Premium
Surface transfer of heat and momentum over an inhomogeneous vegetated land surface
Author(s) -
Hopwood W. P.
Publication year - 1995
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712152704
Subject(s) - roughness length , surface roughness , momentum transfer , homogeneous , surface finish , terrain , momentum (technical analysis) , surface (topology) , heat transfer , mechanics , wind speed , meteorology , wake , flux (metallurgy) , flow (mathematics) , physics , geometry , mathematics , materials science , optics , statistical physics , thermodynamics , wind profile power law , scattering , geography , cartography , finance , metallurgy , economics , composite material
Tethered‐balloon data collected over an inhomogeneous, semi‐rural area of central England are presented. the data are compared with previous surface data to assess how representative fixed‐point flux‐measurements are of area averages. the differences between the data and ‘established’ surface‐layer results are relatively small with departures of about 10% to 20%. This supports the concept of a blending height above which the flow becomes horizontally homogeneous. Effective roughness lengths for momentum and heat transfer are derived. the ratio z eff 0m / z eff 0t is found to be about 80 compared to z 0m / z 0t ≈10 observed for homogeneous terrain. For different wind directions the relationship between the effective roughness length and the upwind surface is investigated using recent theories on the area‐averaging of surface roughness lengths. It is found that the method of averaging transfer coefficients gives realistic values of the effective roughness lengths when compared to observations.