北部湾潮汐的伴随同化数值模拟

影响潮汐和潮流模拟精度的两个主要因素是对开边界条件和底摩擦系数的选取。如果能给出优化的开边界条件和底系数摩系数,则必将提高潮汐和潮流模拟的精度。     

Form Drag Caused by Topographically Forced Waves in a Barotropic β Channel: Effect of Higher Mode Resonance

The relationship between form drag and the zonal mean velocity of steady states is investigated in a very simple system; a barotropic quasi-geostrophic β channel with sinusoidal topography. When a steady solution is calculated by the modified Marquardt method, keeping the zonal mean velocity constant as a parameter, the characteristic of the solution changes at a phase speed of a wave with a wavenumber higher than that of the bottom topography. For velocities smaller than this critical value, there exists a stable quasi-linear solution similar to the linear solution. For larger velocities, there exist three solutions whose form drag is very large. In addition, the resonant velocity of the mode, whose wavenumber is the same as the bottom topography, has no effect on these solutions. When the quiescent fluid is accelerated by a constant wind stress, acceleration stops around the critical velocity for a wide range of the wind stress. If the wind stress is too large for the acceleration to stop, the zonal current speed continues to increase infinitely. It is implied that the zonal velocity of equilibrium is mainly determined, not by the wind stress, but by the amplitude of the bottom topography and the viscosity coefficient.     

Sponges from Trawl-Exploitable Bottoms of Ligurian and Tyrrhenian Seas: Distribution and Ecology*

Abstract. Sponges from muddy and dctritic bottoms along the coasts of Liguria and Tuscany (Western Méditerranean) were studied to 700 m depth. The distribution of the 66 species identified was compared with depth, geographic location, as well as type of bottom and benthic community in order to determine whether a typical sponge fauna exists in these environments. The most common species (Suberites carnosus, S.ficus, Thenea muricata) are characteristic soft bottom dwellers, but the remaining sponge fauna seems to be linked to the presence of small patches of hard substrate scattered on these bottoms. As a consequence, the neighbouring hard bottom biocoenoses may remarkably affect the composition of this fauna by an export of larvae. Many species are clearly eurybathic, but most were recorded between 50 and 200 m. Type and size of the available substrate for sponge settlement and growth are apparently the most important Écological factors affecting the studied fauna.     

Precise Positioning of Ocean Bottom Seismometer by Using Acoustic Transponder and CTD

We have obtained precise estimates of the position of Ocean Bottom Seismometers (OBS) on the sea bottom. Such estimates are usually uncertain due to their free falling deployment. This uncertainty is small enough, or is correctable, with OBS spacing of more than 10 km usually employed in crustal studies. But, for example, if the spacing is only 200 m for OBS reflection studies, estimates of the position with an accuracy of the order of 10 m or more is required.The determination was carried out with the slant range data, ship position data and a 1D acoustic velocity structure calculated from Conductivity–Temperature–Depth (CTD) data, if they are available. The slant range data were obtained by an acoustic transponder system designed for the sinker releasing of the OBS or travel time data of direct water wave arrivals by airgun shooting. The ship position data was obtained by a single GPS or DGPS. The method of calculation was similar to those used for earthquake hypocenter determination.The results indicate that the accuracy of determined OBS positions is enough for present OBS experiments, which becomes order of 1 m by using the DGPS and of less than 10 m by using the single GPS, if we measure the distance from several positions at the sea surface by using a transponder system which is not designed for the precise ranging. The geometry of calling positions is most important to determine the OBS position, even if we use the data with larger error, such as the direct water wave arrival data. The 1D acoustic velocity structure should be required for the correct depth of the OBS. Although it is rare that we use a CTD, even an empirical velocity structure works well.     

Particulate n-alkanes and fatty acids in the Changjiang river system

Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease (0.84% ～ 1.88%) of organic carbon content from the upper reaches to the estuary.δ13C values of particulate organic carbon was in the range of -24.9×10-3 to -26.6×10-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ13C and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs (soil organic matter) among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream.     

Silting in the Lower Courses of Tidal Sluices in China

Serious sediment deposition often occurs after the construction of tidal sluices in snrall or medium-sized tidal muddy estuaries, so desilting or dredging is needed to meet the demands of flood diseharge, saltwater retaining, and navigation in those areas. In this paper, the problem of sediment deposition induced by construction of tidal sluices is analyzed.Different problems of silting near tidal sluices for different types of estuaries are summed up. at the same time, corresponding methods are given to solve these probleras, and a few successful examples are also given. The idea of comprehensive regulation and utilization of estuaries is put forward, and some proposals for solution of sediment deposition in this kind of estuaries are made.     

River Classification as a Geographic Tool in the Age of Big Data and Global Change

Spatial classification is a well‐defined analysis method in geography, which involves defining regions of the Earth based on shared characteristics. An analogy can be made between classification in geography and taxonomy in biology, because both are used to reduce complexity. Just as modern evolutionary theory and genetics technologies have transformed biological taxonomy from the sometimes arbitrary classification of living things based on superficial similarities and differences into a system that reflects the history of life and relationships among organisms, modern advances in conceptual understanding and development of technology have similarly revolutionized classification in geography as a powerful method for describing and quantifying processes. Here, I describe the history and current trends of geographic classifications relevant to river systems. Overall, there is significant emerging potential in classification as a tool for understanding river processes     

郁江南宁17场洪水之合成面雨量特征分析

对郁江南宁 17场洪水的合成面雨量分布特征作了较系统的分析 ,发现引发南宁洪水的主要天气系统及其配置、合成面雨量的流域值及“6 8.8”大洪水和“0 1.7”特大洪水的合成面雨量表征 ,对今后进一步做好重大洪水的气象服务具有十分积极的意义