EVENT DETECTION AND CONDITIONAL AVERAGING IN UNSTEADY AEOLIAN SYSTEMS

Traditional models of sediment flux ignore wind unsteadiness, and ther e are sound empirical and theoretical arguments that implicate this de ficiency as being fundamental to explaining their limited predictive a bilities. Drawing on concepts and theories from the fluid mechanics li terature on turbulent boundary layers, and with the implementation of fast-response instrumentation (hot-film anemometers and continuously-w eighing sand traps) this study begins to address a series of inter-rel ated questions regarding the character of wind and transport events. F oremost among these is whether an event-based analysis of wind speed t ime series bears close resemblance to sediment flux events. The resear ch demonstrates that fluid 'ejection' events identified by the Variabl e-Interval Time Averaging (VITA) method are only crudely associated wi th those identified using the quadrant-threshold method. Moreover, VIT A events show poor correspondence with sediment flux events. The reaso ns for this are unclear, although it is likely that the character of e vents in this beach boundary layer differ substantively from the chara cter of structural events typically associated with the sublayer burst ing process. Additional unresolved issues include whether the inner/ou ter layer model applies to the grain-laden/ grain-free zones of a salt ation system, and whether the structural events evident in velocity ti me series from wind tunnels and natural beaches are analogous. Event-d etection and conditional-averaging techniques hold promise for charact erizing the fundamental nature of unsteadiness in aeolian systems. (C) 1998 Academic Press Limited.