A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable. 相似文献
Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.
An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO2 concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO2 concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.
The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion. 相似文献
Seawater samples were collected in the lagoon of Nouméa (southwest New Caledonia) along two transects from eutrophic coastal bays to the oligotrophic barrier reef. Land-based emissions to the lagoon were measured with dissolved and particulate concentrations of chromium (Cr) and nickel (Ni), used as tracers of both terrigenous and industrial (Ni ore treatment) activities, as well as dissolved and particulate concentrations of zinc (Zn), used as a tracer of urban effluents. The spatial variability of metal concentrations was related to geochemical and hydrodynamic conditions, i.e., respectively: (1) natural and anthropogenic emission sources, and chemical processes occurring in the water column; and (2) water residence times. The parameter used to describe the residence time of water masses was the local e-flushing time, i.e. the time required for a tracer mass contained within a given station to be reduced by a factor 1/e. High metal concentrations were found in coastal areas (up to 9000 ng dissolved Ni L−1), and steeply decreased with distance from the coast (down to 101 ng dissolved Ni L−1 near the barrier reef) to reach levels similar to those found in remote Pacific waters, suggesting a rapid renewal of waters close to the barrier. Distributions of metals in the lagoon are controlled upstream by land-based emission sources and later chemical processes. Then hydrodynamics constrain metal distributions, as shown by the observed relationship between local e-flushing times and the spatial variability of metal concentrations. In addition, a change in the direction of prevailing winds yielded a decrease of dissolved metal concentrations at the same site by a factor of 2.5 (Cr and Ni) and 2.9 (Zn). It is suggested that the residence time is a key parameter in the control of elemental concentrations in the lagoon waters, as much as land-based emission sources. 相似文献
Cohort abundance of walleye pollock (Theragra chalcogramma) is subject to strong interannual variation in the eastern Bering Sea, and this variation is known to be determined largely at the age-0 stage. We estimated the spatial distributions and densities of age-0 walleye pollock in five nursery areas around the eastern Bering shelf in three successive years (1997–1999) from acoustic survey data. Concurrently, we calculated estimates of the spatial distribution of euphausiids, a major prey of age-0 walleye pollock, and estimates of spatial overlap of groundfish predators with the age-0 walleye pollock. The analyses showed that all nursery areas had low densities of age-0 walleye pollock in 1997, which ultimately produced the weakest adult year-class. In the intermediate year of 1998, age-0 densities were low to medium, and in 1999, which produced the strongest of the three adult year-classes, all nursery areas had medium to high age-0 walleye pollock densities. Euphausiid distributions had a consistently positive spatial relationship with age-0 walleye pollock. Groundfish predator density ratios were positively related to age-0 walleye pollock density when age-0 walleye pollock were displaced relatively northward. Our results suggest that abundance of age-0 walleye pollock, and hence of adult cohorts in the eastern Bering Sea, can be predictable from a concise set of indicators: the densities of age-0 walleye pollock at nursery areas in mid- to late-summer, their spatial relationship to euphausiids and groundfish predators, and the latitudinal trend of their distributions. The 3 years 1997–1999 had significant differences of physical conditions in the eastern Bering Sea, and represent an advantageous framework for testing these hypotheses. 相似文献