Numerical Modelling of the Turbulent Flow Developing Within and Over a 3-D Building Array, Part I: A High-Resolution Reynolds-Averaged Navier—Stokes Approach

A study of the neutrally-stratified flow within and over an array of three-dimensional buildings (cubes) was undertaken using simple Reynolds-averaged Navier—Stokes (RANS) flow models. These models consist of a general solution of the ensemble-averaged, steady-state, three-dimensional Navier—Stokes equations, where the k-ε turbulence model (k is turbulence kinetic energy and ε is viscous dissipation rate) has been used to close the system of equations. Two turbulence closure models were tested, namely, the standard and Kato—Launder k-ε models. The latter model is a modified k-ε model designed specifically to overcome the stagnation point anomaly in flows past a bluff body where the standard k-ε model overpredicts the production of turbulence kinetic energy near the stagnation point. Results of a detailed comparison between a wind-tunnel experiment and the RANS flow model predictions are presented. More specifically, vertical profiles of the predicted mean streamwise velocity, mean vertical velocity, and turbulence kinetic energy at a number of streamwise locations that extend from the impingement zone upstream of the array, through the array interior, to the exit region downstream of the array are presented and compared to those measured in the wind-tunnel experiment. Generally, the numerical predictions show good agreement for the mean flow velocities. The turbulence kinetic energy was underestimated by the two different closure models. After validation, the results of the high-resolution RANS flow model predictions were used to diagnose the dispersive stress, within and above the building array. The importance of dispersive stresses, which arise from point-to-point variations in the mean flow field, relative to the spatially-averaged Reynolds stresses are assessed for the building array.     

中国西部地区猎隼(Falco cherrug)繁殖生物学与保护

自2001-2006年,中国科学院与英国鸟类研究中心联合对新疆准噶尔盆地和昆仑山、青海玉树地区、西藏那曲地区的猎隼(Falco cherrug)分布状况与繁殖生态进行深入调查。考察行程上万公里。卫星跟踪显示在俄罗斯、蒙古繁殖的猎隼迁往青藏高原越冬。但是,实地调查表明,在新-青-藏还有一些繁殖种群;繁殖区的海拔高度从600 m,上升至5 200 m。根据观察,猎隼喜欢沿用旧巢,多数巢属于"垃圾巢"。因为高原缺乏合适的巢材,那些人类遗弃的皮管、铁丝、皮带、破布、汽车零件、骨片、绳子等垃圾充斥于巢穴之中。考察期间,共找到100多只猎隼成鸟、约35个猎隼巢或巢区;分布地点涉及昆仑山脉、准噶尔盆地、卡拉麦里山脉、北塔山、可可西里、唐古拉山脉等,包括新疆奇台、且末、青河、塔城,青海楚玛尔河、五道梁、曲麻莱、雁石坪、玉树,西藏安多、那曲等。猎隼巢址多位于悬崖凹陷处(21个)、河岸砂土洞(5)、桥梁(2)等处;巢高于地面7~30 m。通常沿用渡鸦、大鵟、棕尾鵟、金雕的旧巢,有同步繁殖现象。附近有鼠兔、雪雀、地鸦、岩鸽、石鸡、沙鸡等活动。巢区沿着山脉或者丘陵连续分布,巢间距最近2.5 km,通常4~8 km或更远。在准噶尔盆地其繁殖密度1.1~1.6对/1 000 km2。通常4~5月产卵,窝卵数3~5枚;5月上旬和中旬已有部分幼鸟出壳。虽然在中国捕捉猎隼现象十分猖獗,但考察结果依然令人振奋。建议中国猎隼研究小组(CSRG)积极开展国际合作,通过卫星跟踪、GPS定位、电子微芯片标记(PIT)、DNA指纹图谱分析、人工猎隼栖架和巢穴招引技术等,不断完善监测手段和管理机制,为猎隼的保护与合理利用做出努力。     

Methods and results of large scale applications of cloud seeding in the Western United States

Summary During the period 1950–1954, North American Weather Consultants, an applied meteorological consulting group, conducted a number of cloud seeding programs in the Western United States. Over 50,000 hours of silver iodide generator operation were recorded, which is probably one of the largest massive applications of cloud seeding on record. Methods and results of these operations are presented.

