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81.
J. B. R. Loureiro D. V. Soares J. L. A. Fontoura Rodrigues F. T. Pinho A. P. Silva Freire 《Boundary-Layer Meteorology》2007,122(2):343-365
The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction
of flows over two-dimensional, smooth, steep hills. Four different law of the wall formulations are tested when a large recirculating
region is formed on the lee side of the hill. Numerical implementation of the near-wall functions was made through a finite
elements code. The standard κ–ε model was used to close the averaged Navier–Stokes equations. Results are validated through
original data obtained in a water tank. Measurements resorted to laser Doppler anemometry. The experiment provide detailed
data for the characterization of the reverse flow in the region between the separation and the reattachment points, with emphasis
on the near wall region. The experimental wall shear stress distribution is compared with the results provided by the different
laws of the wall showing good agreement. The numerical predictions are shown to vary markedly between different formulations. 相似文献
82.
The Influence of the North Atlantic Oscillation on Rainfall Triggering of Landslides near Lisbon 总被引:1,自引:0,他引:1
Ricardo?M.?TrigoEmail author José L.?Zêzere Maria?L.?Rodrigues Isabel?F.?Trigo 《Natural Hazards》2005,36(3):331-354
The majority of landsliding episodes in the area north of Lisbon are associated with rainfall events of short (less than 5
days) medium (5–20 days) or long duration (more than 20 days). The precipitation regime in Portugal is highly irregular, with
large differences between wet and dry years. We have assessed the impact of the North Atlantic Oscillation (NAO) on both the
winter precipitation and the timing and magnitude of associated landslide events. Results show that the large inter-annual
variability of winter precipitation is largely modulated by the NAO mode. The precipitation composite corresponding to high
NAO index presents a considerable lower median value (47 mm/month) than the corresponding low NAO index class (134 mm/month).
The entire precipitation distribution associated with the low NAO index composite encompasses a wider range of values than
the corresponding high NAO index composite. This non-linear behavior is reflected in the probability of occurrence of a very
wet month (precipitation above the 90% percentile) that is just 1% for the positive NAO class and 23% for low NAO index months.
Results for the low NAO class are crucial because these months are more likely associated with long-lasting rainfall episodes
responsible for large landslide events. This is confirmed by the application of a 3-month moving average to both NAO index
and precipitation time series. This procedure allowed the identification of many months with landslide activity as being characterized
by negative average values of the NAO index and high values of average precipitation (above 100 mm/month). Finally, using
daily data we have computed the return periods associated with the entire set of landslide episodes and, based on these results,
obtained a strong linear relationship between critical cumulative rainfall and the corresponding critical rainfall event duration. 相似文献
83.
84.
Luis Ricardo Lage Rodrigues Francisco Javier Doblas-Reyes Caio Augusto dos Santos Coelho 《Climate Dynamics》2014,42(3-4):597-616
Different combination methods based on multiple linear regression are explored to identify the conditions that lead to an improvement of seasonal forecast quality when individual operational dynamical systems and a statistical–empirical system are combined. A calibration of the post-processed output is included. The combination methods have been used to merge the ECMWF System 4, the NCEP CFSv2, the Météo-France System 3, and a simple statistical model based on SST lagged regression. The forecast quality was assessed from a deterministic and probabilistic point of view. SSTs averaged over three different tropical regions have been considered: the Niño3.4, the Subtropical Northern Atlantic and Western Tropical Indian SST indices. The forecast quality of these combinations is compared to the forecast quality of a simple multi-model (SMM) where all single models are equally weighted. The results show a large range of behaviours depending on the start date, target month and the index considered. Outperforming the SMM predictions is a difficult task for linear combination methods with the samples currently available in an operational context. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, these combination methods showed the capability to improve the forecast reliability and accuracy in a large proportion of cases. For example, the Forecast Assimilation method proved to be competitive against the SMM while the other combination methods outperformed the SMM when only a small number of forecast systems have skill. Therefore, the weighting does not outperform the SMM when the SMM is very skilful, but it reduces the risk of low skill situations that are found when several single forecast systems have a low skill. 相似文献
85.
