Moderately stable flow over a three-dimensional hill A comparison of linear theory with laboratory measurements     

ROGER S. THOMPSON  MICHAEL S. SHIPMAN  JAMES W. ROTTMAN 《地球，A辑:动力气象学与海洋学》1991,43(1):49-63

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Annual variation of the global precipitable water and its maintenance: observation and climate-simulation     

TSING-CHENG CHEN  MING-CHANG YEN  JAMES PFAENDTNER  Y. C. SUD 《地球，A辑:动力气象学与海洋学》1996,48(1):1-16

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Age determination of intermoraine areas, Austerdalen, southern Norway     

JUDITH K. MAIZELS  JAMES R. PETCH 《Boreas: An International Journal of Quaternary Research》1985,14(1):51-65

This paper is concerned with the size variation of thalli of the lichen Rhizocarpon geographicum agg. on intermoraine surfaces in the proglacial valley of Austerdalen, southern Norway, and with the use of thallus dimensions for both relative and absolute dating of intermoraine deposits. Measurements of the five largest lichens in 200 m² search areas at 255 sites show significant cross-valley and down-valley variations, with the smallest thalli located towards the centre of the valley and at up-valley sites. This variation has been examined in greater detail by dividing the intermoraine areas into twelve morphological zones, for which geomorphological and stratigraphical relations enable the construction of a relative time sequence of formation. This relative time sequence was then found to he confirmed by mean values of measurements of the largest lichen thalli in 100 m square quadrats within each morphological zone. This approach has allowed not only the relative age of morainic and intermorainic deposits to he established from geomorphological evidence but also, using tentative dates for the moraines, the construction of a chronology of moraine and intermoraine depositional events.  相似文献   

Relation of atmospheric CO₂ to tropical sea and air temperatures and precipitation     

WILLIAM P. ELLIOTT  JAMES K. ANGELL  KIRK W. THONING 《Tellus. Series B, Chemical and physical meteorology》1991,43(2):144-155

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A Study on Retrieving Atmospheric Profiles from EOS/AIRS Observations   总被引：5，自引：0，他引：5  

GUAN Li  ALLEN Huang  LI Jun 《Acta Meteorologica Sinica》2005,19(1):112-119

1. IntroductionThe development of global climate and weathermodels requires accurate monitoring of atmospherictemperature and moisture profiles, as well as the con-tents of trace gases and aerosols. It is quite difficultto monitor continuously these parameters on a globalscale.Until recently. AIRS (Atmospheric InfraredSounder) offers a new opportunity to improve globalmonitoring of temperature, moisture, and ozone distri-butions and changes therein. The high spectral resolu-tion (v/Δv ? 12…  相似文献   

The orientation of helical flow in curved channels     

RANSOME K. T. CORNEY†  JEFFREY PEAKALL  DANIEL R. PARSONS  LIONEL ELLIOTT†  KATHRYN J. AMOS  JAMES L. BEST  GARETH M. KEEVIL  DEREK B. INGHAM† 《Sedimentology》2006,53(2):249-257

The planform patterns of meandering submarine channels and subaerial fluvial bends show many similarities that have given rise to strong analogies concerning the fluid dynamics of these channel types. Existing models of helical motion in open‐channel bends depict flow that is characterized by surface flow towards the outer bank, and basal flow towards the inner bank. This paper investigates and compares, through an analytical model and physical experiment, flows within fluvial meanders, and submarine channel bends that contain density‐driven gravity currents. The results indicate that the sense of helical motion can be reversed in submarine bends that contain density currents when compared with fluvial bends, and that the orientation of the helical flow is dependent on the vertical distribution of downstream velocity. Specifically, the sense of helical motion is reversed in bends when the maximum downstream velocity is near the bed, resulting in near‐bed flow towards the outer bank. These findings suggest that the dynamics of sediment transport and deposition in curved channels with such velocity profiles will be fundamentally different to those currently assumed from sinuous open‐channels.  相似文献   

Resedimentation of cold pumiceous ignimbrite into water: facies transformations simulated in flume experiments     

