HOW PERFECT IS PERFECT IN A DUNE-FIELD PATTERN?

Aeolian dune-field patterns arise from the autogenic interactions between dunes within a set of boundary conditions. Over time or space, emergent dune-field patterns evolve toward fewer, larger, and more widely spaced dunes. The hypothetical end product of this pattern coarsening is the “perfect pattern,” where dune crestlines are continuous across the field, and not marred by defects or dune terminations, and all dune interactions have worked their way through the field. Previous studies have shown that the number of defects within fields of crescentic and linear dunes decreases with dune spacing, where spacing is taken as a proxy for time. In this work, the spatial density of dune interactions is measured in fields of linear and crescentic dunes covering the full range of scales on Earth. Results demonstrate that linear and crescentic dune morphologies follow statistically distinct but parallel trends, which can be modeled as an inverse quadratic relationship between interaction density and spacing. However, when parameterized to be expressed in non-dimensional terms, these two curves collapse to a constant and the relative spatial density of interactions (termed the interaction index) does not change with spacing. This implies that dune fields rapidly form patterns dependent on their morphology, and that these patterns are maintained as the pattern coarsens. Agreement between the globally-sampled terrestrial fields, and dune fields on Mars and Titan further suggests that dune field patterns are dependent on dune morphology, and independent of boundary conditions that do not contribute to dune morphology. The constant interaction index across a wide range of natural dune fields appears to arise because the dune interactions are conserved within or propagated through the pattern.