Cross‐wavelet analysis of coherent wind and saltation events

• Published in: Earth surface processes and landforms Vol. 48; no. 2; pp. 406 - 414
• Main Authors: Ellis, Jean T., Sherman, Douglas J.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2023
• Subjects: aeolian geomorphology; Analysis; Field tests; Intervals; Response time; Saltation; Sand; Sand transport; Sediment transport; Statistical analysis; Time series; unsteadiness; Wavelet analysis; wavelet events; Wind measurement; Wind speed; Brazil; Australia
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.5493

This paper presents high‐resolution field measurements of the wind and saltation fields using miniphones and anemometers located 20–40 mm apart (bed‐parallel) and 10–40 mm above the bed. The average wind speeds at the Shoalhaven Heads, Australia and the Jericoacoara, Brazil field sites are both 4.4 m s−1, and the average saltation rates are 5.0 and 22.2 counts/mm2 s−1, respectively. Normalized cross‐covariance analysis between the wind and saltation time series indicates a dominant saltation response time of 0 s. Cross‐wavelet analysis focusing on short‐duration events characterizes statistically significant wind–sand events and intervals. In the high aeolian saltation rate environment (Brazil), the events and intervals averaged 1.9 and 12.2 s. The low transport environment (Australia) resulted in 2.1 s events and 10.8 s intervals. This study demonstrates that wind–sand events occur about 15% of the time but account for about 23% of the sand transport. These results were possible because of the presentation of a wavelet‐derived event time series. The criticality of tightly controlled field experiments to measure coincident wind and saltation fluctuations with co‐located sensors was demonstrated. This paper emphasizes the importance of the contribution of saltation events to time‐averaged transport rates, which influences sediment flux modelling. Closely spaced, fast sampling miniphones and thermal anemometers measured saltation and wind fluctuations to determine a dominant saltation response time of 0 s. Cross‐wavelet analysis identified simultaneous wind–sand events that enabled the generation of a novel event time series. During active saltation, events comprise 22.5% of all the saltation and occur 14.7% of the time.