The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Yuan Shen - One of the best experts on this subject based on the ideXlab platform.
-
measurements of aerodynamic roughness bowen ratio and atmospheric surface layer height by eddy covariance and tethersonde systems simultaneously over a heterogeneous rice paddy
Journal of Hydrometeorology, 2010Co-Authors: Jenglin Tsai, Ben-jei Tsuang, Posheng Lu, Kenhui Chang, Yuan ShenAbstract:The aerodynamic roughness, Bowen ratio, and Friction Velocity were measured over a rice paddy using tethersonde and eddy covariance (EC) systems. In addition, the height ranges of the atmospheric inertial sublayer (ISL) were derived using the tethersonde data. Comparison of the Friction Velocity, latent and sensible heat fluxes, and Bowen ratio estimated from these systems show their correlation coefficients to be .0.7. This difference between the observational systems can be associated with their respective footprint areas. The aerodynamic roughness was observed to be about 0.03 m for wind blowing from a paddy-dominated area (PDA) and about 0.37 m from a rice paddy interspersed with buildings (PIB) based on the ISL profile. Results are close to the effective roughness length model of Mason, having the same shear stresses at the blending height. In contrast, both the geometric mean model of Taylor and the arithmetic mean model of Tsai and Tsuang underestimate the effective roughness over the PIB. During daylight hours, the height range of the ISL ranged from a few meters to 25 m above ground level (AGL) for wind blowing from the PDA and 14‐42 m for wind blowing from the PIB.
-
measurements of aerodynamic roughness bowen ratio and atmospheric surface layer height by eddy covariance and tethersonde systems simultaneously over a heterogeneous rice paddy
Journal of Hydrometeorology, 2010Co-Authors: Jenglin Tsai, Ben-jei Tsuang, Kenhui Chang, Minghwi Yao, Yuan ShenAbstract:Abstract The aerodynamic roughness, Bowen ratio, and Friction Velocity were measured over a rice paddy using tethersonde and eddy covariance (EC) systems. In addition, the height ranges of the atmospheric inertial sublayer (ISL) were derived using the tethersonde data. Comparison of the Friction Velocity, latent and sensible heat fluxes, and Bowen ratio estimated from these systems show their correlation coefficients to be >0.7. This difference between the observational systems can be associated with their respective footprint areas. The aerodynamic roughness was observed to be about 0.03 m for wind blowing from a paddy-dominated area (PDA) and about 0.37 m from a rice paddy interspersed with buildings (PIB) based on the ISL profile. Results are close to the effective roughness length model of Mason, having the same shear stresses at the blending height. In contrast, both the geometric mean model of Taylor and the arithmetic mean model of Tsai and Tsuang underestimate the effective roughness over the PIB....
Jayne Belnap - One of the best experts on this subject based on the ideXlab platform.
-
on the prediction of threshold Friction Velocity of wind erosion using soil reflectance spectroscopy
Aeolian Research, 2015Co-Authors: Cody B Flagg, Gregory S Okin, Thomas H Painter, Kebonye Dintwe, Jayne BelnapAbstract:Abstract Current approaches to estimate threshold Friction Velocity (TFV) of soil particle movement, including both experimental and empirical methods, suffer from various disadvantages, and they are particularly not effective to estimate TFVs at regional to global scales. Reflectance spectroscopy has been widely used to obtain TFV-related soil properties (e.g., moisture, texture, crust, etc.), however, no studies have attempted to directly relate soil TFV to their spectral reflectance. The objective of this study was to investigate the relationship between soil TFV and soil reflectance in the visible and near infrared (VIS–NIR, 350–2500 nm) spectral region, and to identify the best range of wavelengths or combinations of wavelengths to predict TFV. Threshold Friction Velocity of 31 soils, along with their reflectance spectra and texture were measured in the Mojave Desert, California and Moab, Utah. A correlation analysis between TFV and soil reflectance identified a number of isolated, narrow spectral domains that largely fell into two spectral regions, the VIS area (400–700 nm) and the short-wavelength infrared (SWIR) area (1100–2500 nm). A partial least squares regression analysis (PLSR) confirmed the significant bands that were identified by correlation analysis. The PLSR further identified the strong relationship between the first-difference transformation and TFV at several narrow regions around 1400, 1900, and 2200 nm. The use of PLSR allowed us to identify a total of 17 key wavelengths in the investigated spectrum range, which may be used as the optimal spectral settings for estimating TFV in the laboratory and field, or mapping of TFV using airborne/satellite sensors.
