Dynamo action in the ABC flows using symmetries     

Samuel E. Jones  Andrew D. Gilbert 《地球物理与天体物理流体动力学》2014,108(1):83-116

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大气和植被生态及土壤系统水文过程相互作用的一些研究   总被引：9，自引：1，他引：8  

曾庆存  曾晓东  王爱慧  Robert E. Dickinson  Xubin Zeng  Samuel S.P. Shen 《大气科学》2005,29(1):7-19

利用我国测站的降水资料、卫星测得的OLR和高云量资料、SST和137°E次表层海温资料以及NCEP/NCAR再分析资料,分析了东亚夏季风的爆发和北进的年际变化特征及其与热带西太平洋热状态的关系.分析结果表明:当春季热带西太平洋处于暖状态,菲律宾周围对流活动强,在这种情况下,南海上空对流层下层有气旋性距平环流,西太平洋副热带高压偏东,从而使得南海夏季风爆发早;并且,当夏季热带西太平洋也处于暖状态,菲律宾周围对流活动也很强,在这种情况下,西太平洋副热带高压北进时,在6月中旬和7月初存在明显的突跳,从而使得东亚季风雨带在6月中旬明显由华南北跳到江淮流域,并于7月初由江淮流域北跳到黄河流域、华北和东北地区.这将引起江淮流域和长江中、下游夏季风降水偏少,并往往发生干旱,而黄河流域、华北和东北地区的夏季降水正常或偏多.相反,当春季热带西太平洋处于冷状态,菲律宾周围对流活动弱,在这种情况下,南海上空对流层下层有反气旋性距平环流,西太平洋副热带高压偏西,从而使得南海夏季风爆发晚;并且,当夏季热带西太平洋也处于冷状态,菲律宾周围对流活动也很弱,在这种情况下,西太平洋副热带高压北进时,在6月中旬或7月初向北突跳并不明显,而是以渐进式向北移动,从而使得东亚季风雨带一直维持在长江流域和淮河流域.这将引起此两流域夏季风降水偏多,并往往发生洪涝,而黄河流域、华北和东北地区的夏季降水偏少,发生干旱.作者还从非线性多平衡态动力理论说明了菲律宾周围对流活动强弱对西太平洋副热带高压北进时以突跳或渐进式向北移动起到重要作用.  相似文献   

Non-LTE radiative transfer for sub-millimeter water lines in Comet 67P/Churyumov-Gerasimenko     

Seungwon Lee  Paul von Allmen  Samuel Gulkis 《Icarus》2011,215(2):721-731

The European Space Agency (ESA) Rosetta spacecraft (Schulz, R., Alexander, C., Boehnhardt, H., Glassmeier, K.H. (Eds.) [2009]. “ROSETTA - ESA”) will encounter Comet 67P/Churyumov-Gerasimenko in 2014 and spend the next 18 months in the vicinity of the comet, permitting very high spatial and spectral resolution observations of the coma and nucleus. During this time, the heliocentric distance of the comet will change from ∼3.5 AU to ∼1.3 AU, accompanied by an increasing temperature of the nucleus and the development of the coma. The Microwave Instrument for the Rosetta Orbiter (MIRO) will observe the ground-state rotational transition (1₁₀-1₀₁) of H₂¹⁶O at 556.936 GHz, the two isotopologues H₂¹⁷O and H₂¹⁸O and other molecular transitions in the coma during this time (Gulkis, S. et al., [2007]. MIRO: Microwave Instrument for Rosetta Orbiter. Space Sci. Rev. 128, 561-597).The aim of this study is to simulate the water line spectra that could be obtained with the MIRO instrument and to understand how the observed line spectra with various viewing geometries can be used to study the physical conditions of the coma and the water excitation processes throughout the coma. We applied an accelerated Monte Carlo method to compute the excitations of the seven lowest rotational levels (1₀₁, 1₁₀, 2₁₂, 2₂₁, 3₀₃, 3₁₂, and 3₂₁) of ortho-water using a comet model with spherically symmetric water outgassing, density, temperature and expansion velocity at three different heliocentric distances 1.3 AU, 2.5 AU, and 3.5 AU. Mechanisms for the water excitation include water-water collisions, water-electron collisions, and infrared pumping by solar radiation.Synthetic line spectra are calculated at various observational locations and directions using the MIRO instrument parameters. We show that observations at varying viewing distances from the nucleus and directions have the potential to give diagnostic information on the continuum temperature and water outgassing rates at the surface of the nucleus, and the gas density, expansion velocity, and temperature of the coma as a function of distance from the nucleus. The gas expansion velocity and temperature affect the spectral line width and frequency shift of the line from the rest frequency, while the gas density (which is directly related to the outgassing rate) and the line excitation temperature determine the antenna temperature of the absorption and emission signal in the line profile.  相似文献   

