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321.
Atsushi Inagaki Marieta Cristina L. Castillo Yoshimi Yamashita Manabu Kanda Hiroshi Takimoto 《Boundary-Layer Meteorology》2012,142(2):207-222
Instantaneous flow structures “within” a cubical canopy are investigated via large-eddy simulation. The main topics of interest
are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent
organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow
patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m ×
1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as
well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically
modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a
whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent
structures in both the velocity and temperature fields “within” the canopy layer. These structures are much larger than the
cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous
flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing
indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity.
Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum
and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified. 相似文献
322.
Baudouin Raoult Guillaume Aubert Marta Gutiérrez Cristina Arciniegas-Lopez Ricardo Correa 《Earth Science Informatics》2009,2(1-2):63-74
The EU funded SIMDAT project is aimed at applying generic grid technology for the solution of complex application problems in several representative fields including automotive, aerospace, pharmaceutical and meteorology. To satisfy the requirements of the World Meteorological Organization (WMO) and the WMO Information Systems (WIS), the partners in the meteorology activity within SIMDAT (ECMWF, Deutscher Wetterdienst, the UK Met office, EUMETSAT and Météo-France), have developed grid-enabled software that provides generic distributed access to distributed meteorological data repositories via web-based portals, through a series of nodes organized in a mesh network. However, granting access to such an infrastructure, especially considering its fully distributed nature, is a serious challenge and a risk to the security of the overall grid infrastructure. SIMDAT solves this problem by implementing a security model based on a decentralized fine-grained access control mechanism that federates data providers and security issues using the notion of “trust domains”. In this paper we highlight the main features of the SIMDAT grid application and describe its security model in detail. 相似文献
323.
324.
Records of Earth's primitive crust are scarce. Eoarchean (older than 3.6 Ga) banded mafic to felsic gneisses have been discovered in the São Francisco Craton, Brazil, pushing back by over 100 million years the oldest gneisses known to date in South America (3.5 Ga). Zircon U‐Pb data yield rock ages from 3,598 to 3,642 Ma with a few ca. 3.65–3.69 Ga grains suggesting even older rocks in the area. Zircon grains show significantly negative to nearly chondritic initial εHf values and two‐stage model ages from 3.82 to 4.33 Ga, which may indicate the existence of a recycled Hadean to early Eoarchean crust in the region. The felsic gneisses are chemically similar to the low‐pressure Tonalite‐Trondhjemite‐Granodiorite association whereas the mafic gneisses have geochemical signatures that resemble within‐plate basaltic andesite to andesite of Iceland (icelandites). The results are relevant to constrain the composition of Earth's first continental crust. 相似文献
325.
Jeffery Eveland Michael N. Gooseff Derrick J. Lampkin J. E. Barrett Cristina Takacs‐Vesbach 《水文研究》2013,27(20):2864-2875
Snow in the McMurdo Dry Valleys is a potential source of moisture for subnivian soils in a cold desert ecosystem. In a water‐limited environment, enhanced soil moisture is expected to provide more favourable conditions for subnivian soil communities. In addition, snow cover insulates the underlying soil from air temperature extremes. Quantifying the spatial and temporal patterns of seasonal snow accumulation and ablation is necessary to understand these dynamics. Repeat high‐resolution imagery acquired for the 2009–2010 austral summer was used to map the seasonal distribution of snow across Taylor and Wright valleys, Southern Victorialand, Antarctica. An edge detection algorithm was used to perform an object‐based classification of snow‐covered area. Coupled with topographic parameters obtained from a 30‐m digital elevation model, unique distribution patterns were characterized for five regions within the neighbouring valleys. Time lapses of snow distribution in each region provide insight into spatially variable aerial ablation rates (change in area of landscape covered by snow) across the region. A strong coastal to interior gradient of decreasing snow‐covered area was evident for both Taylor and Wright valleys. The surrounding regions of Lake Fryxell, Lake Hoare, Lake Bonney, Lake Brownworth, and Lake Vanda exhibited losses of snow‐covered area of 9.61 km2 (?93%), 1.63 km2 (?72%), 1.07 km2 (?97%), 2.60 km2 (?82%), and 0.25 km2 (?96%), respectively, as measured from peak accumulation in October to mid‐January. Differences in aerial ablation rates within and across local regions suggest that both topographic variation and regional microclimates influence the ablation of seasonal snow cover. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
326.
327.
