IMPACT OF THE HEATINC OVER SOUTH ASIA UPON THE SUBTROPICAL HIGH OVER WEST-PACIFIC     

李双林  纪立人 《热带气象学报(英文版)》1999,5(2):141-152

A case is reported, during which the Subtropical High over the Western Pacific(hereafter, SHWP in abbreviation)shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments on SHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia will motivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day 3 result in the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP northward movement while the heating over ITCZ area tends to thvor SHWP westward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects after Day 5.  相似文献   

对区域数值模式(REM)的改进及数值试验     

周祖刚  张维桓  林乃实  孙明生 《热带气象学报》1999,15(2):146-153

针对中尺度对形对我国天气影响的重要性,对ＲＥＭ先后进行水平,垂直分辨率的提高,并运用常规报文资料获得初始场,运用包络地形方法获得模式所需的地形资料,对１９９４年７月１２－１３日的大暴雨个例进行了数值试验,结果表明,仅提高ＲＥＭ的水平分辨率,对降水预报有一定的改进和提高,但多报出了几个大暴雨中心。  相似文献   

Patterns and trends in nutrients and phytoplankton in Dutch coastal waters: comparison of time-series analysis, ecological model simulation, and mesocosm experiments   总被引：8，自引：0，他引：8  

de Vries  I.; Duin  R. N. M.; Peeters  J. C. H.; Los  F. J.; Bokhorst  M.; Laane  R. W. P. M. 《ICES Journal of Marine Science》1998,55(4):620-634

  相似文献   

Factors controlling the distribution of transitional metal elements in marine hydrogenic ferromanganese crusts     

JIANG Xuejun）  ）*  YAO De）  LIN Xuehui）    ZHAI Shikui）） College of Geoscience  Ocean University of China  Qingdao  P. R. China ） Qingdao Institute of Marine Geology  China Geological Survey  P. R. China ） College of Georesources  Environmental Engineering  Sh  ong University of Technology  Zibo  P. R. China 《中国海洋大学学报(英文版)》2009,8(1):57-64

A series of selective dissolution experiments were conducted on the hydrogenic ferromanganese crusts collected near Line Island to study the geochemistry of Mn, Fe, Cu, Co, Ni and Ti. Despite of the fact that the very close intergrowth between amorphous ferric oxyhydroxides and δ-MnO2 exists in the hydrogenic ferromanganese crusts, there is no isomorphous substitution between iron and manganese. This is because the two elements in oxides have different crystal chemistry and geochemistry, such assertion bein...  相似文献   

Erosion pattern of artificial gravel deposits   总被引：1，自引：1，他引：0  

Fabian Friedl  Volker Weitbrecht  Robert M. Boes 《国际泥沙研究》2018,33(1):57-67

Sediment replenishment with artificial gravel deposits is an option to compensate for sediment deficits in rivers and to improve their ecological conditions. Predicting and quantifying the erosion rate of an artificial gravel deposit is important to successfully perform river restoration projects. Laboratory experiments have been done to investigate the influence of various parameters on the erosion pattern of artificial gravel deposits. In the present paper the effects of deposit geometry, bulk density, grain size distribution, and hydraulic load on the erosion process are described. The temporal evolution of the deposit geometry and the corresponding mean erosion rates were studied. The mean erosion rate increases with deposit height, deposit width, and decreasing grain size. Furthermore, no significant impact of the bulk density was observed. Equations to predict the mean erosion rate are proposed. This investigation helps to determine the design frequency of gravel dumping and deposit volumes for restoration projects.  相似文献   

Bed roughness and grain sorting-an experimental study over fine to medium sand beds     

Barendra Purkait  Dipanjan Das Majumdar  Rajat Mazumder 《国际泥沙研究》2017,32(3)

The relation between grain-size distribution of the bed and in suspension was critically examined under a uniform flow velocity of 50 cm/s over two beds: one of mainly fine sands and the other of medium sands. Two sections – one 2.85 m downstream and the other 6.35 m downstream in the experimental channel-were selected for sampling to study the grain-sorting pattern in the vertical direction along the direction of transport. The shape and type of the grain-size distribution pattern were critically studied with height above the bed. The change in the distribution pattern has been attributed to the change of local bed roughness causing scouring against the protruded relatively coarse grains on the bed. Such trends are important to predict the nature of river bed topography. The sand of Bed-1 initially exhibits a log-skew-Laplace distribution at different heights of suspension. The distribution pattern, however, changes but this changing pattern is not consistent along the upstream side. For Bed-2, which initially exhibits a log-normal distribution, the same pattern persists from the height of suspension at 5 cm up to 20 cm. Such consistency in log-normality is also observed at the downstream points of measurement. It is generally expected that the mean grain-size would reduce with increases of suspension height but the results of the experiments, in some occasions, differ significantly from the gradual fining upward trend. This result has been attributed to local changes of bed roughness arising from the protruded relatively coarse grains causing eddies, scouring, and turbulent phenomena which moves coarse particles higher in suspension adding a coarse tail to the distribution increasing the mean grain-size.  相似文献   

Particle transport mechanics and induced seismic noise in steep flume experiments with accelerometer-embedded tracers     

Florent Gimbert  Brian M. Fuller  Michael P. Lamb  Victor C. Tsai  Joel P. L. Johnson 《地球表面变化过程与地形》2019,44(1):219-241