A new look at the phenomenon of offshore pile plugging     

Samuel G. Paikowsky  Robert V. Whitman  Mohsen M. Baligh 《Marine Georesources & Geotechnology》2013,31(3):213-230

Abstract

Open‐pipe piles are widely used for offshore structures. During the initial stage of installation, soil enters the pile at a rate equal to the pile penetration. As penetration continues, the inner soil cylinder may develop sufficient frictional resistance to prevent further soil intrusion, causing the pile to become plugged. The open‐ended pile then assumes the penetration characteristics of a closed‐ended pile. The mode of pile penetration significantly alters the soil‐pile interaction during and after installation. This affects the ultimate static bearing capacity (mainly in granular materials), the time‐dependent pile capacity (in clays), and the dynamic behavior and analysis of the piles.

Following a summary demonstrating the effects of pile plugging, a review of the common view of offshore pile plugging is undertaken. The interpretation of plugging by referring to the average plug length has led to the erroneous conclusion that in most piles significant plugging action does not occur.

Establishment of an analogy between soil samplers and open‐ended piles enabled correct identification of plugging by referring to the incremental changes in plug length. Examination of case histories of plugging of offshore piles revealed that beyond a certain penetration depth‐to‐diameter ratio, most piles are plugged.  相似文献   

Temporal changes of diatoms in marine biofilm developed on acrylic panels submerged in a tropical coast     

Sathianeson Satheesh  Samuel Godwin Wesley 《Ocean Science Journal》2012,47(4):509-517

The colonization of diatom groups on the acrylic panels submerged in Kudankulam coastal waters, east coast of India, was studied for one year from October 2004 to August 2005. Results showed temporal variability in the abundance of dominant diatom groups. Diatoms belonging to 19 genera colonized the panels. Navicula and Nitzschia were the dominant diatoms observed throughout the present study. The abundance of diatoms on test panels increased with the length of exposure. Significant variations in the abundance of Navicula and Nitzschia were observed between the sampling months. Temporal changes in biofilm diatom community composition in this study attain significance from the view point of macrofouling community recruitment on marine structures.  相似文献   

Crystallization history of Obsidian Dome,Inyo Domes,California   总被引：4，自引：0，他引：4  

Samuel E. Swanson  Michael T. Naney  H. R. Westrich  J. C. Eichelberger 《Bulletin of Volcanology》1989,51(3):161-176

Samples obtained by U.S. Department of Energy research drilling at the 600-year-old Obsidian Dome volcano provide the rare opportunity to examine the transition from volcanic (dome) to plutonic (intrusion) textures in a silicic magma system. Textures in the lavas from Obsidian Dome record multiple periods of crystallization initiated in response to changes in undercooling (T) related to variable degassing in the mag-ma. Phenocr)ysts formed first at low T. A drastic increase in T, related to loss of a vapor phase during initial stages of eruption, caused nucleation of microlites. All of the lavas thus contain phenocrysts and microlites. Extrusion and subsequent devitrification of the dry (0.1 wt% H₂O) magma crystallized spherulites and fine-grained rhyolite at high T. A granophyric texture, representing crystallization at a moderate T, formed in the intrusions beneath Obsidian Dome. Textures in the intrusion apparently represent crystallization of hydrous (1–2 wt% H₂O) rhyolitic magma at shallow depths.  相似文献   

