simulations in this article will try to answer some questions and justify the importance of further field measurements.

First some general aspects will be introduced. A model for dunes in three dimensions will show why translational invariance appears in transverse dune formation. The time evolution and the dune velocity in a two dimensional model with constant sand influx will be presented. The time evolution of a model of two dimensional dunes with periodic boundary conditions will give some more insight into dune field dynamics. A final discussion of the statement that dunes behave like solitons will close this article.

General aspects of transverse dunes {#sec:trans_intro}
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About 40% of all terrestrial sand seas are covered by transverse dunes. They are mostly located in sand seas where sand is available. Thus in larger sand seas one mainly finds ensembles of many transverse dunes which interact with respect to their dynamics. The crest to crest spacing ranges from a few meters to over 3 km [@Breed79]. They are common in the Northern Hemisphere, for example in China, and along coasts. On Mars transverse dunes dominate the sand seas.

![An aerial photo (STS047–153A–263) of transverse dunes in Lop Nur, China. Image courtesy of 