Numerical studies on typhoon surges in the Northern Taiwan     

Wei-Po Huang  Chiang-An Hsu  Chen-Shan Kung  John Z. Yim 《Coastal Engineering》2007,54(12):883-894

A numerical model for the simulation of typhoon surge has been developed for the coastal areas of the northern Taiwan. Results from the model outputs are then used as a typhoon surge data bank for 7 main estuary areas in this region. The data bank consists of the historical typhoon events from 1980 to 2004. Both characteristic and frequency analyses of the typhoon surge in the coastal region have been studied. Using these data, a relation between the surge height and pressure distribution is obtained. It is shown that, either the numerical model, or the statistical equations presented in this paper, can be used to predict possible surge heights in the estuary areas with sufficient accuracy.  相似文献   

Boron isotopic fractionation during seawater evaporation   总被引：6，自引：0，他引：6  

Y.K. Xiao  S.Z. Li  H.Z. Wei  A.D. Sun  W.G. Liu  W.J. Zhou  Z.Q. Zhao  C.Q. Liu  G.H. Swihart 《Marine Chemistry》2007,103(3-4):382-392

Laboratory experiments were undertaken to investigate the behaviour of boron at the seawater–air interface during seawater evaporation. Seawaters adjusted to different pH values were heated to 27, 33 and 40 °C inside a quartz evaporator. The vapor was collected with a quartz condenser using a cold trap. A natural seawater–vapor process in quiet air conditions and excluding the sea-spray component was realized using this arrangement. The results indicate an enrichment of ¹¹B in the condensate. This implies that in the natural environment, rainfall with δ¹¹B values lower than that of seawater has been affected either by continental boron sources or by the boron extracted from seawater under airflow conditions. While the net flux of boron carried away from the ocean by air masses due to seawater evaporation is significant compared to other fractionation-associated processes removing boron from the ocean, the effect of isotopic fractionation as boron enters the vapor phase on the isotopic composition of boron in the ocean over time is small.  相似文献   

Convection zone of white-dwarf stars     

Z. M. Atweh  D. Eryurt-Ezer 《Astrophysics and Space Science》1992,187(1):27-36

The boundary convection zones of hot helium white-dwarf stars (WDSs) in the range 17000 KT _e30000 K are studied. Recently, an anisotropic mixing-length theory (AMLT) which determines the mixing-length parameter locally is applied for the convection zones calculation. Comparing with the calculations by using the (MLT), it is found that maximum velocity decreases appreciably, and the other boundary conditions are affected.  相似文献   

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors     

McDonnell JA  Alexander WM  Burton WM  Bussoletti E  Evans GC  Evans ST  Firth JG  Grard RJ  Green SF  Grun E  Hanner MS  Hughes DW  Igenbergs E  Kissel J  Kuczera H  Lindblad BA  Langevin Y  Mandeville JC  Nappo S  Pankiewicz GS  Perry CH  Schwehm GH  Sekanina Z  Stevenson TJ  Zarnecki JC et AL 《Astronomy and Astrophysics》1987,187(1-2):719-741

Analysis of the data from Giotto's Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (>10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.  相似文献   

Meterwave observations of a coronal hole     

Z. Wang  E. J. Schmahl  M. R. Kundu 《Solar physics》1987,111(2):419-428

We present meterwave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in He i l10830 spectroheliograms.Using the model of coronal holes by Dulk et al. (1977) we derive the electron density from the radio observations of the brightness temperature. The discrepancy between the density value derived from the Skylab EUV data and that computed from our radio data is even larger than in Dulk et al. 's comparison at similar and higher frequencies.  相似文献   

Spectral analysis and the two-dimensional distribution of physical parameters in a quiescent prominence     

