Watershed Scale Shear Stress From Tethersonde Wind Profile Measurements Under Near Neutral and Unstable Atmospheric Stability


Journal Article

Mean wind speed profiles were measured in the atmospheric surface layer, using a tethersonde system, above the Ojai Valley Watershed in southern California. The valley is mainly planted with mature avocado and orange trees. The surface shear stress and latent and sensible heat fluxes were measured above the trees which are up to 9 m in height. Near‐neutral wind speed profile measurements allowed the determination of the watershed surface roughness (z0 = 1.4 m) and the momentum displacement height (d0 = 7.0 m). The wind speed measurements obtained under unstable atmospheric stability were analyzed using Monin‐Obukhov similarity theory. New stability correction functions proposed based on theory and experiments of Kader‐Yaglom as well as the now classic Businger‐Dyer type functions were tested. The watershed shear stress values calculated using the surface layer wind speed profiles with the new Monin‐Obukhov stability functions were found to be improved in comparison with the values obtained with the Businger‐Dyer functions under strongly unstable stability conditions. The Monin‐Obukhov model with the Businger‐Dyer stability correction function underpredicted the momentum flux by 25% under strongly unstable stability conditions, while the new Kader‐Yaglom formulation compared well on average (R2 = 0.77) with the surface eddy correlation measurements for all atmospheric stability conditions. The unstable 100‐m drag coefficient was found to be u*2/V1002 = 0.0182. Copyright 1995 by the American Geophysical Union.

Full Text

Duke Authors

Cited Authors

  • Parlange, MB; Katul, GG

Published Date

  • January 1, 1995

Published In

Volume / Issue

  • 31 / 4

Start / End Page

  • 961 - 968

Electronic International Standard Serial Number (EISSN)

  • 1944-7973

International Standard Serial Number (ISSN)

  • 0043-1397

Digital Object Identifier (DOI)

  • 10.1029/94WR01949

Citation Source

  • Scopus