Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed‐Up Effect

We study the morphodynamics of reversing dunes on gravel deposits alluvial fan Molcha river at border between Tibetan Plateau and Taklamakan Desert. Independent sets wind data show that this area low sand availability is exposed to two prevailing winds from opposite directions different strengths. The predicted resultant transport direction particles westward. Nevertheless, satellite observations combined with field measurements ground-penetrating radar surveys reveal isolated a few meters high migrate eastward. This apparent dune migration paradox resolved using numerical analytical models take into account speed-up effect continuous change in shape after each reversal. When newly established hits what was before steeper lee slope dune, flux crest abruptly increases relaxing back constant value as migrates downwind reaches new steady shape. Integrated over entire cycle, we find non-linear behavior causes against direction. reflects difference seen by irregular storm events blowing east westward daily cycle. Thus, explore impact extreme examine aspects permanent feedback topography speed. conclude transient behaviors associated reversals contribute observed diversity patterns, even within same for sizes.