Development and Test of Hydrostatic Extraction Scheme in Spectral Model

The introduction of 'hydrostatic extraction' scheme, or 'standard stratification approximation', into spectral model gained some advantages compared with commonly used schemes. However, computational instability may occur for high vertical resolution versions if the stratification parameter C0 taken as a constant. In this paper, the possible cause leading to the instability is discussed and an improved scheme presented where C0 is generalized to be a function of both height and latitudes. Hence the reference atmosphere gets closer to the real atmosphere and the temperature deviation field to be expanded becomes smoother everywhere. Test by real case forecasts shows good computational stability of the new scheme and better prediction performance than-usual schemes of spectral model.

An Impact of Hydrostatic Extraction Scheme on BMRC's Global Spectral Model

There are two important features in geophysical fluid dynamics. One is that the atmospheric and oceanic equations of motion include the Coriolis force; another is that they describe a stratified fluid. The hydrostatic extraction scheme, or standard stratification approximation, posed by Zeng (1979), reflects the second aspect of geophysical fluid dynamics. There exist two major advantages in this scheme; accurate computation of the pressure gradient force can be obtained over steep mountain slopes, and the accumulation error in vertical finite differencing can be reduced, especially near the tropopause.Chen et al (1987) introduced the hydrostatic extraction scheme into a global spectral model, which attained preliminary success at low resolution. Zhang and Sheng et al (1990) developed and improved the hydrostatic extraction scheme in a global spectral model, in which C0, the parameter that represents the stratification of the reference atmosphere, changes not only with height, but also with latitude. The scheme has been incorporated BMRC's global spectral model (IAPB). Four 5-day forecasts have been performed to test the IAPB with the hydrostatic extraction scheme. Objective verifications demonstrate a positive effect of the hydrostatic extration scheme on BMRC's model, particularly at upper levels, over the tropics and the Antartic region.

Fractionation and Soil-Plant Transfer of ^(241)Am in Different Soil Types

Monitoring the behavior of radioactive contaminants associated with military applications,nuclear power facilities,and interim storage of radioactive waste materials is of significant concern in radiological analysis.Four sequential extraction schemes(SES) for fractionation of ^(241)Am were compared using five different types of soils,Vertisol,Cambisol,Chromic Luvisol,Eutric Fluvisol,and mixed urban soil,collected from different parts of Bulgaria.The results for the exchangeable ^(241) Am were in a wide range and depended on the SES used.Soil ^(241)Am varied from 0.5%to 6%in the exchangeable phase,from 0.5%to 35%in the carbonate phase,from0.4%to 36%in the reducible phase(easily reducible and moderately reducible),from 3%to 17%in the oxidizable phase,and from10%to 50%in the residual phase.After 100 d of contamination,around 50%of soil ^(241)Am was permanently fixed in the residual phase.There was strong evidence that the preferable soil phase for ^(241) Am was the carbonate phase.The transfer factor of ^(241) Am in the soil-plant system depended on ^(241)Am in the easily oxidizable phase(fulvic acid(FA)+humic acid(HA) phase).These confirmed the applicability of the National Institute of Standards and Technology(NIST) sequential extraction scheme for fractionation of soil^(241) Am since it includes extraction of FA+HA phase and then the carbonate phase.