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首页> 外文期刊>Journal of the Atmospheric Sciences >A Simplified Model for Intermittent Turbulence in the Nocturnal Boundary Layer
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A Simplified Model for Intermittent Turbulence in the Nocturnal Boundary Layer

机译：夜间边界层间歇湍流的简化模型

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A model for the exchange between the surface and the atmosphere under stable conditions is proposed. It is based on the classical scheme first suggested by Blackadar and comprises prognostic equations for the wind components and air and ground temperature. The main difference from previous works consists in the fact that the turbulent intensity is determined by a prognostic equation for turbulent kinetic energy (TKE), rather than by using stability functions that arbitrarily relate it to atmospheric stability. Results show that the model reproduces the condition of connection and disconnection between the surface and upper levels. Furthermore, it leads to periodic turbulence bursts when one level within the stable boundary layer (SBL) is considered and the use of additional levels increasingly leads to more complex solutions, characterizing the occurrence of global intermittency. Such turbulence bursts occur in the disconnected state and cause large fluctuations of the variables near the surface. The boundary layer height plays a role in the sense that for the same geostrophic winds, connection is favored for shallower layers. Although playing a role in the intermittency characteristics, soil type is not determinant to their existence, as the bursts occur even for very high values of heat capacity. Vertical profiles for both the intermittent and connected state are analyzed and in general agree with observations. It is shown that, near the surface, weak turbulence bursts favor the exchange between the air and the cooler ground, leading to a local temperature decrease, while stronger events that mix the air deeper in the SBL cause an average warming tendency. An opposite pattern occurs at the upper SBL. Intermittency is favored over a range of low geostrophic winds and clear skies, in agreement with previous suggestions. The vertical structure of the intermittent events is analyzed, and it shown that they are generated at the surface by a local shear increase above a threshold, propagating upward through the turbulence transfer term in the TKE equation. It is proposed that such events constitute a natural characteristic of the disconnected SBL, which occurs along with low large-scale winds and clear skies.
机译：提出了稳定条件下地表与大气交换的模型。它基于Blackadar最初提出的经典方案，并包括风分量以及空气和地面温度的预测方程。与先前工作的主要区别在于，湍流强度是由湍动能（TKE）的预后方程式确定的，而不是通过将其任意关联到大气稳定性的稳定性函数来确定的。结果表明，该模型再现了表面和上层之间的连接和断开状态。此外，当考虑到稳定边界层（SBL）中的一个层级时，它会导致周期性的湍流爆发，并且使用附加层级会越来越导致更复杂的解决方案，这是全局间歇性发生的特征。这种湍流爆发在断开状态下发生，并导致表面附近变量的较大波动。对于相同的地转风，边界层的高度起着一定的作用，较浅的层有利于连接。尽管在间歇性特征中发挥作用，但土壤类型并不能决定土壤的存在，因为即使热容值很高时也会发生破裂。分析了间歇状态和连接状态的垂直剖面，并且总体上与观察结果一致。结果表明，在地表附近，弱湍流爆发有利于空气与较凉爽的地面之间的交换，从而导致局部温度下降，而在SBL内更深处混合空气的较强事件导致平均变暖趋势。相反的图案出现在上部SBL处。与先前的建议相一致，间歇性优于低地转风和晴朗的天空。对间歇事件的垂直结构进行了分析，结果表明，这些事件是在地面上通过高于阈值的局部剪力增加而生成的，并通过TKE方程中的湍流传递项向上传播。提出这样的事件构成了断开的SBL的自然特征，它伴随着低比例的大风和晴朗的天空而发生。

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