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471.
Timothy N. Stockdale David L. T. Anderson Magdalena A. Balmaseda Francisco Doblas-Reyes Laura Ferranti Kristian Mogensen Timothy N. Palmer Franco Molteni Frederic Vitart 《Climate Dynamics》2011,37(3-4):455-471
The latest operational version of the ECMWF seasonal forecasting system is described. It shows noticeably improved skill for sea surface temperature (SST) prediction compared with previous versions, particularly with respect to El Nino related variability. Substantial skill is shown for lead times up to 1?year, although at this range the spread in the ensemble forecast implies a loss of predictability large enough to account for most of the forecast error variance, suggesting only moderate scope for improving long range El Nino forecasts. At shorter ranges, particularly 3?C6?months, skill is still substantially below the model-estimated predictability limit. SST forecast skill is higher for more recent periods than earlier ones. Analysis shows that although various factors can affect scores in particular periods, the improvement from 1994 onwards seems to be robust, and is most plausibly due to improvements in the observing system made at that time. The improvement in forecast skill is most evident for 3-month forecasts starting in February, where predictions of NINO3.4 SST from 1994 to present have been almost without fault. It is argued that in situations where the impact of model error is small, the value of improved observational data can be seen most clearly. Significant skill is also shown in the equatorial Indian Ocean, although predictive skill in parts of the tropical Atlantic are relatively poor. SST forecast errors can be especially high in the Southern Ocean. 相似文献
472.
Seismic analysis of deep tunnels in near fault conditions: a case study in Southern Italy 总被引:1,自引:0,他引:1
Mirko Corigliano Laura Scandella Carlo G. Lai Roberto Paolucci 《Bulletin of Earthquake Engineering》2011,9(4):975-995
The importance of underground structures in transportation and utility networks makes their vulnerability to earthquakes a
sensitive issue. Underground facilities are usually less vulnerable to earthquakes compared to above-ground structures, but
the associated risk may be relevant, since even a low level of damage may affect the serviceability of a wide network. Seismic
analysis of tunnels close to seismogenic faults is a complex problem, which is often neglected at the design stage for the
lack of specific codes or guidelines for the design of underground structures in seismic conditions and also because, as mentioned
above, underground structures are considered less vulnerable to earthquake loading. This paper investigates the seismic response
of deep tunnels focusing on the required steps for a proper design under both static and dynamic loading. The study aims at
contributing to improve the methods currently used for the seismic analysis of underground structures. At this purpose, the
seismic response of a deep tunnel in Southern Italy has been investigated along the transversal direction. The infrastructure
is part of the railway switch line connecting Caserta to Foggia in the Southern Apennines which is one of the most active
seismic regions in Italy. The seismic response in the transversal direction has been analysed by using the pseudo-static approach
as well as through advanced numerical modeling using the spectral element method coupled with a kinematic approach for finite
fault simulations. The pseudo-static approach has been implemented using a closed-form analytical solution. The results obtained
from advanced numerical modeling and the pseudo-static method have been compared to assess their validity and limitations. 相似文献
473.
A large landslide occurred at Maierato (Vibo Valencia District), Southern Italy, on 15 February 2010, when rapid failure was produced after several days of preliminary movements. The landslide can be classified as a rotational slide with flowing of the mass. It occurred within a larger deep-seated gravitational movement area and was preconditioned for failure by the intrinsic geological weakness of the area. Actually, the in situ survey showed the presence of several ancient movement surfaces all around the urban area. The landslide-triggering factor was the increase in the groundwater flow, consequent to a period of heavy and prolonged rainfall. The aim of the paper is to explain the mechanism of occurrence of the February 2010 composite landslide, in order to assess the landslide hydrogeological susceptibility in the whole urban area of Maierato. For this reason, the present paper deals with: (1) identification of the landslide mechanism and triggering factors (2) slope stability back-analysis using a finite-difference-based shear strength reduction method, and (3) 3D groundwater flow modelling extended to the whole urban area both in pre- and post-failure conditions. The results show that the February 2010 composite landslide was triggered by a water table increase of about 15 m uphill the landslide scarp. This hydrogeological condition could be reached after the period of heavy and prolonged rainfall preceding the landslide event. Finally, based on the groundwater modelling in post-failure condition, a landslide hydrogeological susceptibility map was drawn for the all urban area of Maierato, showing the presence of extended areas exposed to hazard. 相似文献
474.
Conservative tracer experiments can provide information useful for characterizing various subsurface transport properties. This study examines the effectiveness of three different types of transport observations for sensitivity analysis and parameter estimation of a three-dimensional site-specific groundwater flow and transport model: conservative tracer breakthrough curves (BTCs), first temporal moments of BTCs (m 1), and tracer cumulative mass discharge (M d) through control planes combined with hydraulic head observations (h). High-resolution data obtained from a 410-day controlled field experiment at Vandenberg Air Force Base, California (USA), have been used. In this experiment, bromide was injected to create two adjacent plumes monitored at six different transects (perpendicular to groundwater flow) with a total of 162 monitoring wells. A total of 133 different observations of transient hydraulic head, 1,158 of BTC concentration, 23 of first moment, and 36 of mass discharge were used for sensitivity analysis and parameter estimation of nine flow and transport parameters. The importance of each group of transport observations in estimating these parameters was evaluated using sensitivity analysis, and five out of nine parameters were calibrated against these data. Results showed the advantages of using temporal moment of conservative tracer BTCs and mass discharge as observations for inverse modeling. 相似文献
475.
