In order to clarify the mechanisms of desertification in semi-arid areas, we measured micro-meteorological characteristics at both a sand dune plot and a vegetation plot in the Hulun Buir Sandy Land, located in the eastern part of the Inner Mongolia, China, in October 1990. The following results were obtained.
1) The thickness of the boundary layer over the dune was more than 5m during night time, and less than 1.5m in daytime, which creates strong shear atress on the dune surface, thus allowing sand to jump away easily and preventing the growth of vegetation.
2) The moisture vapor pressure at 2.5m height was higher than that at 0.5m at the dune, therefore the downward transport of vapor was measured in the mixing layer over dune even though it was daytime.
3) Albedo at the dune was about 40% and that at the vegetation was about 15%. The net radiation, Rn over the dune of 2.95MJ/m2 was much smaller than that over the vegetation which was 8.08MJ/m2.
4) The diurnal share of heat budget components was much different between the dune and vegetation. About 70% of Rn was spent for latent heat, lE, 20% for soil heat, G, and 10% for sensible heat, H, at the vegetation, while at the dune H shared 81%, G shared 29%, and the missing of 10% was supplied by lE from the atmosphere.
5) In the nocturnal share of the heat budget, G was almost equal to Rn at the vegetation, but at the dune Rn was supported by 50% by G, 14% by lE and 26% by H.