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611.
The authors have developed a model to predict the radiation stresses in the coastal zone and to estimate currents and set-up/set-down
of mean sea level. The values of radiation stress are calculated from velocity potential, which can be obtained by analytical
means or from a finite element model of the elliptic extended mild slope equation depending on the complexity of the situation
in question. The values of radiation stress are then input into a hydrodynamic model which gives the resulting set-up/set-down
and currents caused by these stresses. The developed model includes convective acceleration and bottom friction. The radiation
stress results of the model have been compared with analytical results and published values. Results for set-up/set-down and
currents have been compared with published results for seven other similar models. The model has been compared with published
results for set-up/set-down and currents created in the vicinity of a detached breakwater and also around a conical island.
The results of the authors’ model compare well with the analytical results, and published results for similar models.
An erratum to this article can be found at 相似文献
612.
Gerhard?JentzschEmail author Adelheid?Weise Carlos?Rey Carl?Gerstenecker 《Pure and Applied Geophysics》2004,161(7):1415-1431
Temporal gravity changes provide information about mass and/or density variations within and below the volcano edifice. Three active volcanoes have been under investigation; each of them related to a plate boundary: Mayon/Luzon/Philippines, Merapi/Java/Indonesia, and Galeras/Colombia. The observed gravity changes are smaller than previously expected but significant. For the three volcanoes under investigation, and within the observation period, mainly the increase of gravity is observed, ranging from 1,000 nm–2 to 1,600 nms–2. Unexpectedly, the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit. At Mayon and Merapi the parallel GPS measurements yield no significant elevation changes. This is crucial for the interpretation, as the internal pressure variations do not lead to significant deformation at the surface. Thus the classical Mogi-model for a shallow extending magma reservoir cannot apply. To confine the possible models, the attraction due to changes of groundwater level or soil moisture is estimated along the slope of Merapi exemplarily by 2-D modelling. Mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations; the results are compared to the model incorporating the additional effect of elastic deformation. 相似文献
613.
614.
Summary. Estimates of the shape of the sea surface as determined from satellite altiméters have become of increasing importance in geophysics, geodesy and physical oceanography. The most effective error reduction procedures used in producing these surfaces have been some version of a crossing-arc analysis. The problem with this procedure is the absence of an easy means of evaluating the noise structure of the final result. By recasting the problem as one of objective mapping (optimal estimation) we both optimize the error reduction and obtain an explicit estimate of the wave-number structure of the final altimétric surface. Examples, suitable to a small computer, have been generated to show that the error reduction along the sub-satellite tracks is very great, with most of the residual lying in long wavelengths. 相似文献
615.
B.N. Khare Carl Sagan John E. Zumberge Deborah S. Sklarew Bartholomew Nagy 《Icarus》1981,48(2):290-297
The complex dark brown solid of a class called tholins, produced on passage of an electrical discharge through a roughly equimolar mixture of methane and ammonia with 2.6% water vapor, is analyzed by vacuum pyrolysis followed by gas chromatography and mass spectrometry. Pyrolyzates include a wide range of aliphatic and aromatic nitriles, alkanes, aromatic hydrocarbons, pyrrole, and pyridine. This tholin is remarkably stable to 950°C. It and its degradation products are candidate constituents of planetary aerosols in the outer solar system and of the grains in the interstellar medium. 相似文献
616.
617.
We examine a non-linear mechanism for a solar surge in which plasma regions of high electrical conductivity and macroscopic dimension can be rapidly accelerated without diffusion of magnetic field. The mechanism is suggested by Rust's observations, which show that surges occur near sunspots in regions of reversed magnetic polarity. For the purposes of numerical calculation, we replace the magnetic field near a polarity reversal in a sunspot by magnetic fields of current loops. The relaxation of the magnetic field generated by two antiparallel coaxial current loops in an incompressible plasma is traced by computer. The results suggest that plasma in the form of a vortex ring can be expelled at the Alfvén velocity from active solar regions. 相似文献
618.
The recently discovered coorbital satellites of Saturn, 1980S1 and 1980S3, are shown to be librating in horseshoe orbits. By considering the effects of tangential forces on the semimajor axes of the satellite orbits, we derive an accurate relation between the sum of the satellite masses and (a) their minimum angular separation, (b) the variation of their angular separation with time and (c) the libration period. Observations of (b) and (c) are the most practical methods of determining the satellite masses. The orbits of the coorbital satellites of Dione and Tethys are discussed. We demonstrate the possibility of calculating a new value for the mass of Dione and we show that one of the coorbital satellites of Tethys could be moving in a horseshoe orbit even though another satellite is librating in a tadpole orbit about the leading Lagrangian equilibrium point L4. The origin of coorbital satellites and the stability of their orbits are discussed. 相似文献
619.
620.
The mineral dissolution rate conundrum: Insights from reactive transport modeling of U isotopes and pore fluid chemistry in marine sediments 总被引:1,自引:0,他引:1
Pore water chemistry and 234U/238U activity ratios from fine-grained sediment cored by the Ocean Drilling Project at Site 984 in the North Atlantic were used as constraints in modeling in situ rates of plagioclase dissolution with the multicomponent reactive transport code Crunch. The reactive transport model includes a solid-solution formulation to enable the use of the 234U/238U activity ratios in the solid and fluid as a tracer of mineral dissolution. The isotopic profiles are combined with profiles of the major element chemistry (especially alkalinity and calcium) to determine whether the apparent discrepancy between laboratory and field dissolution rates still exists when a mechanistic reactive transport model is used to interpret rates in a natural system. A suite of reactions, including sulfate reduction and methane production, anaerobic methane oxidation, CaCO3 precipitation, dissolution of plagioclase, and precipitation of secondary clay minerals, along with diffusive transport and fluid and solid burial, control the pore fluid chemistry in Site 984 sediments. The surface area of plagioclase in intimate contact with the pore fluid is estimated to be 6.9 m2/g based on both grain geometry and on the depletion of 234U/238U in the sediment via α-recoil loss. Various rate laws for plagioclase dissolution are considered in the modeling, including those based on (1) a linear transition state theory (TST) model, (2) a nonlinear dependence on the undersaturation of the pore water with respect to plagioclase, and (3) the effect of inhibition by dissolved aluminum. The major element and isotopic methods predict similar dissolution rate constants if additional lowering of the pore water 234U/238U activity ratio is attributed to isotopic exchange via recrystallization of marine calcite, which makes up about 10-20% of the Site 984 sediment. The calculated dissolution rate for plagioclase corresponds to a rate constant that is about 102 to 105 times smaller than the laboratory-measured value, with the value depending primarily on the deviation from equilibrium. The reactive transport simulations demonstrate that the degree of undersaturation of the pore fluid with respect to plagioclase depends strongly on the rate of authigenic clay precipitation and the solubility of the clay minerals. The observed discrepancy is greatest for the linear TST model (105), less substantial with the Al-inhibition formulation (103), and decreases further if the clay minerals precipitate more slowly or as highly soluble precursor minerals (102). However, even several orders of magnitude variation in either the clay solubility or clay precipitation rates cannot completely account for the entire discrepancy while still matching pore water aluminum and silica data, indicating that the mineral dissolution rate conundrum must be attributed in large part to the gradual loss of reactive sites on silicate surfaces with time. The results imply that methods of mineral surface characterization that provide direct measurements of the bulk surface reactivity are necessary to accurately predict natural dissolution rates. 相似文献