Contribution of Low-Frequency Motions to Sensible Heat Fluxes over Urban and Suburban Areas

Field observations of the atmospheric boundary layer were made over urban and suburban terrain in the Yangtze River Delta, China. A multiresolution decomposition was applied over three different types of terrain: flat homogeneous terrain, suburban terrain and urban terrain, with results indicating that, (1) the average scale contribution of u, v, w and $$T_{v}$$Tv had a similar variability with length scale for all these three sites respectively, and the dimensionless length scale corresponding to the maximum sensible heat flux contribution increased with the terrain complexity; (2) the length scale corresponding to the maximal average scale contribution for vertical wind velocity $$\lambda _w $$λw was directly proportional to the roughness length $$z_{0}$$z0 in unstable conditions; and (3) the contributions of large-scale motions led to sensible heat fluxes determined with a large-aperture scintillomter being larger than those using the eddy-covariance method for the suburban case, whereas this phenomenon was not substantial for the urban case.