detailed physicochemical, mineralogical and geomechanical characterization of the fines and the results make up the basis of several modeling exercises addressed to give answers to particular topics: the impact of high pH waters on the environment and the mobility of some toxic metals. Based on our analyses, we conclude that granite fines do not constitute a significant hazard to the quality of natural waters. 相似文献