Cristina Izaguirre Fernando J. Méndez Antonio Espejo Inigo J. Losada Borja G. Reguero 《Climatic change》2013,119(2):277-290
The spatial and temporal variability of extreme wave climate along the Central-South American continent is analyzed. The study evaluates changes in the intensity of extreme significant wave height (SWH) throughout the year over the 1980–2008 period, using a calibrated long-term wave reanalysis database forced with NCEP/NCAR reanalysis. A non-stationary extreme value model, based on monthly maxima with a new approach for long-term trends, has been applied. Results show a common positive trend in the Pacific basin throughout all seasons and a significant decreasing trend pattern in the area of Surinam and north of Brazil, on the Atlantic border (up to ?1.5 cm/year in March–April–May). A higher increase of the extreme wave heights is found in the austral summer (December–January–February) at Tierra de Fuego and the Falkland Islands, reaching 6.5 cm/year (which means 1.82 m for the 28 years studied). Furthermore, the complete reanalysis period (1948–2008) is analyzed in order to compare results with the assimilation data period (1980–2008), resulting in some discrepancies, especially in the Atlantic basin. 相似文献
328.
Effects of climate and density-dependent factors on population dynamics of the pine processionary moth in the Southern Alps 总被引:1,自引:0,他引:1
Giovanni Tamburini Lorenzo Marini Klaus Hellrigl Cristina Salvadori Andrea Battisti 《Climatic change》2013,121(4):701-712
Forest pest populations can fluctuate dramatically in relation to climate and density-dependent factors. Although the distributional range of the pine processionary moth Thaumetopoea pityocampa (Lepidoptera Notodontidae) appears to be expanding northward and upslope with climate warming, the relative importance of climate and endogenous, density-dependent factors has not been clearly documented. We analyzed the population dynamics of the moth using long-term data from two provinces in the Southern Alps (Trento: 1990–2009, Bolzano/Bozen: 1975–2011) to evaluate the relative importance of climate and density-dependent factors as regional drivers. Both summer temperatures and rainfall significantly affected population growth rate, with different outcomes depending on the local conditions. Although previous studies indicated that low winter temperatures have negative effects on insect performance, our analyses did not show any negative effect on the population dynamics. A negative density dependent feedback with a 1-year lag emerged as the most important factor driving the population dynamics in both regions. Potential mechanisms explaining the observed negative density feedback include deterioration of host quality, increased mortality caused by pathogens, and increase of prolonged diapause as an adaptive mechanism to escape adverse conditions. 相似文献
329.
Spatiotemporal distribution of aridity indices based on temperature and precipitation in the extra-Carpathian regions of Romania 总被引:2,自引:2,他引:0
Adina-Eliza Croitoru Adrian Piticar Alexandru Mircea Imbroane Doina Cristina Burada 《Theoretical and Applied Climatology》2013,112(3-4):597-607
In the last decades, droughts are a recurrent phenomena in many regions of the world, especially in the subtropics and mid-latitudes, affecting more and more the society. Aridity indices are often used to identify regions prone to that phenomenon. In this paper, we used data recorded in 30 locations in the extra-Carpathian areas of Romania over the period 1961–2007. The De Martonne aridity index (I DM) and the Pinna combinative index (I P) were employed in order to identify critical areas in the most important agricultural regions of the country. Monthly, seasonal, annual, and winter wheat and maize growing season datasets of I DM and annual values of I P were calculated. The trends were identified using the Mann–Kendall test and Sen’s slope, while ordinary Kriging technique was employed for interpolation. The main findings are that the most vulnerable to semi-aridity are the southeastern regions, especially during the warm period of the year, and that for Romania, the use of I DM is more appropriate compared to I P. 相似文献
330.
Optimal filtering high-resolution seismic reflection data using a weighted-mode empirical mode decomposition operator 总被引:2,自引:0,他引:2
Leonardo Macelloni Bradley Matthew Battista Camelia Cristina Knapp 《Journal of Applied Geophysics》2011,75(4):603-614
Gas-hydrate related processes in deep-water marine settings exist on spatial scales that challenge conventional seismic reflection profiling to successfully image them. The conventional approach to acoustic identification of buried hydrates is to use advanced, cost-prohibitive survey techniques and highly customized software to define subsurface structure wherein compositional changes may be modeled and/or interpreted. This study adopts a different approach derived from recent theoretical advancements in signal processing. The method consists in optimal filtering high resolution, single-channel seismic reflection data using the Empirical Mode Decomposition (EMD). The time series is decomposed in sub-components and the noisy portions are suppressed adopting the technique that we referred as Weighted Mode(s) EMD. The optimal filtering greatly improves the resolution and fidelity of the seismic data set.High Resolution single channel seismic profiles, acquired over a carbonate\hydrates site in the northern Gulf of Mexico, manipulated in such way, show a complex, shallow subsurface, and suggest potential evidence for buried gas hydrates. 相似文献