Coherent eddies and temperature structure functions for three contrasting surfaces. Part I: Ramp model with finite microfront time     

Wenjun Chen  Michael D. Novak  T. Andrew Black  Xuhui Lee 《Boundary-Layer Meteorology》1997,84(1):99-124

Air temperature time series within and above canopies reveal ramp patternsassociated with coherent eddies that are responsible for most of thevertical transport of sensible heat. Van Atta used a simple step-changeramp model to analyse the coherent part of air temperature structurefunctions. However, his ocean data, and our own measurements for aDouglas-fir forest, straw mulch, and bare soil, reveal that even withoutlinearization his model cannot account for the observed decrease of thecubic structure function for small time lag. We found that a ramp model inwhich the rapid change at the end of the ramp occurs in a finite microfronttime can describe this decrease very well, and predict at least relativemagnitudes of microfront times between different surfaces. Averagerecurrence time for ramps, determined by analysis of the cubic structurefunction with the new ramp model, agreed well with values determined usingthe Mexican Hat wavelet transform, except at lower levels within theforest. Ramp frequency above the forest and mulch scaled very well withwind speed at the canopy top divided by canopy height. Within the forest,ramp frequency did not vary systematically with height. This is inaccordance with the idea that large-scale canopy turbulence is mostlygenerated by instability of the mean canopy wind profile, similar to aplane mixing layer. The straw mulch and bare soil experiments uniquelyextend measurements of temperature structure functions and ramp frequencyto the smallest scales possible in the field.  相似文献   

Distribution of Cs and Pu in the surface waters of the East Sea (Sea of Japan)     

Dong-Jin Kang  Chang Soo Chung  Suk Hyun Kim  Kyung-Ryul Kim  Gi Hoon Hong   《Marine pollution bulletin》1997,35(7-12):305-312

Surface and subsurface water samples for ¹³⁷Cs and ^239,240Pu analysis were collected in the East Sea (Sea of Japan) during August 1993. The ¹³⁷Cs levels of the surface waters are quite homogeneous in the East Sea (average = 3.1±0.2 mBq kg⁻¹). The ^239,240Pu levels vary from 6 to 10 μBq kg⁻¹ in the surface. ^239,240Pu to ¹³⁷Cs ratios in the surface water are within 0.002 to 0.003. The East Sea may be regarded as a part of the North Pacific Ocean in terms of ¹³⁷Cs dispersal in the surface, where the ¹³⁷Cs contents of the surface seawater seem to be controlled primarily by the atmospheric input. However, since our sampling was made just two months prior to the widely publicized Russian dumping incident on the 17th October 1993, our measurements may provide background data to assess the immediate impact of the Russian dumping on the levels of ¹³⁷Cs and ^239,240Pu in the East Sea.  相似文献   

Lubbock Lake: Late Quaternary studies on the Southern High Plains : Edited by Eileen Johnson. Texas A&M Univ. Press, College Station, 1987, 179pp., tables, illustrations, $49.50     

Lee Ann Kreutzer 《Quaternary Research》1988,30(3)

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Three-dimensional diffraction of elastic waves by a spherical cavity in an elastic half-space, I: Closed-form solutions     

Vincent W. Lee 《Soil Dynamics and Earthquake Engineering》1988,7(3)

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On the speciation of metals in the water column of a polluted estuary     

George W. Luther III  Zbigniew Wilk  Robert A. Ryans  A. Lee Meyerson 《Marine pollution bulletin》1986,17(12):535-542

The dissolved (<0.40 γm) fraction of water samples from Newark Bay, New Jersey was analysed for Zn, Cu and Pb content by differential pulse anodic stripping polarographic techniques. In the dissolved fraction, non-labile forms of Zn, Cu and Pb exist as shown by differential pulse anodic stripping voltammetry analysis on acidified samples and acidified-UV irradiated samples. The particulate fraction (>;0.40 μm) contains metals in the form of sulphides (Fe, Zn, Cu, Mn), oxides and oxyhydroxides (Si, Al, Fe, Cu, Ni, Sn), phosphate (Ca, Ce, La), clay minerals (Fe, Zn, Cu, Ti) and carbonaceous material (Fe, Cu, Zn) as demonstrated by X-ray microanalysis. The solid phases are likely present in colloidal form in the dissolved fraction of the water column as well. The forms of the metals in the water column are partially due to the resuspension of bottom sediments by dredging and natural processes, to sewage outfall and to natural geochemical processes.  相似文献   

The intermittent vertical heat flux over a spruce forest canopy     

Richard H. Grant  Gary E. Bertolin  Lee P. Herrington 《Boundary-Layer Meteorology》1986,35(4):317-330