Pelmatozoan echinoderms from the Cambrian–Ordovician transition of the Iberian Chains (NE Spain): early diversification of anchoring strategies     

Samuel Zamora  J. Javier Álvaro  Daniel Vizcaïno 《Swiss Journal of Geoscience》2009,102(1):43-55

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A Review of: “Making Population Geography”     

Samuel M. Otterstrom 《The Professional geographer》2013,65(1):147-149

Ryan, James R. Picturing Empire: Photography and theVisualization of the British Empire

Sizoo, Edith (ed.) Women's Lifeworlds: Women's Narratives on Shaping their Realities.

Teaford, Jon Post-Suburbia Government and Politics in the Edge Cities.

Warhus, Mark Another America: Native American Maps and the Historyof Our Land

Yeung, Y. M. and Chu, David K. Y. (eds.) Guangdong: Survey of aProvince Undergoing Rapid Change

Young, E. M. World Hunger  相似文献   

New Methods to Estimate 2D Water Level Distributions of Dynamic Rivers     

Samuel Diem  Philippe Renard  Mario Schirmer 《Ground water》2013,51(6):847-854

River restoration measures are becoming increasingly popular and are leading to dynamic river bed morphologies that in turn result in complex water level distributions in a river. Disconnected river branches, nonlinear longitudinal water level profiles and morphologically induced lateral water level gradients can evolve rapidly. The modeling of such river‐groundwater systems is of high practical relevance in order to assess the impact of restoration measures on the exchange flux between a river and groundwater or on the residence times between a river and a pumping well. However, the model input includes a proper definition of the river boundary condition, which requires a detailed spatial and temporal river water level distribution. In this study, we present two new methods to estimate river water level distributions that are based directly on measured data. Comparing generated time series of water levels with those obtained by a hydraulic model as a reference, the new methods proved to offer an accurate and faster alternative with a simpler implementation.  相似文献   

Soil organic carbon enrichment of dust emissions: magnitude,mechanisms and its implications for the carbon cycle     

Nicholas P. Webb  Craig L. Strong  Adrian Chappell  Samuel K. Marx  Grant H. McTainsh 《地球表面变化过程与地形》2013,38(14):1662-1671

Soil erosion is an important component of the global carbon cycle. However, little attention has been given to the role of aeolian processes in influencing soil organic carbon (SOC) flux and the release of greenhouse gasses, such as carbon dioxide (CO₂), to the atmosphere. Understanding the magnitude and mechanisms of SOC enrichment in dust emissions is necessary to evaluate the impact of wind erosion on the carbon cycle. This research examines the SOC content and enrichment of dust emissions measured using Big Spring Number Eight (BSNE) wind‐vane samplers across five land types in the rangelands of western Queensland, Australia. Our results show that sandy soils and finer particulate quartz‐rich soils are more efficient at SOC emission and have larger SOC dust enrichment than clay‐rich aggregated soils. The SOC enrichment ratios of dusts originating from sites with sand‐rich soil ranged from 2·1–41·9, while the mean enrichment ratio for dusts originating from the clay soil was 2·1. We hypothesize that stronger inter‐particle bonds and the low grain density of the aggregated clay soil explain its reduced capacity to release SOC during saltation, relative to the particulate sandy soils. We also show that size‐selective sorting of SOC during transport may lead to further enrichment of SOC dust emissions. Two dust samples from regional transport events were found to contain 15–20% SOC. These preliminary results provide impetus for additional research into dust SOC enrichment processes to elucidate the impact of wind erosion on SOC flux and reduce uncertainty about the role of soil erosion in the global carbon cycle. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献