Quasiperiodic saltation in the windsand flux over desertified area
G.I. Gorchakov, A.V. Karpov, G.A. Kuznetsov, D.V. Buntov
A.M. Obukhov Institute of Atmospheric Physics Russian Academy of Sciences, Pyzhevsky per., 3, 119017, Moscow, Russia
Keywords: опустынивание, ветропесчаный поток, механизм сальтации, концентрация сальтирующих песчинок, квазипериодические вариации концентрации, длительность цугов, мгновенная частота, струйная сальтация, когерентность пульсаций скорости ветра, desertification, windsand flux, saltation mechanism, saltating sand concentration, quasiperiodic variations of concentration, wave packet duration, instantaneous frequency, jet saltation, wind velocity pulsation coherence
Abstract
Saltation mechanism investigation in the windsand flux over the desertified area has been carried out on fast video recording data using spectral and wavelet analysis. Quasiperiodic variation peculiarities of the saltating sand concentration are studied. It is established that narrow bands in spectrum (“spectral lines”) of saltating sand concentration fluctuation density power in the range from 100 to 200 Hz are consistent with wave packets, which duration achieves 8-9 periods. It is suggested to use the duration of the wave packets observed as a measure of a pulsation coherence of the wind velocity in a near surface layer of the atmosphere. It is shown that quasiperiodic variability saltating sand concentration appearance is explained by interaction of the wind gusts with wave irregularities on the underlying surface type of fine ripples. The wave packet formation with duration to 4-5 periods can be explained using the model of jet-pulse saltation.
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