TY - JOUR

T1 - A two-concentric-loop iterative method in estimation of displacement height and roughness length for momentum and sensible heat

AU - Zhao, Wenguang

AU - Qualls, Russell J.

AU - Berliner, Pedro R.

N1 - Funding Information:
Acknowledgments This research was partially supported by the German–Israeli Science agreements [Project Number: 01314 (GR) DISUM 00028 (MG)] and partially supported through the NSF-Idaho EPSCoR Program. We wish to thank the late Arieh Rogel and Yossi Goldstein (Mashash Farm, Ben-Gurion University of the Negev, Israel) for their technical support.

PY - 2008/11/1

Y1 - 2008/11/1

N2 - A two-concentric-loop iterative (TCLI) method is proposed to estimate the displacement height and roughness length for momentum and sensible heat by using the measurements of wind speed and air temperature at two heights, sensible heat flux above the crop canopy, and the surface temperature of the canopy. This method is deduced theoretically from existing formulae and equations. The main advantage of this method is that data measured not only under near neutral conditions, but also under unstable and slightly stable conditions can be used to calculate the scaling parameters. Based on the data measured above an Acacia Saligna agroforestry system, the displacement height (d0) calculated by the TCLI method and by a conventional method are compared. Under strict neutral conditions, the two methods give almost the same results. Under unstable conditions, d0 values calculated by the conventional method are systematically lower than those calculated by the TCLI method, with the latter exhibiting only slightly lower values than those seen under strictly neutral conditions. Computation of the average values of the scaling parameters for the agroforestry system showed that the displacement height and roughness length for momentum are 68% and 9.4% of the average height of the tree canopy, respectively, which are similar to percentages found in the literature. The calculated roughness length for sensible heat is 6.4% of the average height of the tree canopy, a little higher than the percentages documented in the literature. When wind direction was aligned within 5° of the row direction of the trees, the average displacement height calculated was about 0.6 m lower than when the wind blew across the row direction. This difference was statistically significant at the 0.0005 probability level. This implies that when the wind blows parallel to the row direction, the logarithmic profile of wind speed is shifted lower to the ground, so that, at a given height, the wind speeds are faster than when the wind blows perpendicular to the row direction.

AB - A two-concentric-loop iterative (TCLI) method is proposed to estimate the displacement height and roughness length for momentum and sensible heat by using the measurements of wind speed and air temperature at two heights, sensible heat flux above the crop canopy, and the surface temperature of the canopy. This method is deduced theoretically from existing formulae and equations. The main advantage of this method is that data measured not only under near neutral conditions, but also under unstable and slightly stable conditions can be used to calculate the scaling parameters. Based on the data measured above an Acacia Saligna agroforestry system, the displacement height (d0) calculated by the TCLI method and by a conventional method are compared. Under strict neutral conditions, the two methods give almost the same results. Under unstable conditions, d0 values calculated by the conventional method are systematically lower than those calculated by the TCLI method, with the latter exhibiting only slightly lower values than those seen under strictly neutral conditions. Computation of the average values of the scaling parameters for the agroforestry system showed that the displacement height and roughness length for momentum are 68% and 9.4% of the average height of the tree canopy, respectively, which are similar to percentages found in the literature. The calculated roughness length for sensible heat is 6.4% of the average height of the tree canopy, a little higher than the percentages documented in the literature. When wind direction was aligned within 5° of the row direction of the trees, the average displacement height calculated was about 0.6 m lower than when the wind blew across the row direction. This difference was statistically significant at the 0.0005 probability level. This implies that when the wind blows parallel to the row direction, the logarithmic profile of wind speed is shifted lower to the ground, so that, at a given height, the wind speeds are faster than when the wind blows perpendicular to the row direction.

KW - Displacement height

KW - Momentum

KW - Roughness length

KW - Scaling parameters

KW - Sensible heat

KW - Two-concentric-loop iterative method

UR - http://www.scopus.com/inward/record.url?scp=54349106621&partnerID=8YFLogxK

U2 - 10.1007/s00484-008-0181-4

DO - 10.1007/s00484-008-0181-4

M3 - Article

AN - SCOPUS:54349106621

SN - 0020-7128

VL - 52

SP - 849

EP - 858

JO - International Journal of Biometeorology

JF - International Journal of Biometeorology

IS - 8

ER -