A finite element prediction model with variable element sizes

There are a variety of meteorological forecast problems which require high spatial resolution in only a limited area. An important example of this type of problem is the prediction of tropical cyclones. This study tests a simple finite element prediction model with a variable element size. The shallow water equations are used and the motion is confined in a periodic channel on a f-plane. The Galerkin technique is applied to linear basis functions on triangular elements. The model uses leapfrog time differencing and periodic restarts. The model is tested with a wave imbedded in a mean flow and also with an isolated vortex. The experiments with a uniform element size show excellent phase propagation, but some small scale noise is generated. The introduction of momentum diffusion terms helps to control the noise. The model is also tested with elements which decrease abruptly in scale along a line with elements which decrease smoothly. Both of these cases generate more noise than with uniform elements. (Author)