Study Of Statistical-dynamical Parameterization Scheme On Regional Evapotranspiration Flux Over Complex Land Surface

The numerical simulation of the land surface process has been focused on as the climatic effects of it have been further studied recently, and the parameterization schemes about land surface flux have been researched broadly. The real land surface is of multiple scales heterogeneity, which controls the exchanges of air-land momentum, heat flux, water vapor and other green house gases. There are many factors that may influence the land surface process such as: the different terrains, land use, vegetation canopy, soil nature, even the differences of the land-air energy and water exchanges under small scales, local or sub-grid meteorological, hydrologic and biologic conditions. Thus, it is necessary to discuss the parameterization schemes of the land surface process, especially of the heterogeneous ones.The zone of the lower reaches of the Yangtze River is focused in this paper, spanning from 118 E to 123 E, 28 N to 33 N. The focused area is of typical moist climatic region, with complex topography, such as: water land, drought land, woodland, lakes, grassland and towns. The spatial and temporal distribution of the land-air energy and mass flux is complicate.First, based on the satellite data (NOAA-AVHRR) and conventional observations,the land surface temperature and soil humidity of the above area is retrieved. The soil humidity is retrieved by revising the thermal inertia involving the vegetation canopy. The split-window techniques are used to pick-up the remote sensing information of the land surface temperature. All numerical experiments are passed the statistically confidential testSecond, on the basis of the retrieved data of soil water content and land surface temperature, the probability density functions (PDF) of them fitted. The statistically confidential tests of the fitted and the retrieved data are conducted, of which the fitted distribution obeys 0 -distribution and tested by t-test.Third, based on the parameterization of the related land surfacecharacteristics, using the probability density functions(PDF) and the grossly dynamic resistance method , a statistical-dynamical parameterization scheme is put forward. The mean evapotranspiration flux of lower reaches of the Yangtze River is calculated by tins scheme and the results are compared with the formers' conclusions.Finally, the calculated results by the statistical-dynamical parameterization scheme are compared with the Mosaic method. The theoretical analysis and the numerical experiments are done to validate the feasibility of the scheme.Conclusions are drawn as follows:1. Using improved thermal inertia method, which considers the land surface vegetation canopy , soil humidity is retrieved more exactly than the original method. The new method is convenient for calculating the land surface turbulence flux over Heterogeneous terrains.2. There is some error to calculate the factor flux by grid mean as compared with by each patch(such as Mosaic method). The error is related to the two rank partial derivative of the flux function to each factor and the mean variance distribution of each factor on each grid point. The statistical-dynamical parameterization scheme involves the both conditions, therefore, it is more practical for the East China moist region than the Mosaic method.