Panjin Reed Wetland Parameterization Scheme

Wetland, forest and ocean ecosystems are the three most important ecosystems in the world. At present, the long-term studies on ecosystem flux exchanges are concentrated in the forest and grassland ecosystems. There are few studies about wetland ecosystems. It restricts the understanding and the accurate estimation of the land-atmosphere flux exchanges in wetland ecosystems.The observations and researches on the land-atmosphere flux exchanges and the construction of the flux network in our country started relatively late. There are only 7 years about eddy correlation observations, and the eddy covariance system is too expensive to popularize. But two height layers'wind speed, temperature and humidity gradient observations started more early and the data were easier to access. Therefore, the estimation of land-atmosphere flux exchanges based on the micrometeorological gradient observation database has become the hot focus. Variational method is often taken as the better method calculating land-atmosphere flux exchanges based on the micrometeorological gradient observation database, which made full use of the boundary layer observational data, Monin-Obukhov similarity theory and the surface energy balance equation.Based on the data from the open eddy correlation system and micrometeorological gradient system in Panjin reed wetland in the years of both 2005 and 2006, a quantitative description of the surface aerodynamic characteristics and their statistical instabilities and their main controlling factors have been analyzed. On this basis, the applicability of B-D stability function was analyzed at this site. Based on the surface aerodynamic parameters and the data from those two systems, the weighting coefficients of variational method and their controls were studied. A method to estimate the weighting coefficients of variational method was proposed. The main conclusions were listed as follows:1) In non-growing season, the zero plane displacement (d) of reed ecosystem can be calculated according to 2/3h at this site as the formula suggested by Garrett. In growing season, d and the height of the plant (h) has a very good linear correlation: d=0.77h. The zero plane displacement is bigger than 2/3h, it's probably caused by a dense reed community in the growing season. z0/h has a quadratic curve correlation with LAI. z0/h firstly decreases rapidly with increasing LAI, then changes very little.2) The atmospheric stability in the atmospheric surface layer of Panjin reed wetland often maintains weak stability and unstability.3) Businger-Dyer stability function parameter schemes could be used in Panjin reed wetland under the atmospheric stability (-0.4< z/L<-0.1). The parameterization scheme in the atmospheric surface layer of Panjin reed wetland needs further study, when the stability function is beyond the range of the atmospheric stability (-0.4< z/L<-0.1).4) This study developed the preliminary statistical method for estimating weighting coefficients of the variational method. The weighting coefficients are various among different months, and they are not only related with the observation error of the instrument, but also related with the height of plant, zero-plane displacement et al.5) Compared with the eddy correlation method, the variational method subjects to the restrictions on energy balance equation, the sum of sensible heat flux and latent heat flux is more concentrated in the vicinity of the effective energy.