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William K. Dewar 《地球物理与天体物理流体动力学》2013,107(1-4):53-85
Abstract The term ‘‘solitary wave'’ is usually used to denote a steadily propagating permanent form solution of a nonlinear wave equation, with the permanency arising from a balance between steepening and dispersive tendencies. It is known that large-scale thermal anomalies in the ocean are subject to a steepening mechanism driven by the beta effect, while at the smaller deformation scale, such phenomena are highly dispersive. It is shown here that the evolution of a physical system subject to both effects is governed by the ‘‘frontal semi-geostrophic equation'’ (FSGE), which is valid for large amplitude thermocline disturbances. Solitary wave solutions of the FSGE (here named planetons) are calculated and their properties are described with a view towards examining the behavior of finite amplitude solitary waves. In contrast, most known solitary wave solutions belong to weakly nonlinear wave equations (e.g., the Korteweg—deVries (KdV) equation). The FSGE is shown to reduce to the KdV equation at small amplitudes. Classical sech2 solitons thus represent a limiting class of solutions to the FSGE. The primary new effect on planetons at finite amplitudes is nonlinear dispersion. It is argued that due to this effect the propagation rates of finite amplitude planetons differ significantly from the ‘‘weak planeton'', or KdV, dispersion relation. Planeton structure is found to be simple and reminiscent of KdV solitons. Numerical evidence is presented which suggests that collisions between finite amplitude solitary waves are weakly inelastic, indicating the loss of true soliton behavior of the FSGE at moderate amplitudes. Lastly, the sensitivity of solitary waves to the existence of a nontrivial far field is demonstrated and the role of this analysis in the interpretation of lab experiments and the evolution of the thermocline is discussed. 相似文献
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Rachele S. Wilson Kerry Jones Sean Fleischfresser Bridgette Davis Genevieve Jones 《社会与自然资源》2018,31(3):335-350
This article examines roles, opportunities, and challenges for Indigenous land management in rapidly developing landscapes through a case study of Bunya Bunya Country Aboriginal Corporation, a not-for-profit organization on the Sunshine Coast, Queensland, Australia. An analysis of data collected through semistructured interviews, participant observation, and analysis of secondary sources reveals that Aboriginal land managers work in a variety of roles to manage issues affecting the local environment and cultural heritage sites. These efforts are challenged by the absence of Native Title and colonial land management policies, which restrict Aboriginal involvement in land management. We conclude that there is a need for alternative pathways to engage with Aboriginal land managers who cannot, or choose not to, proceed with Native Title. Decolonized decision-making tools and sustainable enterprises are viable opportunities that partially address these challenges and could deliver tangible socio-economic and cultural benefits to local Aboriginal and non-Aboriginal people. 相似文献
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Peter Koenraad Swart Genevieve Healy Lisa Greer Michael Lutz Amel Saied Daniel Anderegg Richard E. Dodge David Rudnick 《Estuaries and Coasts》1999,22(2):384-397
This paper will discuss the use of chemical proxies in coral skeletons to reconstruct the history of salinity (from the δ18O of the skeleton) and nutrients in the water (from the δ13C) in Florida Bay between 1824 and 1994. Monthly salinity and water temperature data collected since 1989 were used to establish a correlation between salinity, temperature, and the δ18O of the skeleton of the coralSolenastrea bournoni from Lignumvitae Basin in Florida Bay. This relationship explains over 50% of the variance in the δ18O of the skeleton. Assuming that interannual variations in the temperature of the water are small, we have applied this relationship to the δ18O measured in the coral skeleton collected from Lignumvitae Basin which has a record between 1824 and 1993. These data provide a revised estimate of salinity variation in Lignumvitae Basin for the period when historical records for salinity were not available, and show that the highest salinity events occurred in the past 30 yr. Using the relationships between the salinity in Lignumvitate Basin and other basins, obtained using a modern dataset, we are able to estimate ranges in salinity for other portions of Florida Bay. Skeletons of specimens of the coral speciesSiderastrea radians collected from other areas of Florida Bay show similar patterns in the δ18O over the past 10 yr, indicating that corals in most portions of Florida Bay are recording salinity variations in their skeletons and therefore support the idea that salinity variations in different portions of Florida Bay can be related. Fluorescence analysis of the coral from Lignumvitae Basin shows a large change in the magnitude of the 10-yr signal coincident with the construction of the railway, confirming that this event had a significant impact upon Florida Bay. The δ13C of the coral skeletons reveals a long-term history of the oxidation of organic material, fixation of carbon by photosynthesis (algal blooms), and the intrusion of marine water into the bay. Since the construction of the railway from Miami to Key West there has been a long-term decrease in the δ13C of the coral skeleton from Lignumvitae Basin, suggesting the increased oxidation of organic material in this area. This decrease in δ13C appears to have reached a minimum value around 1984 and has increased since this time in the western portions of Florida Bay. The increase may be related to the algal blooms prevalent in the area or alternatively could result from intrusion of more marine water. In the eastern areas, a small increase in the δ18C between 1984 and 1988 was followed by further decline suggesting more oxidation of organic material. We have also attempted to use the concentration of barium in the coral skeleton as a proxy indicator of the nutrient status in Florida Bay. 相似文献
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Mitigation of lunar dust adhesion by surface modification 总被引：2，自引：0，他引：2
Adrienne Dove Genevieve Devaud Xu Wang Mark Crowder Anna Lawitzke Christina Haley 《Planetary and Space Science》2011,59(14):1784-1790
