Fig. 5: Comparison between data and predictions.

The coarsest grain sizes \(\max ({d}^{({{{{{{{\rm{f}}}}}}}})})\) and \(\max ({d}^{({{{{{{{\rm{c}}}}}}}})})\) are extracted from the left and right margins, respectively, of the coarse-grain peaks of the empirical GSDs (Methods). For a given measurement site, with a given measured size \(\max ({d}^{({{{{{{{\rm{f}}}}}}}})})\) of the coarsest saltating grains, the theoretically predicted size \(\max ({d}^{({{{{{{{\rm{c}}}}}}}})})\) of the coarsest reptating grains is plotted against its measured value. The solid line corresponds to perfect agreement with the idealized model, and the dashed lines indicate a relative error of 20%. See main text for plausible origins of the scatter in the data and suggestions for more accurate measurement protocols. The displayed data is from megaripples located at Nahal Kasuy, Ktora and Yahel in the southern Negev, Israel (filled circles)^16,20,22 (Figs. S4–6); Wadi Rum in southern Jordan (open squares)¹⁶; Sanshan Desert in western China (filled diamonds)^6,16; Antarctica (filled pentagons)¹⁵; Sossusvlei in Namibia (crossed circles) (Fig. S7); Ladakh in India (crosses) (Fig. S8); New Mexico (open triangles)⁴⁰; and Mars (stars)⁴⁰ (Methods). Wind tunnel data are from ref. ²⁰.