Laura Turconi Sunil Kumar De Francesca Demurtas Luca Demurtas Bruna Pendugiu Domenico Tropeano Gabriele Savio 《Environmental Earth Sciences》2013,69(5):1509-1521
On 6 December 2004, the Villagrande Strisaili area (middle-east Sardinia), was struck by debris flows; 330 mm of rainfall took place within 3 h with an hourly intensity of 120 mm, which is far more above than normal for the study area. In the urban center stony and driftwood deposits accounted for a total volume estimated as 10,000 m3. The event claimed huge amount of infrastructural loss and two human lives. According to the chronicle reports, the area experienced two debris-flow events in the last century. The present paper is the outcome of an intensive study of such debris-flow events including their physical processes and geomorphological effects through both field survey and laboratory analysis. 相似文献
476.
The lowlands of eastern and northeastern Bolivia are characterized by a transition between the humid evergreen forests of the Amazon Basin and the deciduous thorn-scrub vegetation of the Gran Chaco. Within this landscape lies one of the world’s best preserved areas: the ecoregion known as the Chiquitano dry forest, where deforestation patterns over a 30 year period were analyzed. Results indicate that the area of the natural cover was reduced from 97.21 % before 1976 to 82.10 % in 2008, causing significant change in the landscape, especially in the spatial configuration of forest cover. The density of forest fragments increased from 0.073 patches per 100 ha before 1976 to 0.509 in 2008, with a mean distance between patches of 151 and 210 m over the same period, leading to a considerable reduction in the fragment sizes, from 1,204 ha before 1976 to a mere 54 in 2008. This pattern, observed in forests, does not occur in the savannas because, on one hand the savanna area is much lower compared to that of forests, and on the other because the deforestation process tended to be concentrated within forested areas. Based on the observed patterns, it is possible that in the future the natural landscapes will be substituted principally by anthropic landscapes, if there is no change in the economic and land distribution policies. If this process continues, it will stimulate the expansion of mechanized agriculture and the colonization of new areas, which will lead to further deforestation and landscape fragmentation. 相似文献
477.
Adriano Ribolini Monica Bini Ilaria Consoloni Ilaria Isola Marta Pappalardo Giovanni Zanchetta Enrique Fucks Laura Panzeri Marco Martini Filippo Terrasi 《Geografiska Annaler: Series A, Physical Geography》2014,96(2):161-176
This paper investigates several wedge structures formed in continental deposits covering marine sediments deposited during MIS 5 along the central Patagonian coast of Argentina. The size and surface microtexture characteristics of the infilling sediments are consistent with a depositional environment dominated by aeolian transport. Fragments of Andean volcanic rocks (glass shards) in the wedge‐fill suggest long‐distance transport via a westerly component of wind direction. The wedges are interpreted as products of deep seasonal frost action in frozen ground, which produced open cracks that filled rapidly with partially non‐local aeolian sediments. Many wedges cross cut carbonate crusts that formed under permafrost conditions in coastal Patagonia. The radiocarbon dating of carbonate crusts yielded an age of 25–27 kyr bp , while wedge‐fill sediments are OSL dated to 14 670 ± 750 yr bp . This indicates that ground wedge formation occurred during a cold event (the Antarctic Cold Reversal period) that interrupted the permafrost degradation following the Last Glacial Maximum. 相似文献
478.
A two-dimensional pedestrian navigation solution aided with a visual gyroscope and a visual odometer 总被引:1,自引:1,他引:0
Laura Ruotsalainen Heidi Kuusniemi Mohammad Zahidul H. Bhuiyan Liang Chen Ruizhi Chen 《GPS Solutions》2013,17(4):575-586
Integration of different positioning systems such as wireless local area networks (WLAN) and INS has proven to be the most promising approach for navigation in global navigation satellite system challenging environments. However, the integrated solution suffers from the errors induced by the sensors in the INS and the low availability and infrastructure dependency of the WLAN. Visual aiding is a complementary method for augmenting these systems, because it suffers from errors and availability problems of a different nature. We introduce the concept of a “visual gyroscope” and a “visual odometer,” based on recovering user information by tracking the feature motion between consecutive images. All calculations are of sufficiently low complexity to be adoptable for navigation with current smartphones. The camera orientation is observed using the vanishing point locations, and this information is transformed into user heading change information and also used for visual odometer calculations. The visual odometer retrieves the camera translation information based on a special camera configuration and the motion of the matched scale-invariant feature transform features. The performance of both of these tools is evaluated. Experiments in selected environments have proven that visual aiding with a visual gyroscope and visual odometer improves the two-dimensional navigation solution significantly. 相似文献
479.
Laura R. Barraclough 《The Professional geographer》2013,65(2):164-186
This article draws from the recent relational turn in geography to develop a model of relational racialization. It argues that racism functions through the legal and discursive production of linked, interdependent, and unequal places. By comparing two social movements in Los Angeles, the South Central Farmers and the Shadow Hills homeowners, I examine two spatial discourses through which race is relationally reproduced: unequal abilities to mobilize the entitlements of “property rights” and unequal claims to represent hegemonic forms of local heritage. When materialized and naturalized in land use policy, these discourses re-create racial disparities in wealth and poverty and reproduce the qualitative nature of the physical places on which racism depends. 相似文献
480.
Scholars have long documented widespread aging and depopulation of rural communities in the Great Plains. Paralleling these trends is the emergence, growth, and spatial dispersion of new and longtime non-white populations across the region. The dual processes of population loss in many counties combined with the growth of new, non-white population groups suggest that the ethnic structure of the population is changing. In this article we utilize choropleth maps, Hoover and Simpson indexes, and cluster analysis to assess whether the emergence and growth of ethnic minority groups in the Great Plains between 1970 and 2008 is a localized phenomenon or region-wide shift in the ethnic composition of the population. Results suggest that as depopulation is occurring in many counties of this region, the growth of non-white populations, both immigrant and native born, is changing or restructuring the ethnic composition of the Great Plains. 相似文献