Modeling the diurnal cycle of conserved and reactive species in the convective boundary layer
Modeling the diurnal cycle of conserved and reactive species in the convective boundary layer
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模拟对流边界层中保守物种和活性物种的昼夜循环
DOI：
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发表时间：
2015
期刊：
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通讯作者：
E. Patton
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作者：
D. Lenschow;D. Gurarie;E. Patton
我们已经开发了一个一维二阶闭合数值模式来研究对流（白天）行星边界层（CBL）中痕量活性物质的垂直湍流输送，我们称之为守恒和反应非定常标量的二阶模型（SOMCRUS）。CBL深度的时间变化计算使用一个简单的混合层模式与恒定的夹带系数和零阶不连续的CBL顶部。然后，我们计算随时间变化的连续配置文件的平均浓度和垂直湍流通量，方差和协方差的保守和化学反应标量在一个昼夜变化的CBL。反应性物种的集合是O3-NO-NO2三元组。保守和活性物种的结果进行了比较大涡模拟（LES）相同的自由对流的情况下，使用相同的边界和初始条件。对于保守的物种，我们比较了三种情况下，不同的组合的表面通量，CBL和自由对流层浓度。我们发现很好的协议SOMCRUS与LES的平均浓度和通量的保守和反应的物种，除了附近的CBL顶部，SOMCRUS预测有点浅的深度，并在平均值和湍流变量急剧过渡，相比之下，更多的涂抹出的变化，由于水平平均LES。此外，SOMCRUS通常低估了方差和种-种协方差。SOMCRUS预测的温度物种协方差相似LES附近的表面，但小得多的幅度峰值附近的CBL顶部，和变化的协方差的符号非常接近CBL顶部，而LES预测的协方差的符号变化在下半部分的CBL。SOMCRUS还能够估计分离的强度（种-种协方差与其平均值的乘积的比率），这可以改变二级化学反应的速率;然而，对于这里考虑的情况，这种影响很小。SOMCRUS的简单性和可扩展性意味着它可以用于广泛的混合情景和行星边界层中的化学反应;因此，它作为将这些过程纳入空气质量和气候模型的工具具有很大的希望。
We have developed a one-dimensional secondorder closure numerical model to study the vertical turbulent transport of trace reactive species in the convective (daytime) planetary boundary layer (CBL), which we call the SecondOrder Model for Conserved and Reactive Unsteady Scalars (SOMCRUS). The temporal variation of the CBL depth is calculated using a simple mixed-layer model with a constant entrainment coefficient and zero-order discontinuity at the CBL top. We then calculate time-varying continuous profiles of mean concentrations and vertical turbulent fluxes, variances, and covariances of both conserved and chemically reactive scalars in a diurnally varying CBL. The set of reactive species is the O3–NO–NO2 triad. The results for both conserved and reactive species are compared with large-eddy simulations (LES) for the same free-convection case using the same boundary and initial conditions. For the conserved species, we compare three cases with different combinations of surface fluxes, and CBL and free-troposphere concentrations. We find good agreement of SOMCRUS with LES for the mean concentrations and fluxes of both conserved and reactive species except near the CBL top, where SOMCRUS predicts a somewhat shallower depth, and has sharp transitions in both the mean and turbulence variables, in contrast to more smeared-out variations in the LES due to horizontal averaging. Furthermore, SOMCRUS generally underestimates the variances and species–species covariances. SOMCRUS predicts temperature–species covariances similar to LES near the surface, but much smaller magnitude peak values near the CBL top, and a change in sign of the covariances very near the CBL top, while the LES predicts a change in sign of the covariances in the lower half of the CBL. SOMCRUS is also able to estimate the intensity of segregation (the ratio of the species–species covariance to the product of their means), which can alter the rates of second-order chemical reactions; however, for the case considered here, this effect is small. The simplicity and extensibility of SOMCRUS means that it can be utilized for a broad range of turbulencemixing scenarios and sets of chemical reactions in the planetary boundary layer; it therefore holds great promise as a tool to incorporate these processes within air quality and climate models.