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51.
为了探索宽窄相间河道的水流紊动特性,以西南地区宝兴河上游宽窄相间河段为研究对象,基于室内概化模型试验,采用多普勒声学流速仪(ADV)测量了室内模型典型断面上的三维瞬时流速,分析典型断面上的纵向时均流速、紊动强度、雷诺切应力和紊动能的分布规律。试验结果显示:宽窄相间水槽中,扩散段边壁的紊动强度大于中心区域的紊动强度,最大值位于0.2倍水深处;扩散段两侧坡脚处紊动能最大;侧壁区的平面和立面雷诺切应力最大值出现在扩散段内,中心区域最大雷诺切应力位于两槽间的中间断面处;扩散段内水流紊乱,两侧出现旋涡和涡脱,易造成侧壁侵蚀加强,引起河道拓宽。深入分析了宽窄相间河道水流的紊动特性,可为山区河流治理和自然灾害防治提供参考。 相似文献
52.
Falling sphere observations of anisotropic gravity wave motions in the upper stratosphere over Australia 总被引:1,自引:0,他引:1
A study of inertial scale gravity wave motions in the region of the atmosphere between 30 and 60 km has been undertaken, using wind and temperature data derived from rocket-borne falling sphere density experiments performed over Woomera, Australia between 1962 nad 1976. The gross features of the wave field compare favorably with those found in similar northern hemispheric studies. Wave propagation is found to be both vertically and horizontally anisotropic. A rotary spectral analysis indicates predominately upgoing wave energy, suggesting that the majority of sources of these waves lie below 30 km. A detailed statistical investigation of the waves, made using the Stokes parameters technique, reveals that phase progression is also highly directional in the horizontal, with a significant zonal component in summer, but with a strong meridional component in winter. Propagation towards the southeast is inferred in summer, with the waves possibly emanating from tropospheric sources in equatorial regions to the north of Australia. The technique also shows that, on average, the waves appear to have mean ellipse eccentricities (=f/) around 0.4–0.45. Indirect estimates of a number of important wave parameters are made. In particular,v andw flux estimates are made over several height intervals. The vertical gradient of density weighted flux implies wave-induced mean flow accelerations of the order 0.1–1 ms–1day–1. This suggests that dissipating gravity waves are a significant source of the momentum residuals that are encountered in studies of satellite data from this region. 相似文献
53.
Transient and stationary spectra of kinetic energy (KE), available potential energy (APE) and enstrophy (EN), and their spectral fluxes as a function of the two-dimensional wavenumbern were computed for July 1979. Triangular truncation at zonal wavenumber 42 was used for computation. The slopes of various
spectra in the wavenumber range 14≤n≤25 were obtained by fitting a straight line in log-log scale by the least square method. The transientKE, APE andEN spectra in the lower (upper) troposphere had slopes −2·21 (−2·30), −2·65 (−2·64) and −0·36 (−0·46), respectively. The effect
of stationary and divergent motion on the slope values was investigated. The possible correlation between the slope and percentage
of transient component in the combined energy and enstrophy was examined to identify the transient motion of the atmosphere
with the two-dimensional homogeneous isotropic turbulence. The vertically averaged slope of kinetic energy and enstrophy in
the lower (upper) troposphere was close to the value at 700 (200) hPa level.
The spectral fluxes of kinetic energy and enstrophy in the wavenumber range 14≤n≤25 satisfied, to a very rough approximation, the criteria of inertial subrange. The stationary fluxes were small. The estimated
stationary-transient component of flux was larger, comparable and less than the corresponding transient flux of APE, KE and
EN.
Representative levels for computation of energy and enstrophy spectra and their fluxes in the lower and upper troposphere
were identified. 相似文献
54.
Radiometric dating of lake sediments from Signy Island (maritime Antarctic): evidence of recent climatic change 总被引:4,自引:0,他引:4
Sediment cores from three lakes (Moss, Sombre and Heywood) in the maritime Antarctic (Signy Island, South Orkney Islands) have been successfully dated radiometrically by210Pb and137Cs. The core inventories of both fallout radionuclides are an order of magnitude higher than that which can be supported by the direct atmospheric flux at this latitude. The elevated values may be explained by fallout onto the catchment during the winter being delivered directly to the lakes during the annual thaw. Two of the lakes (Sombre and Heywood) show marked increases in sediment accumulation afterc. 1950. This appears to be associated with a documented rise in temperature in the South Orkney Islands, which has caused extensive deglaciation at Signy Island.This is the tenth of a series of papers to be published by this journal following the 20
th
anniversary of the first application of210Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series. 相似文献
55.
