Micrometeorological fluxes under the influence of regional and local advection: a revisit

This paper presents a new analysis of inequality of eddy diffusivities for sensible heat (KH) and water vapor (KW). It is shown that the same set of equations, established on the principle of dual-source diffusion, can be applied to both local and regional advection. Various advection scenarios are discussed using a formula that relates KH/KW to the Bowen ratio of the advective source and the observed gradient Bowen ratio (βg) near the ground surface. A similar analysis can also be performed for eddy diffusivities for trace gases. The ratio KH/KW, observed at a well-watered wheat field in the North China Plains, was mostly greater than unity when βg was negative and smaller than unity when βg was positive. The pattern was consistent with the theoretical analysis of the ratio under the influence of regional advection. Some degree of local advection was also suggested by the data. Despite inequality of the eddy diffusivities, there was little systematic bias between the evapotranspiration rates measured with a Bowen ratio/energy balance and an eddy covariance system.