Roger Luff, Andreas Moll, and Thomas Pohlmann
Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung,
Universität Hamburg, Germany
A PC-based animation program is now available free of charge on the World Wide Web to study simulation results from three-dimensional numerical models of the North Sea. Two versions of this program, one for DOS and the other for Windows 3.x / WIN95 operating systems are available. The program can animate 12 scenarios from four different models, and it demonstrates annual changes in the hydrography and regional productivity of the North Sea through cinema-like moving pictures. During the animation, specific colors represent the concentrations of the simulated parameters at the surface layer. The models used are developed in the German project KUSTOS, which analyzes and quantifies matter, heat, and water fluxes from land through the German Bight into the shelf sea.
A free copy of the program is available on the WWW server: http://ifmaix7.ifm.uni-hamburg.de/kino.html.
The underlying flow fields for all simulations are based on results of a three-dimensional baroclinic primitive equation North Sea model [Pohlmann, 1996]. The driving forces of this model are weekly sea surface temperatures, climatological salinity distributions, and surface wind stress and air pressure fields measured every 3 hours. The model covers the region from 55 01'W to 13 55'E and from 48 53'N to 61 41'N with a meridional spacing of 12 min and a zonal spacing of 20 min. The vertical dimension is resolved by 19 layers with a resolution of 5 m per layer in the upper 50-m depth for an accurate description of the thermocline dynamics. The animation of the sea surface temperature, the sea surface elevation, and the salinity distribution are results from this model.
Fig. 1. A still photo of the animation of the sea surface temperature of the North Sea.
The inflow of water from the open boundaries into the North Sea is calculated with a three-dimensional Eulerian transport model to estimate the influence of the different water masses into the North Sea [Luff and Pohlmann, 1995]. The water entering through the open boundaries of the North Sea is marked with a passive conservative tracer to allow viewers to follow the dispersion of the specific water masses.
The simulations clearly demonstrate the dominance of the North Atlantic water mass in the North Sea. About 85% of water in the North Sea originates from this source, whereas water from the English Channel and the Baltic Sea only account for about 3% each. The influence of both the English Channel and the North Sea is only remarkable in some specific regions like the Skagerrak for the Baltic Sea inflow or the Southern Bight for the Channel inflow. The variability of the weather systems has a decisive impact on the distribution and the motion of the water masses as well as on the dispersion of matter. The resulting fluctuations are prominent in all the animations.
Fig. 2. A still photo of the animation of the inflow of North Atlantic water in the North Sea.
The annual cycles of phytoplankton, phosphate, and daily cumulated primary production are estimated with a three-dimensional primary production model [Moll, 1997]. The advection-diffusion-reaction model uses the hydrographical flow field of Pohlmann [1996] to calculate the transport processes of the biological variables. Phosphate regeneration occurred in the pelagic zone through a simple parameterization at the bottom via a benthic detritus pool. Solar radiation was calculated every 30 min for each grid point by a model using daily cloud data. The underwater light is reduced by shading of the phytoplankton. Primary production is limited in the model by solar radiation, the nutrient phosphate, and zooplankton grazing.
The animation of the surface layer shows the annual cycles of horizontal concentrations of two main variables of the pelagic plankton environment in the North Sea: phosphate and phytoplankton. The animation of the evolution and the spatial distribution of phytoplankton exhibits the migration of the spring bloom from the coast to the central North Sea following the bathymetry. The evolution of phosphorus characterizes the phase of depletion that migrates from the coast of Norway into the North Sea following the onset of stratification.
Fig. 3. A still photo of the animation of the phosphate concentration of the North Sea.
The third animation from the primary production model shows the cumulated daily primary production in this area through the end of the year. The total depth-integrated production shows enormous regional differences and ranges between 92 and 345 g cm-2 y-1 with lowest values in the central northern North Sea and highest values off the Netherlands coast and in the German Bight.
Additional animations from a German Bight model operated by R. Schmidt-Nia (ZMK-Hamburg) are available on the WWW server that demonstrate the variability of the program VISUMOD.
The minimal hardware and software requirements for the program "KINO" Version 1.1 (DOS-version) are a DOS version greater than 3.2, a 80286 or higher processor, a VGA graphic card, Mouse and Microsoft compatible mouse driver and about 4-Mbyte of hard disc space. Minimal hard and software requirements for the program "VISUMOD" Version 2.1 (WINDOWS-version) are WINDOWS 3.x or WIN95 / NT, a 80386 or higher processor, a VGA graphic card with at least 256 colors, Mouse and Microsoft compatible mouse driver, and about 4-16 Mbytes (depends on the data in the package) hard disc space. Contact Roger Luff (luff@geomar.de) for further information about a separate program for building your own animations for VISUMOD.
Contact Andreas Moll for further information about the models at the Institut für Meereskunde, Troplowitzstr. 7, D-22529 Hamburg; (moll@ifm.uni-hamburg.de). A free copy of the program and the data sets described above are available on the World Wide Web server: http://ifmaix7.ifm.uni-hamburg.de/kino.html.
Luff, R., and T. Pohlmann, Calculation of the water exchange times in the ICES-Boxes with an Eulerian dispersion model using a half-life time approach, Deutsche Hydrographische Zeitschrift, 47(4), 287-299, 1995.
Moll, A., Modeling primary production in the North Sea, Oceanography, 10, in press, 1997.
Pohlmann, T., Predicting the thermocline in a circulation model of the North Sea, Part I, Model description, calibration and verification, Cont. Shelf Res., 16(2), 131-146, 1996.
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