-
a simple method to estimate threshold Friction Velocity of wind erosion in the field
Geophysical Research Letters, 2010Co-Authors: Gregory S Okin, Jayne Belnap, Jeffrey E Herrick, Seth M Munson, Mark E MillerAbstract:[1] This study provides a fast and easy-to-apply method to estimate threshold Friction Velocity (TFV) of wind erosion in the field. Wind tunnel experiments and a variety of ground measurements including air gun, pocket penetrometer, torvane, and roughness chain were conducted in Moab, Utah and cross-validated in the Mojave Desert, California. Patterns between TFV and ground measurements were examined to identify the optimum method for estimating TFV. The results show that TFVs were best predicted using the air gun and penetrometer measurements in the Moab sites. This empirical method, however, systematically underestimated TFVs in the Mojave Desert sites. Further analysis showed that TFVs in the Mojave sites can be satisfactorily estimated with a correction for rock cover, which is presumably the main cause of the underestimation of TFVs. The proposed method may be also applied to estimate TFVs in environments where other non-erodible elements such as postharvest residuals are found.
-
factors controlling threshold Friction Velocity in semiarid and arid areas of the united states
Journal of Geophysical Research, 1997Co-Authors: Beatrice Marticorena, Dale A Gillette, G Bergametti, Jayne BelnapAbstract:A physical model was developed to explain threshold Friction velocities u*t for particles of the size 60–120 μm lying on a rough surface in loose soils for semiarid and arid parts of the United States. The model corrected for the effect of momentum absorption by the nonerodible roughness. For loose or disturbed soils the most important parameter that controls u*t is the aerodynamic roughness height z0. For physical crusts damaged by wind the size of erodible crust pieces is important along with the roughness. The presence of cyanobacteriallichen soil crusts roughens the surface, and the biological fibrous growth aggregates soil particles. Only undisturbed sandy soils and disturbed soils of all types would be expected to be erodible in normal wind storms. Therefore disturbance of soils by both cattle and humans is very important in predicting wind erosion as confirmed by our measurements.
Yaping Shao - One of the best experts on this subject based on the ideXlab platform.
-
a note on the stochastic nature of particle cohesive force and implications to threshold Friction Velocity for aerodynamic dust entrainment
Aeolian Research, 2016Co-Authors: Yaping Shao, Martina KloseAbstract:Abstract There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold Friction Velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold Friction Velocity scatters strongly due to stochastic inter-particle cohesion. In the real world, there always exists a certain amount of free dust which can be easily lifted from the surface by weak winds or even turbulence, as exemplified by dust devils. It has been proposed in the dust-devil research community, that the pressure drop at dust-devil center may be a major mechanism for dust-devil dust emission, known as the Δp effect. It is questioned here whether the Δp effect is substantial or whether the elevated dust concentration in dust devils is due to free dust emission. A simple analysis indicates that the Δp effect appears to be small and the dust in dust devils is probably due to free dust emission and dust convergence. To estimate free dust emission, it is useful to define a lower limit of dust-particle threshold Friction Velocity. A simple expression for this Velocity is proposed by making assumptions to the median and variance of inter-particle cohesive force. The simple expression is fitted to the data of the Arizona State University Vortex Generator. While considerable uncertainty remains in the scheme, this note highlights the need for additional research on the stochastic nature of dust emission.
-
a simple expression for wind erosion threshold Friction Velocity
Journal of Geophysical Research, 2000Co-Authors: Yaping ShaoAbstract:Threshold Friction Velocity u*t is the Friction Velocity at which wind erosion is initiated. While u*t is affected by a range of surface and soil properties, it is a function of particle size only for idealized soils. In this paper we present a simple expression for u*t for spherical particles loosely spread over a dry and bare surface. In this expression we consider the balance between the driving forces (aerodynamic drag and lift) and the retarding forces (cohesion and gravity) and assume that the cohesive force is proportional to particle size. It is found that u*t can be expressed as Y1d+Y21d, with Y1 and Y2 being empirical constants. The new expression is both simple and effective.