S. R. ALLEN  A. FREUNDT† 《Sedimentology》2006,53(4):717-734

Deposits and transport processes resulting from the resedimentation of cold, unconsolidated ignimbrite into water were simulated by flume experiments. The ignimbrite sample used was poorly sorted (σ = 2·4–3), fine ash‐rich (< 63 μm, 17–30 wt%) and included both dense lithic clasts (> 2000 kg m^?3) and pumice (500 to ca 1300 kg m^?3). As a result of the binding forces of the ash matrix, the experiments involved resedimentation from a steep front onto the floor (with or without an initial ramp) of the water‐filled tank under both still and wave‐generated conditions. Larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action. The mass of the collapse and proportion of pore–space water strongly influenced the style of resedimentation and the deposits. Initial collapse events were from the top of the steep front and fell onto the floor. The largest, densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break‐in‐slope. Fine ash was transported in dilute turbidity currents, and coarse unsaturated pumice clasts floated off. Moderate collapse events generated high‐density turbidity currents, trapping pumice in the flow, causing them to saturate. These low‐density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit. Large collapse events slumped, producing poorly sorted mounds similar in texture to the original starting material. As the matrix of the ignimbrite sample became saturated with water, moderate and large collapse events generated debrisflows and slurries that deposited massive, poorly sorted deposits. Furthermore, once more gentle slopes were established between the sample and deposit, small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low‐relief, ash channels. The experiments show that, excluding large collapse events and debrisflows, resedimenting ignimbrite in water is effective at segregating low‐density pumice clasts from dense lithic clasts and fine ash. Experiments using fine‐ash poor ignimbrite and well‐sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches. The grainflow deposits had textures similar to the fines‐poor starting material.  相似文献   

Water quality management: general     

JAMES KEMPF 《水文科学杂志》2013,58(2):167-170

Abstract

Rainfall is the main source of irrigation water in the northeastern part of Thailand where the inhabitants derive their income primarily from farming. In order to improve their economic conditions, the efficient use of available water is essential and this requires a sound understanding of the distribution of rainfall in space and in time. The present study aims at providing basic information on rainfall sequences in the region, such as their amount and their distribution in space and time. Several other statistical properties such as the persistence, the periodicity and the degree of irregularity of rainfall and the transition probabilities between rainy and non-rainy days are presented. An assessment of the availability of water for irrigation is also made.  相似文献   

The Plagioclase-Magma Density Paradox Re-examined and the Crystallization of Proterozoic Anorthosites   总被引：4，自引：1，他引：3  

SCOATES  JAMES S. 《Journal of Petrology》2000,41(5):627-649

Intermediate-composition plagioclase (An_40–60) is typicallyless dense than the relatively evolved basaltic magmas fromwhich it crystallizes and the crystallization of plagioclaseproduces a dense residual liquid, thus plagioclase should havea tendency to float in these magmatic systems. There is, however,little direct evidence for plagioclase flotation cumulates eitherin layered intrusions or in Proterozoic anorthosite complexes.The layered series of the Poe Mountain anorthosite, southeastWyoming, contains numerous anorthosite–leucogabbro blocksthat constrain density relations during differentiation. Allblocks are more mafic than their hosting anorthositic cumulates,their plagioclase compositions are more calcic, and each blockis in strong Sr isotopic disequilibrium with its host cumulate.Associated structures—disrupted and deformed layering—indicatethat (1) a floor was present during crystallization and thatplagioclase was accumulating and/or crystallizing on the floor,(2) compositional layering and plagioclase lamination formeddirectly at the magma–crystal pile interface, and (3)the upper portions of the crystal pile contained significantamounts of interstitial melt. Liquid densities are calculatedfor proposed high-Al olivine gabbroic parental magmas and Fe-enrichedferrodioritic and monzodioritic residual magmas of the anorthositestaking into account pressure, oxygen fugacity, P₂O₅, estimatedvolatile contents, and variable temperatures of crystallization.For all reasonable conditions, calculated block densities aregreater than those of the associated melt. The liquid densities,however, are greater than those for An_40–60 plagioclase,which cannot have settled to the floor. Plagioclase must eitherhave been carried to the floor in relatively dense packets ofcooled liquid plus crystals or have crystallized in situ. Asloping floor, possibly produced by diapiric ascent of relativelylight plagioclase-rich cumulates, is required to allow for drainingand removal of the dense interstitial liquid produced in thecrystal pile and may be a characteristic feature during thecrystallization of many Proterozoic anorthosites and layeredintrusions. KEY WORDS: magma; density; Proterozoic anorthosites; blocks; plagioclase  相似文献   

ENVIRONMENTALISM AND EUROCENTRISM     

JAMES M. BLAUT 《Geographical review》1999,89(3):391-408

ABSTRACT. Environmental determinism has served to validate a Eurocentric world history for several centuries, and it continues to do so today. This essay looks briefly at the historical marriage between environmental determinism and Eurocentric history, then develops a detailed critique of the environmental determinism put forward in two recent world-history books: Jared Diamond's Guns, Germs, and Steel (1997) and David Landes's The Wealth and Poverty of Nations (1998).  相似文献