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161.
Modeling nonhydrostatic atmospheric flow requires the solution of the vertical equation of motion and a prognostic or diagnostic equation for pressure. If the nonhydrostatic components of the flow are relatively small, they can be approximated and incorporated into a purely hydrostatic model, which usually is conceptually simpler and computationally more efficient. A method to do this for a linear model of local thermally-induced circulations is further developed and adapted to a non-linear numerical model of the neutral atmospheric boundary layer. A hydrostatic model and the quasi-nonhydrostatic version were used to simulate neutral flow over simple terrain features. One set of observations taken over a simple change in roughness and another set taken over a change in both roughness and terrain were simulated by both models to assess the capabilities of the quasi-nonhydrostatic technique.It is found that (as expected) the pressure deviation from the hydrostatic state is negligible for the roughness change, but it is an important aspect of neutral flow over terrain. Thus, for flow encountering a simple roughness change, the hydrostatic approximation is good, even for small horizontal scales. However, the quasi-nonhydrostatic model qualitatively produces the features in the observations for flow over a terrain change that the hydrostatic model cannot produce.Journal Paper No. J-12737 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2779.  相似文献   
162.
The Fe(II)-catalysed transformation of synthetic schwertmannite, ferrihydrite, jarosite and lepidocrocite to more stable, crystalline Fe(III) oxyhydroxides is prevented by high, natural concentrations of Si and natural organic matter (NOM). Adsorption isotherms demonstrate that Si adsorbs to the iron minerals investigated and that increasing amounts of adsorbed Si results in a decrease in isotope exchange between aqueous Fe(II) and the Fe(III) mineral. This suggests that the adsorption of Si inhibits the direct adsorption of Fe(II) onto the mineral surface, providing an explanation for the inhibitory effect of Si on the Fe(II)-catalysed transformation of Fe(III) minerals. During the synthesis of lepidocrocite and ferrihydrite, the presence of equimolar concentrations of Si and Fe resulted in the formation of 2-line ferrihydrite containing co-precipitated Si in both cases. Isotope exchange experiments conducted with this freeze-dried Si co-precipitated ferrihydrite species (Si-ferrihydrite) demonstrated that the rate and extent of isotope exchange between aqueous Fe(II) and solid 55Fe(III) was very similar to that of 2-line ferrihydrite formed in the absence of Si and which had not been allowed to dry. In contrast to un-dried ferrihydrite formed in the absence of Si, Si-ferrihydrite did not transform into a more crystalline Fe(III) mineral phase over the 7-day period of investigation. Reductive dissolution studies using ascorbic acid demonstrated that both dried Si-ferrihydrite and un-dried 2-line ferrihydrite were very reactive, suggesting these species may be major contributors to the rapid release of dissolved iron following flooding and the onset of conditions conducive to reductive dissolution in acid sulphate soil environments.  相似文献   
163.
Urban and suburban storm water runoff from ten locations in eastern Massachusetts was analyzed for 39 polycyclic aromatic hydrocarbons (PAHs) compounds. Similar profiles in PAH composition were observed for groups of samples and appear to reflect land use. The largest group includes, urban storm water from areas with a mix of industrial, commercial, and residential use. Fluoranthene, phenanthrene, pyrene, chrysene, and benzo (b) fluoranthene were the predominant compounds in this group, but lighter molecular weight PAHs were also present. Sources of PAHs to storm water include a combination of petroleum and combustion. The profile of PAH compounds in local atmospheric deposition was similar to urban storm water, but differed in several of the predominant compounds. PAHs in storm water could increase the levels of these compounds in nearshore sediments and may be the most important source of high molecular weight PAHs to these environments.  相似文献   
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