The coherent structure of water vapour transfer in the unstable atmospheric surface layer

Observations of water vapour fluctuations over a rice field show vapour ramps. Coherent structures are first revealed by the frequently occurring ramp pattern in the vapour trace. Wavelet and pseudo-wavelet analysis techniques were used in conditional sampling, and more than 100 hr of data have been analyzed to determine coherent structure characteristics. The most probable coherent structure duration was in the range 2-12 sec and the duration range of the most effective coherent structures shows some difference between heat and water vapour transfers. Coherent structures contribute to the major part of the total flux.