Dera Editor Marine Physics 54. The assimilation of 20 and 44 tide-gauges every 6 h results in a very good performance respectively 63 and 68% of model sea-level variance reduction. Using an ensemble method, demonstrated that model error statistics due to uncertainties in bathymetry were non-homogeneous, non-isotropic and swiftly evolving depending on the meteorological regime and the associated oceanic processes at work in the region. These simulated observations are then assimilated in each of the 100 perturbed members of the ensemble and the model error reduction by the assimilation is estimated by comparing the evolution of the ensemble spread with assimilation to the one corresponding to the free simulations. Simulated observations at tide-gauge locations are extracted from this simulation, with an additional 1. The mean reduction of ensemble variances is calculated over the entire North Sea for a 25 day period in December 1998.
Recent volumes in the series cover aspects of chemical, biological and physical oceanography, modelling, operational oceanography, and in-depth regional studies. Figure 2, shows the evolution of the multifractal dimension calculated performing the box-counting algorithm for each level of velocity modulus a and volume fraction b. Global ocean data assimilation of temperature data: preliminary results N. Kjerfve Editor Coastal Lagoon Proceses 61. Following the study of , we focus on the specific model error due to uncertainties in bathymetry.
Both time series of sea-level differences light solid lines are coherent with the variability in the observed cable transport bold solid lines. Lyard, 2001, personal communication is a finite-element, free-surface, barotropic, nonlinear and time-stepping model derived from. Metocean data collection: short-term costs and long-term benefits? Global, full-depth models are in an earlier stage of development, and have not yet demonstrated a general capability to track information across the ocean, or to document its dissipation. In other words, the domain of influence of a tide-gauge observation in this area see also extends more than 100 km away from the station. The oil pollution of the southern Baltic Sea, the North Sea, and the northwestern Mediterranean Sea has been studied within a two-year period from December 1996 until November 1998. Here we will discuss the application of multifractal techniques to detect oil spills and the dynamic state of the sea regarding turbulent diffusion. Footnotes Aikman F, Mellor G.
The strong vertical stratification of the surface water aids the development of the largest vortices. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Figure 8 Ensemble sea-level variance evolution at point 2 without assimilation and with assimilation every 12 h of data from 20 tide-gauges. The reason is that sea-level error at this given time is empirically well correlated over large areas more than 100 km in these high sea-level variances regions. The detailled structure of the front will afect the overall mixing as well as the transport properties between the fluids of different densities subject to gravitational acceleration.
The accuracy of model outputs in the South Atlantic Bight both at coastal and offshore locations is evaluated using tide-gauge observations. Using an advanced assimilation scheme that takes into account the swift evolution of model error statistics, these observations are shown to be very efficient to control model error, provided that they can be assimilated very frequently i. About this Item: Elsevier Science, Amsterdam, 1997. Three of them are located outside regions of high ensemble variances, so that errors in these areas are not likely to be corrected in this configuration. The present state of international cooperation is not yet sufficient to meet the needs of models.
Figure 5 Locations of the stations for the 4, 20 and 44 tide-gauge networks. Takano Editor Oceanography of Asian Marginal Seas 55. Note also that the temporal scales of variations of the ensemble spread are here longer than the ones encountered at the first location closer to the coast peaks lasting 2—3 days, see for further details. The comparison between dye dispersion experiments and model in the surf zone is good, while the outfall predictions show the importance of accurately modelling the effects of buoyancy on the plume. Collins Editors Oceanography and of the Basque Country 71. Figure 10 Histogram synthesizing the space—time global performance of the different observing scenarios, in terms of ensemble sea-level variance reduction over the North Sea for a 25 day period in December 1998.
The model prognostic variables are the salinity, temperature as well as zonal and meridional velocities and barotropic streamfunction. Massel Hydrodynamics of Coastal Zones 49. Therefore, coastal tide-gauge measurements are used in this case as independent sea-level data to assess the model's ability to represent sea-level variability at coastal stations see also ; ; ; for similar experiments with other models. The second application extends the work of on sea-level data assimilation over the European shelf and investigates the contribution of assimilated tide-gauge observations see also ; for previous experiments. Barotropic velocities are more directly controlled by bottom topography which is the perturbed parameter in this study , so that correlations with sea-level are less significant. Figure 9 Ensemble sea-level variance evolution at point 1 without assimilation and with assimilation every 6 h of data from 20 tide-gauges. Global aspects of megascience P.
Sx — Coastal, estuarine, and near shore processes. Innengelenke mit Gewebeband sauber überklebt. As the only non-observed component used in our computation is the offshore model sea-level, we hope that this experiment will allow us to assess the model offshore sea-level realistic behaviour. Operational climate monitoring program of the Arctic ice cover O. The ensemble variance is only reduced by 34%. Only a finer regional model resolving realistic smaller scale forcing and dynamics could achieve a perfect accuracy in these areas. That way, error peaks, which locally have temporal scales of about 1 day due to the swift propagation of gravity waves close to the coast are properly reduced.
A weak relaxation to daily sea surface temperature and seasonal sea surface salinity is applied at the surface. Tide-gauge locations are represented in. Some significant values of the ensemble sea-level variance are then reached during periods of high error growth see peaks around 27 and 31 December. Bc — Computational methods and data processing, data acquisition and storage. A significant improvement of the correction is obtained after assimilation of data coming from 20 tide-gauges c , especially along the Danish coast and at the English Channel entry.
Today, the main limitation for this quasi real-time validation of an operational system by tide-gauge measurements is the real-time delivery of the data, which is not yet sufficient. This allows the investigation of the traces produced by vortices and other features in the ocean surface. The assimilation of tide-gauge data is then liable to properly control sea-level model error along the coasts, provided that the distance between different stations is of the order of the extension of the domain of influence of the coastal observations relative to the type of error under consideration. However, this diagnostic is clearly dependent both on the location inside or outside the domain of influence of the considered tide-gauges and on the temporal scales of variations of the associated sea-level error. They indicate, that these optical parameters support the interpretation of hydrographic and biogeochemical conditions.