Q. Z. Zhang  W. C. Livingston  J. Hu  C. Fang 《Solar physics》1987,114(2):245-252

The profiles of H and Ca ii K lines of a arch quiescent prominence on April 1, 1971 have been analyzed and the two-dimensional distributions of electron temperature T _e , micro-turbulence velocity v _t and the column number density of hydrogen along the line-of-sight N _H have been obtained. T _e , _t , and N _H are found to be 7500 K, 6 km s^–1 and 2.2 ^× 10¹⁸ cm^–2 on an average, respectively. The electron temperature at the central part of the prominence and along the two arcades are greater than that at the edges, while the distribution of the micro-turbulence velocity in these regions is opposite. There is no systematic variation in T _e and v _t , from the center to the periphery as described by Hirayama (1971). The column number density in the central region is lower than that at the two edges.The contour lines of T _e , _t , and N _H are predominantly vertical rather than horizontal. This implies that the height-variation of physical parameters in filamentary structure is small. The arrangement of this structure in the prominence is likely to be arched and is probably in the direction of magnetic field lines.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

A new potential function for the calculation of contact forces in the combined finite–discrete element method          下载免费PDF全文

C.Z. Yan  H. Zheng 《国际地质力学数值与分析法杂志》2017,41(2):265-283

Although the potential contact force proposed by Munjiza overcomes the difficulties inherent in the traditional discrete element methods, the physical meaning of the potential is not clear and the contact force derived from the original potential function is strongly dependent on the mesh configuration. In this study, we redefine a potential function and propose a new contact force calculation method based on a unified standard. Moreover, the new potential function retains all the advantages of the original potential function but has less mesh dependency. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Résumé of research into river channel changes conducted in the USSR / Résumé des recherches des changements des lits des rivières effectuées dans l'URSS     

V. V. KUPRIANOV  Z. D. KOPALIANI 《水文科学杂志》2013,58(3):345-349

Abstract

This paper describes briefly some findings and investigations on the problem of channel processes conducted in the USSR. It was stimulated by the publication of River Channel Changes (Gregory, 1977).  相似文献   

Sensitivity of evapotranspiration and soil moisture in wheat fields to changes in climate and direct effects of carbon dioxide     

L. S. KUCHMENT  Z. P. STARTSEVA 《水文科学杂志》2013,58(6):631-643

Abstract

A physically based model of moisture transfer in the soil-canopy-atmosphere system, fitted to measured data in wheat fields, was applied to calculate the sensitivity of evapotranspiration to the combined effect of possible CO₂-induced climate changes and the direct impact of doubling CO₂ content in the atmosphere. The impact of carbon dioxide was taken into account by changing the stomatal resistance and the leaf area index. Several climate change scenarios were used. Simulation studies showed that when the changes of a number of climatic and plant factors are considered, evapotranspiration responses can differ greatly from those that consider only temperature change. The temperature effect of the increase in CO₂ content in the atmosphere can be compensated by changes in the physiological parameters of vegetation. Thus, under certain conditions, one can expect a decrease in evapotranspiration instead of an increase such as is predicted by a number of models which neglect the direct effects of CO₂ on plant behaviour.  相似文献   

Hydrologic impact of regional climate change for the snowfed and glacierfed river basins in the Republic of Tajikistan: hydrological response of flow to climate change     

S. Kure  S. Jang  N. Ohara  M. L. Kavvas  Z. Q. Chen 《水文研究》2013,27(26):4057-4070

The warming of the Earth's atmosphere system is likely to change temperature and precipitation, which may affect the climate, hydrology and water resources at the river basins over the world. The importance of temperature change becomes even greater in snow or glacier dominated basins where it controls the snowmelt processes during the late‐winter, spring and summer months. In this study hydrologic responses of streamflow in the Pyanj and Vaksh River basins to climate change are analysed with a watershed hydrology model, based on the downscaled atmospheric data as input, in order to assess the regional climate change impact for the snowfed and glacierfed river basins in the Republic of Tajikistan. As a result of this analysis, it was found that the annual mean river discharge is increasing in the future at snow and glacier dominated areas due to the air temperature increase and the consequent increase in snow/ice melt rates until about 2060. Then the annual mean flow discharge starts to decrease from about 2080 onward because the small glaciers start to disappear in the glacier areas. It was also found that there is a gradual change in the hydrologic flow regime throughout a year, with the high flows occuring earlier in the hydrologic year, due to the warmer climate in the future. Furthermore, significant increases in annual maximum daily flows, including the 100‐year return period flows, at the Pyanj and Vaksh River basins toward the end of the 21st century can be inferred from flood frequency analysis results. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献