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Zusammenfassung Während der Jahre 1950–54 haben die North American Weather Consultants, eine Gruppe von Beratern für angewandte Meteorologie, im Westen der Vereinigten Staaten eine Reihe von Cloud seeding-Programmen durchgeführt. Während mehr als 50.000 Stunden wurde die Wirkungsweise von Silberjodid-Generatoren beobachtet, vermutlich eine der umfangreichsten Anwendungen dieser Methode, die je durchgeführt wurden. Methodik und Ergebnisse dieser Arbeiten werden in der vorliegenden Arbeit behandelt.

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Résumé Pendant les années 1950/54, les «North American Weather Consulttants», groupe d'experts de météorologie appliquée, ont exécuté dans l'Ouest des Etats-Unis une série d'essais d'insémination de nuages. On a observé pendant plus de 50.000 heures l'effet de générateurs à l'iodure d'argent; il s'agit probablement d'une des plus vastes applications du procédé. La présente note traite des méthodes employées et des résultats obtenus.

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With 8 Figures.     

Discovery of cryptotephra at Middle–Upper Paleolithic sites Arma Veirana and Riparo Bombrini,Italy: a new link for broader geographic correlations

Chemical characterization of cryptotephra is critical for temporally linking archaeological sites. Here, we describe cryptotephra investigations of two Middle–Upper Paleolithic sites from north-west Italy, Arma Veirana and Riparo Bombrini. Cryptotephra are present as small (<100 µm) rhyolitic glass shards at both sites, with geochemical signatures rare for volcanoes in the Mediterranean region. Two chemically distinct shard populations are present at Arma Veirana (P1 and P2). P1 is a high silica rhyolite (>75 wt.%) with low FeO (<1 wt.%) and a K₂O/Na₂O > 1 and P2 is also a high silica rhyolite (>75 wt.%) but with higher FeO (2.33–2.65 wt.%). Shards at Riparo Bombrini (P3) are of the same composition as P1 shards at Arma Veirana, providing a distinct link between deposits at both sites. Geochemical characteristics suggest three possible sources for P1 and P3: eruptions from Lipari Island (56–37.7 ka) in Italy, the Acigöl volcanic field (200–20 ka) in Turkey and the Miocene Kirka-Phrigian caldera (18 Ma) in Turkey. Eruptions from Lipari Island are the most likely source for P1,3 cryptotephra. This study highlights how cryptotephra can benefit archaeology, by providing a direct link between Arma Veirana and Riparo Bombrini as well as other deposits throughout the Mediterranean.     

Probabilistic Model for Concentration Fluctuations in Compact-Source Plumes in an Urban Environment

A comprehensive model for the prediction of concentration fluctuations in plumes dispersing in the complex and highly disturbed wind flows in an urban environment is formulated. The mean flow and turbulence fields in the urban area are obtained using a Reynolds-averaged Navier-Stokes (RANS) flow model, while the standard k-ϵ turbulence model (k is the turbulence kinetic energy and ϵ is the viscous dissipation rate) is used to close the model. The RANS model provides a specification of the velocity statistics of the highly disturbed wind flow in the urban area, required for the solution of the transport equations for the mean concentration and concentration variance (both of which are formulated in the Eulerian framework). A physically-based formulation for the scalar dissipation time scale t _d , required for the closure of the transport equation for , is presented. This formulation relates t _d to an inner time scale corresponding to “internal” concentration fluctuation associated with relative dispersion, rather than an outer time scale associated with the entire portion of the fluctuation spectrum. The two lowest-order moments of concentration ( and ) are used to determine the parameters of a pre-chosen functional form for the concentration probability density function (clipped-gamma distribution). Results of detailed comparisons between a water-channel experiment of flow and dispersion in an idealized obstacle array and the model predictions for mean flow, turbulence kinetic energy, mean concentration, concentration variance, and concentration probability density function are presented.     