Dust has been recognized as one of the greatest hazards in continued lunar exploration due to its tenacious adhesion to everything with which it comes into contact. Unfortunately, there is little known about the mechanisms of adhesion on widely varying surface types: van der Waals and electrostatic forces are the dominant forces under consideration here. Surface energy, roughness, mechanical properties and electronic properties are all known to contribute to the adhesion characteristics. An optimal solution to mitigate dust adhesion would be to identify the dominant components of the adhesive force and to reduce that force by surface modification. In this study, an ion beam process was used to modify (treat) the surfaces of three dramatically different materials spanning the range of conductor (black Kapton), semiconductor (silicon), and insulator (quartz). Adhesive forces between less than JSC-1 lunar simulants and these virgin/treated surfaces were measured in vacuum using a centrifugal force detachment method. We found that JSC-1 particles adhered less to treated silicon and quartz surfaces, correlated with a reduction in van der Waals force due to a reduced surface energy. The large reduction in adhesion for treated black Kapton is mainly due to the large decrease in the electrostatic (image) force that results from reduced contact charging. Materials in space and on the lunar surface will be directly exposed to high-energy ultraviolet radiation prior to being covered by dust, so the UV irradiation effects on surface adhesion were also examined. Both virgin and treated quartz surfaces are most affected by the UV-irradiation, showing dramatically increased adhesion. 相似文献
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All available hydrographic data are used to compute average temperature-salinity, salinity-depth and temperature-depth curves for 5° squares in the North Atlantic and North Pacific (10°S to 60°N). Both objective and subjective methods are used to filter out obviously erroneous data. Summary maps of all 5° square mean curves, and their corresponding standard deviations, are used to select regions of spatial homogeneity over which the curves are averaged. Scatter diagrams of each parameter pair are used to identify 5° squares containing a variety of water masses.The area average curves, and their standard deviations, are presented individually along with tables of the parameter values. These curves, in conjunction with the 5° square summary maps, provide a comprehensive picture of the distributions of these properties in the upper and mid-depth portions of these oceans. This well resolved picture of the water mass structure both confirms and adds new insights into the traditional concepts of these property distributions.The application of the mean temperature-salinity and salinity-depth curves to the inference of salinity from observed temperature profiles, is examined. Shallow (0/500 db) dynamic heights, calculated from observations of temperature and salinity (true dynamic height), are compared with dynamic heights computed from observed temperature profiles and salinities inferred from the mean property curves. Maps of the RMS differences between true and inferred dynamic heights (by 5° square) reveal those areas where salinities, inferred from either temperature-salinity or salinity-depth curves, yield reliable dynamic heights. 相似文献
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Abstract The adjustment of a nonlinear, quasigeostrophic, stratified ocean to an impulsively applied wind stress is investigated under the assumption that barotropic advection of vortex tube length is the most important nonlinearity. The present study complements the steady state theories which have recently appeared, and extends earlier, dissipationless, linear models. In terms of Sverdrup transport, the equation for baroclinic evolution is a forced advection-diffusion equation. Solutions of this equation subject to a “tilted disk” Ekman divergence are obtained analytically for the case of no diffusion and numerically otherwise. The similarity between the present equation and that of a forced barotropic fluid with bottom topography is shown. Barotropic flow, which is assumed to mature instantly, can reverse the tendency for westward propagation, and thus produce regions of closed geostrophic contours. Inside these regions, dissipation, or equivalently the eddy field, plays a central role. We assume that eddy mixing effects a lateral, down-gradient diffusion of potential vorticity; hence, within the closed geostrophic contours, our model approaches a state of uniform potential vorticity. The solutions also extend the steady-state theories, which require weak diffusion, by demonstrating that homogenization occurs for moderately strong diffusion. The evoiution of potential vorticity and the thermocline are examined, and it is shown that the adjustment time of the model is governed by dissipation, rather than baroclinic wave propagation as in linear theories. If dissipation is weak, spin-up of a nonlinear ocean may take several times that predicted by linear models, which agrees with analyses of eddy-resolving general circulation models. The inclusion of a western boundary current may accelerate this process, although dissipation will still play a central role. 相似文献
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The particle trajectories and transport effects of coherent vortices are computed and a number of advection and diffusion experiments using a time-dependent dynamical ring model are analyzed. Several features of the tracer distributions in the numerical solutions are similar to features noted in sea surface temperature images of Gulf Stream rings and are discussed from the point of view of the model. Comparisons between tracer distributions computed using the dynamic ring model and several purely kinematic ring representations demonstrate that most of the important features of ring transport are not altered by slow dynamical evolution. Loss rates from the ring trapped zone are also estimated, which permits calculation of cross-Gulf Stream chemical and biological fluxes due to ring formation. We demonstrate that the salinoty flux to the Slope Water caused by rings is comparable to that caused by the atmosphere.The transport of passive scalars produced by a series of rings moving through a channel (modeling the Slope Water region between the Shelf and the Gulf Stream) is computed. It is found that transport in the along-channel direction is enhanced by the presence of rings and is characterized by Nusselt numbers of 0(30–40). Cross-channel fluxes, while enhanced, are somewhat less affected by rings, and are generally characterized by Nusselt numbers < 0(10). The combined effect of rings on the Slope is seen to make it an anisotropic medium, with along-channel transport one to two orders of magnitude more efficient than cross-channel transport. The implications with respect to the Slope are discussed. 相似文献