Giant aeolian dune size determined by the average depth of the atmospheric boundary layer

Abstract

Depending on the wind regime, sand dunes exhibit linear, crescent-shaped or star-like forms resulting from the interaction between dune morphology and sand transport. Small-scale dunes form by destabilization of the sand bed with a wavelength (a few tens of metres) determined by the sand transport saturation length. The mechanisms controlling the formation of giant dunes, and in particular accounting for their typical time and length scales, have remained unknown. Using a combination of field measurements and aerodynamic calculations, we show here that the growth of aeolian giant dunes, ascribed to the nonlinear interaction between small-scale superimposed dunes, is limited by the confinement of the flow within the atmospheric boundary layer. Aeolian giant dunes and river dunes form by similar processes, with the thermal inversion layer that caps the convective boundary layer in the atmosphere acting analogously to the water surface in rivers. In both cases, the bed topography excites surface waves on the interface that in turn modify the near-bed flow velocity. This mechanism is a stabilizing process that prevents the scale of the pattern from coarsening beyond the resonant condition. Our results can explain the mean spacing of aeolian giant dunes ranging from 300 m in coastal terrestrial deserts to 3.5 km. We propose that our findings could serve as a starting point for the modelling of long-term evolution of desert landscapes under specific wind regimes.

Recent developments in planetary Aeolian studies and their terrestrial analogs

“…The growing number of spacecraft contributing to the exploration of Mars necessarily focuses considerable attention on the study of Mars, but the dunes on Titan have been receiving increasing attention since their discovery by the Cassini spacecraft in 2004. The spacing of large terrestrial linear dunes may reflect the average depth of the atmospheric boundary layer (Andreotti et al, 2009), which could have considerable relevance to abundant the linear dunes on Titan, but Mars appears to have a dearth of linear dunes. Global monitoring by the Mars Color Imager (MARCI) is documenting changes across the Red Planet for both climatological and meteorological studies, tracking movement of water ice and dust clouds and providing insights into the atmospheric dynamics related to dust lifting (Malin et al, 2008).…”

Wrinkle to fold transition: influence of the substrate response

“…[2][3][4] These structures appear in various contrasted contexts such as during the formation of large-scale structures in the Universe, 5 during thermal convection in uids, Taylor-Couette ow, solidication fronts, oscillatory chemical reactions, 6 during formation of dunes, sand ripples and beach cusps, [7][8][9] during collisions of ice oes, 10 during formation of icicles, hot-spring landscapes and columnar jointing [11][12][13][14] or in minerals like agates. 15 In biology, it is important to know whether the various genetically encoded forms displayed in living organisms are related to physical processes.…”

Observation and Modeling of Interrupted Pattern Coarsening: Surface Nanostructuring by Ion Erosion

“…Actually, an open question in pattern formation at large concerns identifying general criteria [8] to predict the type of evolution of ' [9], ranging from remaining a constant, to power-law behavior, interrupted coarsening (IC), or spatiotemporal chaos. In particular, IC has arisen as a novel type of dynamic behavior whose relevance to, e.g., formation of giant Aeolian sand dunes has been recently invoked [10]. Although in its original formulation IC refers to a pattern that stops growing in ''lateral'' size (') while perpetually increasing in ''vertical'' size (amplitude), more recently other systems have been identified in which an analogous interruption of wavelength and amplitude occur, yielding to kinetic roughening at the largest time and length scales [11,12].…”