In situ Raman spectroscopy on kerogen at high temperatures and high pressures

Kerogen samples were treated at temperatures and pressures up to 25–600°C and ~9 GPa, respectively. In situ micro-Raman spectroscopy was used to measure the systematic changes in the first-order Raman spectral features during the process of temperature or pressure increment. Three Raman bands, D1, D2, and G bands, were examined to characterize the structural and chemical changes of kerogen at high temperatures and pressures. We found that the wavenumbers of D1, D2 and G bands showed a linear variation with both temperature and pressure. Therefore, a correlation between R1 and R2 and the peak temperature in regionally metamorphosed rocks cannot be applied to this work. This result implies that the G band may serve as a temperature or pressure indicator during the promotion of maturation of kerogen. Kerogen possesses reversible properties in contrast with the natural samples recovered from the field suffered from prolonged thermal history during regional metamorphism.     

Energy balance in urban Mexico City: observation and parameterization during the MILAGRO/MCMA-2006 field campaign

The parameterization of the energy balance from a residential and commercial neighborhood of Mexico City was investigated using direct measurements of radiative and heat fluxes carried out during the MILAGRO/MCMA-2006 field campaign as a reference. The measured fluxes were used to evaluate different models of the energy balance based on parameterizations that require standard meteorological observations: ambient temperature, relative humidity, atmospheric pressure and cloudiness. It was found that these models reproduce with reasonable accuracy the diurnal features of the radiative and heat fluxes. The largest differences between modeled and observed fluxes correspond to the incoming longwave radiation, mainly due to errors in the cloudiness data. This paper contributes to the understanding of the energy partitioning in (sub)tropical urban environments, particularly in the developing world, where energy balance models have not been evaluated.     

Web 2.0 collaborations address uncertainty in climate reconstructions of the past millennium

Reducing uncertainty in global temperature reconstructions of the past millennium remains the key issue in applying this record to society’s pressing climate change problem. Reconstructions are collaborative, built on the research of hundreds of scientists who apply their diverse scientific expertise and field and laboratory skill to create the individual proxy reconstructions that underlie the multi-proxy, global average temperature time series. Web 2.0 features have enabled collaborative efforts that improve the characterization of uncertainty. Raw data shared via a repository (the World Data Center for Paleoclimatology) enable new reconstructions from the collection of user-generated data. Standards propagated by expert communities facilitate quality control and interoperability. Open access to data and computer code promote transparency and make the science accessible to a broader audience. Blogs, wikis, and listservs share background information and highlight contentious as well as unique aspects of paleo science. A novel approach now underway, titled the Paleoclimate Reconstruction Challenge, and based on the sharing of simulated data (pseudo-proxies) and reconstruction results, seeks to facilitate method development, further reducing uncertainty. Broadly-useful aspects of the Challenge may find application in other fields.     

Beneath the Salt Marsh Canopy: Loss of Soil Strength with Increasing Nutrient Loads

Although the broadly observed increase in nutrient loading rates to coastal waters in the last 100 years may increase aboveground biomass, it also tends to increase soil metabolism and lower root and rhizome biomass—responses that can compromise soil strength. Fourteen different multiyear field combinations of nutrient amendments to salt marshes were made to determine the relationship between soil strength and various nitrogen, phosphorus, and nitrogen+phosphorus loadings. There was a proportional decline in soil strength that reached 35% in the 60- to 100-cm soil layer at the highest loadings and did not level off. These loading rates are equivalent to those in the flow path of the Caernarvon river diversion, a major wetland restoration project near New Orleans; 12% of the wetlands in the flow path were converted to open water in 2005. The increased nutrient loading from the Mississippi River watershed this century has also driven the formation of the low oxygen zone (the “Dead Zone”) that forms off the Louisiana–Texas shelf each summer. These results suggest that improving water quality in the watershed will aid the restoration of both offshore waters and coastal wetland ecosystems.