Vertical heat and momentum fluxes were measured by the eddy correlation method under near-neutral conditions during both day and night above a spruce forest canopy. Results show that 50% of the heat transported to the spruce canopy during night and away from the canopy during the day occurs in extreme magnitude events, the majority of less than one second duration. Extreme-magnitude events were more frequent and lasted longer during the day than during the night. The distributions of the duration of extreme events in the same direction as the net heat flux and the turbulence intensity for both day and night were similar.During the night, the mean horizontal windspeed was about 1 m s^-1 and the measured coincident transport of momentum and heat accounted for 36% of the total heat flux. The predominant mechanism of forced convection during the extreme nightime heat transport events was excess heat sweeps in which the duration of the event is usually less than 1 s. During the day, the mean horizontal windspeed was about 2 m s ^-1 and the measured coincident transport of momentum and heat accounted for only 16% of the total heat flux. Local free convection was suggested to account for 27% of the total heat flux. The predominant mechanism of mixed convection during the extreme daytime heat transport events is deficit heat inward interactions. During both night and day, about 10% of the total heat transport occurred in extreme events working against the thermal gradient.Now atPurdue University, West Lafayette, IN, U.S.A.  相似文献   

Occurrence,chemistry, and origin of immiscible silicate glasses in a tholeiitic basalt: A TEM/AEM study     

Lung -Chuan Kuo  Jung H. Lee  Eric J. Essene  Donald R. Peacor 《Contributions to Mineralogy and Petrology》1986,94(1):90-98

The occurrence and chemistry of immiscible silicate glasses in a tholeiite mesostasis from the Umtanum formation, Washington, were investigated with transmission electron microscopy and analytical electron microscopy (TEM/AEM). TEM observation reveals isolated, dark globules (2.1 micron or less in diameter) randomly distributed in a transparent matrix glass interstitial to plagioclase laths. The globules less than 0.3 micron and larger than 0.8 micron fall beyond the linear relationship defined by the 0.3–0.8 micron globules in a plot of the logarithm of number versus size. Large globules (0.7 micron or larger in diameter) range from homogeneous to heterogeneous in optical properties and chemistry. Homogeneous globules are completely glassy, whereas heterogeneous globules contain crystalline domains. AEM analyses show that the globules have high Si, Fe, Ca, and Ti with subordinate Mg, Al, P, S, Cl, K, and Mn, which gives high normative fa, px, il, and ap. The matrix glass consists dominantly of Si with low Al and minor Na and K, yielding a high normative qz, or, ab, and an.It is proposed that the silicate liquid immiscibility occurs by reaction of network-modifying cations (NMCs) with dominantly chain-like anionic units in the parental melt to form less polymerized, NMC-bearing units and highly polymerized, Si-rich units. The globules nucleated metastably under supercooled conditions, and medium-size globules become either larger or smaller at lower temperatures. Internal nucleation of NMC-rich phases occurred in some larger globules upon cooling.  相似文献   

Phytoplankton dynamics within Gulf Stream intrusions on the southeastern United States continental shelf during summer 1981     

James A. Yoder  Larry P. Atkinson  S. Stephen Bishop  Jackson O. Blanton  Thomas N. Lee  Leonard J. Pietrafesa 《Continental Shelf Research》1985,4(6):611-635

During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 10¹ km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area.Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m⁻ d⁻¹ and 75 mg m⁻, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO₃-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a⁻¹ h⁻¹), high mean α (14 mg C mg Chl a⁻¹ Ein⁻¹ m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters.The results imply a seasonal (June to August) middle shelf production of 150 g C m⁻¹, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area.  相似文献   

Isolation of diagenetic overgrowths on quartz sand grains for oxygen isotopic analysis     

Mingchou Lee  Samuel M. Savin 《Geochimica et cosmochimica acta》1985,49(2):497-501

Diagenetic overgrowths on detrital quartz sand grains in sandstones can be isolated for direct measurement of their oxygen isotope ratios. Interfacial materials between detrital cores and diagenetic overgrowths are dissolved by etching with dilute HF. The weakened interface breaks when grains are agitated ultrasonically. Subsequent particle size separation is an effective means of concentrating the diagenetic component.  相似文献   

Dynamic response of twin circular tunnels due to incident SH-waves     

Thambirajah Balendra  David P. Thambiratnam  Chan Ghee Koh  Seng-Lip Lee 《地震工程与结构动力学》1984,12(2):181-201

The steady-state solution for two parallel under ground tunnels of circular cross-section subjected to incident plane harmonic SH-waves is obtained in closed form, by using the method of wave function expansion. The image technique is employed to account for the reflection of waves at the ground surface. Numerical studies are carried out to determine the influence of spacing between the tunnels on the shear stresses in concrete and steel linings.  相似文献