Aerodynamic Parameters Over an Eroding Bare Surface: Reconciliation of the Law of the Wall and Eddy Covariance Determinations

Dupont, Sylvain; Rajot, Jean-Louis; Labiadh, Mohamed; Bergametti, Gilles; Alfaro, Stéphane C.; Bouet, Christel; Fernandes, Royston; Khalfallah, B.; Lamaud, Éric; Marticorena, Béatrice; Bonnefond, JM; Chevaillier, Servanne; Garrigou, Didier; Henry-des-Tureaux, Thierry; Sekrafi, Saâd; Zapf, Pascal

doi:10.1029/2017jd027984

Cited by 23 publications

(59 citation statements)

References 37 publications

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“…As expected, the number of impacting saltating particles recorded by the Saltiphone (Figure e) and the size‐resolved particle number concentration measured by the particle spectrometer (Figure f) vary both as the wind speed (Figure b) for surface friction velocity u ∗0 higher than the threshold friction velocity (0.22 ms −1 as deduced in Dupont et al, ; Figure c). Hence, particles detected by the spectrometer are most likely mineral dust resulting from wind erosion.…”

Section: The Wind‐o‐v's 2017 Experimentssupporting

confidence: 83%

“…The main meteorological and dust concentration characteristics of these six events are presented in Figure . All events occurred during daytime; they are thus mainly located on the convective side of the near‐neutral stability conditions (−0.2 < z / L < 0.01, as defined in Dupont et al, ; Figure d). The events exhibit different wind directions (Figure a): west for the 14 April event, northwest for the 7–9 March events, and northeast for the 16 and 20 April events.…”

Section: The Wind‐o‐v's 2017 Experimentsmentioning

confidence: 96%

“…(b) Saltation flux Q against the surface friction velocity ( u ∗0 ) obtained for the 7–9 March, 14 and 15 March, and 20 April events. The fitted curve in (b) corresponds to the parameterization of Lettau and Lettau () with c = 0.7 (see Dupont et al, ). The saltation flux was not measured during the 14 and 16 April events.…”

Section: The Wind‐o‐v's 2017 Experimentsmentioning

confidence: 99%

See 2 more Smart Citations

Dissimilarity Between Dust, Heat, and Momentum Turbulent Transports During Aeolian Soil Erosion

et al. 2019

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Measuring accurately size‐resolved dust flux near the surface is crucial for better quantifying dust losses by semiarid soils. Dust fluxes have been usually estimated from the flux‐gradient approach, assuming similarity between dust and momentum turbulent transport. This similarity has, however, never been verified. Here we investigate the similarity between dust (0.3 to 6.0 μm in diameter), momentum, and heat fluxes during aeolian erosion events. These three fluxes were measured by the Eddy Covariance technique during the WIND‐O‐V (WIND erOsion in presence of sparse Vegetation's) 2017 field experiment over an isolated erodible bare plot in South Tunisia. Our measurements confirm the prevalence of ejection and sweep motions in transporting dust as for heat and momentum. However, our measurements also reveal a different partition of the dust flux between ejection and sweep motions and between eddy time scales compared to that of momentum and heat fluxes. This dissimilarity results from the intermittency of the dust emission compared to the more continuous emission (absorption) of heat (momentum) at the surface. Unlike heat emission and momentum absorption, dust release is conditioned by the wind intensity to initiate sandblasting. Consequently, ejection motions do not carry dust as often as heat and low momentum from the surface. This dissimilarity diminishes with increasing wind intensity as saltation patterns, and thus dust emission through sandblasting, become spatially more frequent. Overall, these findings may have implications on the evaluation of dust flux from techniques based on similarity with momentum or heat turbulent transport.

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Section: The Wind‐o‐v's 2017 Experimentssupporting

confidence: 83%

Section: The Wind‐o‐v's 2017 Experimentsmentioning

confidence: 96%

Section: The Wind‐o‐v's 2017 Experimentsmentioning

confidence: 99%

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Dissimilarity Between Dust, Heat, and Momentum Turbulent Transports During Aeolian Soil Erosion

et al. 2019

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“…However, EC F wd appears less correlated with u * and U at 1 min, and even more at 10-s resolution, than the WT F wd . The best improvement occurs for the 20 April event, which is characterized by a northeastern winds with a possible limited fetch effect for this wind direction as explained in Dupont et al (2018). Although F wd appears slightly better correlated at small time resolution with the near-surface u * than with the 3.0-m high one, F wd is still better correlated with U, with a correlation coefficient of about 0.20 higher than that with the 1.0-m-high u * .…”

Section: Scaling Of the Vertical Dust Fluxmentioning

confidence: 94%

“…The ground surface was flat, with a roughness length around 10 −4 m, and the soil was typical of the Jeffara basin with a surface loamy sand layer very prone to wind erosion (Dupont et al, 2018). The ground surface was flat, with a roughness length around 10 −4 m, and the soil was typical of the Jeffara basin with a surface loamy sand layer very prone to wind erosion (Dupont et al, 2018).…”

Section: Datamentioning

confidence: 99%

Scaling of Dust Flux With Friction Velocity: Time Resolution Effects

Dupont

2020

JGR Atmospheres

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The intermittency of aeolian soil erosion has motivated studies to extend to small time resolution (less than 15-30 min) the scaling property of erosion fluxes with the friction velocity u * . However, common methods used to estimate u * such as the law of the wall or the eddy covariance are only valid for stationary conditions, that is, long periods of 15-30 min. Unlike these methods, the wavelet transform method is applicable for nonstationary conditions. Here, this method is used to investigate the scaling property of the dust flux F wd with u * at 1-min and 10-s resolutions, during erosion events. At 15-min resolution, u * and F wd estimated from the wavelet transform are identical to those obtained by eddy covariance. At smaller resolution, u * and F wd exhibit strong fluctuations around their 15-min trend, reflecting the nonstationarity of the flow and the intermittency of dust emission, respectively. While the 15-min resolution F wd appears as correlated with u * as with the mean wind speed U, with decreasing resolution, F wd becomes less correlated with u * but still significantly correlated with U. Our results suggest that u * is a suitable scaling parameter of F wd over usual 15-to 30-min periods with the advantage of being height independent compared to U. However, at small time resolution, U becomes more relevant to scale F wd , the surface friction velocity becoming hardly accessible due to the absence of a constant momentum flux layer. Our study demonstrates the suitability of the wavelet transform to estimate dust fluxes at small time resolution or during nonstationary events.

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Cross‐wavelet analysis of coherent wind and saltation events

Ellis

Sherman

2022

Earth Surf Processes Landf

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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 À1 , and the average saltation rates are 5.0 and 22.2 counts/mm 2 s À1 , respectively. Normalized crosscovariance 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.

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Aerodynamic Parameters Over an Eroding Bare Surface: Reconciliation of the Law of the Wall and Eddy Covariance Determinations

Cited by 23 publications

References 37 publications

Dissimilarity Between Dust, Heat, and Momentum Turbulent Transports During Aeolian Soil Erosion

Dissimilarity Between Dust, Heat, and Momentum Turbulent Transports During Aeolian Soil Erosion

Scaling of Dust Flux With Friction Velocity: Time Resolution Effects

Cross‐wavelet analysis of coherent wind and saltation events

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