Dual-scale transport of sensible heat and water vapor over a short canopy under unstable conditions

Abstract

This study examines the nature of vertical transport of sensible heat and water vapor density due to mesoscale motions and how they are observed with surface eddy covariance systems. For this purpose, turbulence data measured above a flat and irrigated rice paddy field under unstable conditions were analyzed. It was shown that the larger-scale component in the measured time series represents mesoscale motions. Wavelet cospectra of the scalar fluxes revealed the presence of vertical transport at horizontal scales larger than the cospectral gap. A time series and the eddy covariance flux were decomposed into a turbulence and a mesoscale component using the identified cospectral gap. The mesoscale transport component of sensible heat and water vapor were found to be related to the wind direction and therefore characteristic of the upwind surface conditions at this scale. In contrast, the turbulence flux component exhibits universal attributes resulting from the local surface characteristics. Copyright 2007 by the American Geophysical Union.