Jenglin Tsai - One of the best experts on this subject based on the ideXlab platform.
-
measurements of aerodynamic roughness bowen ratio and atmospheric surface layer height by eddy covariance and tethersonde systems simultaneously over a heterogeneous rice paddy
Journal of Hydrometeorology, 2010Co-Authors: Jenglin Tsai, Ben-jei Tsuang, Posheng Lu, Kenhui Chang, Yuan ShenAbstract:The aerodynamic roughness, Bowen ratio, and Friction Velocity were measured over a rice paddy using tethersonde and eddy covariance (EC) systems. In addition, the height ranges of the atmospheric inertial sublayer (ISL) were derived using the tethersonde data. Comparison of the Friction Velocity, latent and sensible heat fluxes, and Bowen ratio estimated from these systems show their correlation coefficients to be .0.7. This difference between the observational systems can be associated with their respective footprint areas. The aerodynamic roughness was observed to be about 0.03 m for wind blowing from a paddy-dominated area (PDA) and about 0.37 m from a rice paddy interspersed with buildings (PIB) based on the ISL profile. Results are close to the effective roughness length model of Mason, having the same shear stresses at the blending height. In contrast, both the geometric mean model of Taylor and the arithmetic mean model of Tsai and Tsuang underestimate the effective roughness over the PIB. During daylight hours, the height range of the ISL ranged from a few meters to 25 m above ground level (AGL) for wind blowing from the PDA and 14‐42 m for wind blowing from the PIB.
-
measurements of aerodynamic roughness bowen ratio and atmospheric surface layer height by eddy covariance and tethersonde systems simultaneously over a heterogeneous rice paddy
Journal of Hydrometeorology, 2010Co-Authors: Jenglin Tsai, Ben-jei Tsuang, Kenhui Chang, Minghwi Yao, Yuan ShenAbstract:Abstract The aerodynamic roughness, Bowen ratio, and Friction Velocity were measured over a rice paddy using tethersonde and eddy covariance (EC) systems. In addition, the height ranges of the atmospheric inertial sublayer (ISL) were derived using the tethersonde data. Comparison of the Friction Velocity, latent and sensible heat fluxes, and Bowen ratio estimated from these systems show their correlation coefficients to be >0.7. This difference between the observational systems can be associated with their respective footprint areas. The aerodynamic roughness was observed to be about 0.03 m for wind blowing from a paddy-dominated area (PDA) and about 0.37 m from a rice paddy interspersed with buildings (PIB) based on the ISL profile. Results are close to the effective roughness length model of Mason, having the same shear stresses at the blending height. In contrast, both the geometric mean model of Taylor and the arithmetic mean model of Tsai and Tsuang underestimate the effective roughness over the PIB....
Nico Schulte - One of the best experts on this subject based on the ideXlab platform.
-
estimating the height of the nocturnal urban boundary layer for dispersion applications
Atmospheric Environment, 2012Co-Authors: Sam Pournazeri, Akula Venkatram, Marko Princevac, Si Tan, Nico SchulteAbstract:We analyzed three data sets to examine methods to estimate the height of the stable boundary layer (SBL) in the complex setting of an urban area. We focused on a data set from a field study that we conducted in Riverside, California, in 2011 in which surface micrometeorological variables were measured using a sonic anemometer. In addition, profiles of temperature and relative humidity were measured with a tethersonde up to a height of 500 m. These measurements, supplemented with data from other field studies, were used to evaluate representative diagnostic and prognostic models for the SBL height. As expected, these models performed poorly in the spatially inhomogeneous setting of the urban area. The time integrated Friction Velocity (u*), with time starting at sunset, provided the best estimate of the height. This formulation is useful because we show that the surface Friction Velocity can be estimated with a measurement of wind speed at one height, and an estimate of the surface roughness length.
