00-159 Hiroshi Momiji, Ricardo Carretero-Gonz\'{a}lez, Steven R Bishop and Andrew Warren

The effect of wind speedup in the formation of transverse dune fields (107K, Postscript (no figures)) Apr 4, 00

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Abstract. A computer simulation model for transverse-dune-field dynamics, corresponding to a uni-directional wind regime, is developed. In a previous formulation, two distinct problems were found regarding the cross-sectional dune shape, namely the erosion in the lee of dunes and the steepness of the windward slopes. The first problem is solved by introducing no erosion in shadow zones. The second issue is overcome by introducing a wind speedup factor, which can be accounted for by adding a term to the original transport length, which is proportional to the surface height. By incorporating these features we are able to model dunes whose individual shape and collective patterns are similar to those observed in nature. Moreover we show how introducing a non-linear wind speedup term leads to the reduction of dune height, and this may result in an equilibrium dune field configuration. This is thought to be because the non-linear wind speedup makes the sand trap efficiency lower than unity, even for higher dunes, so that the incoming and the outgoing sand flux are in balance. Finally we discuss the formation of the inter-dune flat surface arising from the existence of shadow zones.

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