Emission of nitric oxide from soils and termite nests in a Trachypogon savanna of the Orinoco basin 总被引:2,自引:0,他引:2
Alberto Rondón Christer Johansson Fugenio Sanhueza 《Journal of Atmospheric Chemistry》1993,17(3):293-306
Nitric oxide fluxes from soils in the Trachypogon savanna of the Orinoco basin were determined during the dry season using the static chamber method. The emission from dry soils fluctuated from 0.4 to 3 ng N m–2 s–1 and increased up to 25 ng N m–2 s–1 after moderate watering or light rain-falls (1 to 5 mm). The mean emission values are up to 6 times lower than one observed earlier at the Chaguaramas site, but up to 10 times higher than one recorded at the Guri site, indicating an important spatial variability in NO fluxes of the Venezuelan savanna region. The changes observed after the addition of nitrogen to the soil, in the form of ammonium and/or nitrate, indicate a high denitrification potential in this acidic soil. Burning of the surface vegetation produced an increase by a factor of 10 in the emission rate of NO, but the effect was relatively short in time, about 5 days. It was estimated for the savanna region that burning increases the total NO soil emission during the dry season by 15% compared to the unburnt case. Soils with termite nests emit 10 times more NO than soil without nests, but the contribution from this source is less than 2% of the total savanna soil flux. 相似文献
56.
57.
本文根据核爆炸岩石熔融玻璃的地球化学研究结果,与超速陨石撞击坑的熔岩进行比较,获得在远离热力学平衡条件下,各种玻璃和熔岩在化学成分上分布十分均匀的重要结论。岩石玻璃和熔岩是由基岩各组成岩石按一定比例混合熔融形成的。它们的主量元素和痕量元素丰度受基岩元素背景值制约。文中根据熔体和靶岩的化学成分,计算了熔岩各组成岩石的百分比。玻璃陨石是地壳岩石受撞击熔融形成的。同一撒布区的玻璃陨石化学成分相近,说明起源于同一源坑;而玻璃陨石化学成分的不同,则说明母岩组成分量的差异。因此,文中通过模拟计算,得出各玻璃陨石的组成源岩。澳大利亚撒布区的玻璃陨石,Al2O3,K2O 和Na2O 与 SiO2及 K2O/Na2O 比值不完全相同,说明澳大利亚撒布区存在着几个不同的源岩和源坑,至少有印支、爪哇、菲律宾和澳大利亚四个相应撞击坑。 相似文献
58.
Stefan Keller 《Surveys in Geophysics》1995,16(5-6):661-670
Laboratory simulation of powder snow avalanches serves for the validation of numerical models and as a tool in its own right for consulting and research purposes. Two-phase gravity currents are simulated in water with quartz powder or glass spheres as the particle phase. Particle-phase velocity profiles and particle-phase volume fraction profiles are measured with an ultrasonic device. The experimental setup and the current state of the measurement technique are described and preliminary results are presented. 相似文献
59.
Ismail Gultepe 《Pure and Applied Geophysics》1995,144(2):321-350
Observations taken by aircraft and conventional platforms are used to investigate dynamical, physical, and radiative processes within a marine stratus cloud during the Canadian Atlantic Storms Program (CASP) II field project which took place over the east coast of Canada. Stratus which formed over the ocean on February 6, 1992 during the nighttime, is studied to analyze cloud top and base processes. The cloud was supercooled during the study period. Fluctuations and fluxes are calculated along constant flight altitude legs approximately 100 km long in space. The scales of structures larger than 5 km are removed from the analysis using a running average technique. Droplet spectra obtained by a forward scattering spectrometer probe (FSSP) were used in a 1-D radiative transfer model to calculate infrared (IR) fluxes and radiative heating rates. A heat conservation equation was used to estimate vertical air velocity (w
a
) within the cloud. The results showed that, because of a warmer ocean surface, significant moisture and heat were transferred from the ocean surface to the boundary layer. The cloud base was at about 400 m height and the top was at about 1.4 km.w
a
at the cloud base was estimated about 5 cm s–1. Strong IR cooling rate at the cloud top was calculated to be 75°C day–1 for a 100 m thick layer. Negative skewness inw
a
, suggesting narrow downdrafts, was likely due to radiative cooling at the cloud top. The entrainment velocity was found to be about 1.5 cm s–1 at cloud top. Mean moisture and heat fluxes within the cloud were estimated to be comparable to those from the ocean surface. Vertical air velocity at the cloud top due to radiative cooling was found to be about –40 cm s–1. 相似文献
60.
The paper describes a stationary model of the boundary layer of a large-scale vortex. The model takes into account two types of nonlinearities: (1) advection of the momentum and centrifugal accelerations, that is related to large values of the Rossby number; (2) a nonlinear turbulent friction on the lower boundary (generally speaking, not only quadratic, but also more complicated). Nevertheless, the model may be studied analytically. This approach allows discovery and analysis of several universal regularities, which are not revealed by numerical modeling. The model provides the actual values for the speed of the surface wind and the angle of cross-isobar surface flow in the tropical cyclones. 相似文献