Dune formation under bimodal winds
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF
AMERICA, 106 (52):
22085-22089 (2009)DOI: 10.1073/pnas.0808646106
Abstract
The study of dune morphology represents a valuable tool in the
investigation of planetary wind systems-the primary factor controlling
the dune shape is the wind directionality. However, our understanding of
dune formation is still limited to the simplest situation of
unidirectional winds: There is no model that solves the equations of
sand transport under the most common situation of seasonally varying
wind directions. Here we present the calculation of sand transport under
bimodal winds using a dune model that is extended to account for more
than one wind direction. Our calculations show that dunes align
longitudinally to the resultant wind trend if the angle theta(w) between
the wind directions is larger than 90 degrees. Under high sand
availability, linear self dunes are obtained, the intriguing meandering
shape of which is found to be controlled by the dune height and by the
time the wind lasts at each one of the two wind directions. Unusual dune
shapes including the ``wedge dunes'' observed on Mars appear within a
wide spectrum of bimodal dune morphologies under low sand availability.