Recent advances in fluvial seismology have provided solid observational and theoretical evidence that near-river seismic ground motion may be used to monitor and quantify coarse sediment transport. However, inversions of sediment transport rates from seismic observations have not been fully tested against independent measurements, and thus have unknown but potentially large uncertainties. In the present study, we provide the first robust test of existing theory by conducting dedicated sediment transport experiments in a flume laboratory under fully turbulent and rough flow conditions. We monitor grain-scale physics with the use of ‘smart rocks’ that consist of accelerometers embedded into manufactured rocks, and we quantitatively link bedload mechanics and seismic observations under various prescribed flow and sediment transport conditions. From our grain-scale observations, we find that bedload grain hop times are widely distributed, with impacts being on average much more frequent than predicted by existing saltation models. Impact velocities are observed to be a linear function of average downstream cobble velocities, and both velocities show a bed-slope dependency that is not represented in existing saltation models. Incorporating these effects in an improved bedload-induced seismic noise model allows sediment flux to be inverted from seismic noise within a factor of two uncertainty. This result holds over nearly two orders of magnitude of prescribed sediment fluxes with different sediment sizes and channel-bed slopes, and particle–particle collisions observed at the highest investigated rates are found to have negligible effect on the generated seismic power. These results support the applicability of the seismic-inversion framework to mountain rivers, although further experiments remain to be conducted at sediment transport near transport capacity. © 2018 John Wiley & Sons, Ltd.  相似文献   

急陡沟道泥石流起动特征模型试验研究——以汶川县福堂沟为例   总被引：1，自引：0，他引：1  

李宁  唐川  龚凌枫  杨成长  陈明  甘伟 《地质学报》2020,94(2):634-647

急陡沟道泥石流是汶川震区发现的一类特殊泥石流,调查发现其具有物源量大、侵蚀强烈,冲出规模大等特点,是震区地质灾害治理的难点。本文以汶川县典型急陡沟道泥石流福堂沟为原型,分析了其发育条件和特征,并通过模型试验等手段,还原并分析了急陡沟道泥石流起动及形成的过程,以及相应的土体内部参数变化特征。试验显示在20°、25°、30°的坡度和480mL/s、410mL/s、360mL/s的径流量的试验条件下,泥石流分别以不同的方式起动(沟床侵蚀型、滑坡流态化起动型、消防管起动型),同时结合实验过程中土体内部孔隙水压力及体积含水率变化特征的研究,详细还原了相应的泥石流起动全过程。试验数据的分析结果显示,在不同的起动方式下,土体内部的数据变化表现出不同的特征:其中,不同试验条件下的泥石流起动孔隙水压力呈现出规律性差异,即水槽坡度、径流量越大,泥石流所需的起动力越小;此外,坡度越大,土体所需的饱水时间越长,而在相同坡度下,流速越大,预饱水时间越短;研究还发现,泥石流的爆发时间与沟床坡度呈反比,并且径流量越大,泥石流持续时间也越长。基于实验结果,通过相似理论计算得到的泥石流起动流速,与实际情况一致,表明本的研究结论可为汶川震区急陡沟道泥石流的研究提供参考。  相似文献   

The effect of flood intermittency on bifurcations in fluviodeltaic systems: Experiment and theory     

Max S. Daniller-Varghese  Wonsuck Kim  David C. Mohrig 《Sedimentology》2020,67(6):3055-3066

The dimensions and organization of deltaic islands and channels dictate delta morphology. This study presents experimental results modelling deposition at a river mouth and flow bifurcation around delta islands. Mouth bar formation and channel bifurcation is achieved in a laboratory setting by alternating input of suspended load transport and bedload transport. These two modes of transport produce two characteristic deposits with different advection lengths. Suspended load transport creates a steep deposit far from the inlet, while bedload creates a low angle, levéed deposit near the inlet. This study found that flow bifurcations occur where the proximal and distal deposits encroach on one another; and determined that there is a relationship between the frequency of suspended load transport and the length to channel bifurcation. Frequent flooding causes shorter length to bifurcations, whereas infrequent flooding causes greater length to bifurcations. This work overturns the hitherto understood mechanism of bifurcation location as a function of only high-transport conditions. Instead, the interactions between the sediment transport and deposition from normal flow and large-scale flooding events dictate delta island morphology.  相似文献   

湿地边界层通量影响热带气旋登陆维持和降水的数值试验   总被引：11，自引：3，他引：8  

李英  陈联寿 《气象学报》2005,63(5):683-693

用MM5v3模式及其TC Bogus方案对台风Nina(7503)在中国大陆上的维持加强过程进行模拟,并通过各种敏感性试验,研究了饱和湿地对热带气旋在大陆上维持和降水的影响。结果表明:湿地边界层内各通量对登陆热带气旋的强度、结构及其降水具有明显影响。潜热通量和感热通量均有利于热带气旋的维持和加强,其中潜热输送的作用显著,感热输送的作用较小。潜热和感热通量有利于热带气旋雨带螺旋结构的维持,对台风降水分布有明显影响,动量通量对热带气旋风场有显著的削弱作用,是其能量耗散、低压填塞的主要原因,但对台风降水具有局地增幅作用。  相似文献