F. Justino J. Marengo F. Kucharski F. Stordal J. Machado M. Rodrigues 《Climate Dynamics》2014,42(3-4):843-858
A coupled global atmosphere-ocean model is used to study the influence of the Antarctica ice sheet in a configuration that mimics that of the early Miocene on the atmospheric and oceanic circulations. Based on different climate simulations of the present day (CTR) and conducted with distinct Antarctic ice sheet topography (AIS-EXP), it is found that the reduction of the Antarctic ice sheet topography (AIS) induces warming of the Southern Hemisphere and reduces the meridional thermal gradient. Consequently, the atmospheric transient low level eddy heat flux $[(\overline{v^{\prime}T^{\prime}})]$ and the eddy momentum flux $[(\overline{u^{\prime}v^{\prime}})]$ are reduced causing the reduced transport of heat from the mid-latitudes to the pole. The stationary flow and transient wave anomalies generate changes in the SSTs which modify the rate of deep water formation, strengthening the formation of the Antarctic Bottom Water. Substantial changes are predicted to occur in the atmospheric and oceanic heat transport and a comparison between the total heat transport of the atmosphere-ocean system, as simulated by the AIS-EXP and the CTR runs, shows that the reduction of the AIS height leads to reduced Southern Hemisphere poleward and increased equatorward heat transport. These results are in agreement with reduced storm track activities and baroclinicity. 相似文献
86.
87.
Geochemical exploration based on the analysis of indicator minerals (IMs) is becoming increasingly used as an effective method for mineral exploration for many types of mineral deposits. The types of IMs used or recommended for exploration for different types of deposits, their properties suitable for concentrating them, as well as those of other common minerals from which they must be separated are listed. 相似文献
88.
Susana Torno Javier Toraño Mario Menéndez Malcolm Gent 《Environmental Earth Sciences》2011,64(1):73-83
A computational fluid dynamics (CFD) model has been developed to simulate the dispersion of dust generated in blasting located
in limestone quarries. This is a complex phenomenon that has been studied through the use of several digital video recordings
of blasts and dust concentration field measurements by ‘light scattering’ dust collectors. In addition, the subsequent simulation
of the dispersion of the dust cloud by means of multiphase CFD has also been studied. CFD calculations were carried out using
software Ansys CFX 10.0, through transitory models with Lagrangian particle models crossing an Eulerian air continuous phase.
This paper presents results obtained by model simulations where physical barriers are set close to the blasting, with the
aim of decreasing the dust cloud dispersal and the associated environmental impact. 相似文献
89.
Ricardo Cesar Silvia Egler Helena Polivanov Zuleica Castilhos Ana Paula Rodrigues 《Environmental Earth Sciences》2011,64(1):211-222
Mercury, zinc and copper contamination was evaluated in soils and fluvial sediments from an abandoned gold mining site at
Descoberto Municipality (southern Minas Gerais State, Brazil). Metals bioavailability and potential mobility were studied
through physical, chemical and mineralogical characterization, geoaccumulation indexes calculations, mercury speciation and
determination of potentially bioavailable contents of zinc and copper. Values of pH were in the neutral range, while organic
matter concentrations were very low. Mineralogical characterization, in the total samples, indicated the presence of quartz,
kaolinite and gibbsite for all samples. Total mercury, zinc and cooper concentrations were higher than the limits recommended
by Brazilian documents. Geoaccumulations indexes revealed that most of the sediment samples were low to moderately polluted
by zinc and copper, while just one sample was very strongly polluted by mercury. Mercury speciation revealed the predominance
of the elementary form for all samples, and low concentrations for exchangeable, strongly bound and residual fractions. Zinc
and copper behavior was strongly controlled by iron and aluminum concentrations, while their bioavailable contents were very
low in comparison with the total concentrations. 相似文献
90.
Cold seeps have recently been discovered in the Nile deep‐sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNA‐encoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy‐based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea‐associated bacterium is closely related to lucinid symbionts from both deep‐sea and coastal species, whereas the Thyasira‐associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid‐shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus‐like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives. 相似文献