In 1988 L.L.Takacz introduced the flow over an isolated mountain as a test problem for the shallow water equations (SWE). After Williamson et.al. added it as fifth test case to the NCAR test suite for the SWE many researchers investigated this problem.

One of the big challenges for the next generation of global circulation models (GCM) will be adaptive meshes. The most suitable test case for this kind of grid generation out of the test suite is test case 5. Because of this it will become more and more important to understand the inherent problems of test case 5.

We investigate test case 5 with three different models (GME, SEAM, FEMmE) and compare the results. Depending on the model we observe different problems. After the discussion of them we will propose an additional test and a modified mountain to get a deeper understanding of the model numerics.