Large-Eddy Simulation of a Residual Layer: Low-Level Jet, Convective Rolls, and Kelvin–Helmholtz Instability
Large-Eddy Simulation of a Residual Layer: Low-Level Jet, Convective Rolls, and Kelvin–Helmholtz Instability
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残余层的大涡模拟：低水平射流、对流滚转和开尔文-亥姆霍兹不稳定性
DOI：
10.1175/jas-d-13-0402.1
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发表时间：
2014
影响因子：
3.1
通讯作者：
J. Ito and H. Niino
中科院分区：
文献类型：
--
作者：
Nakanishi;M.;R. Shibuya;J. Ito and H. Niino
利用一个包含长波辐射和斜压性的大涡模拟（LES）模式，研究了Wangara实验第33天0900 LST至第34天0600 LST的大气边界层日变化。本研究特别关注残留层（RL）中的现象。随着表面热通量的减少，惯性振荡开始，并伴随着低空急流（LLJ）在大约200米的高度。LLJ的最大风速在第34天0300 LST时超过12 m s− 1。在第33天2100 LST之后，由于LLJ在大尺度水平温度梯度下的水平平流使RL不稳定，从而引起水平对流卷，平行于垂直风切变（VWS）矢量，高度在400和1400米之间。午夜后，在对流卷底部和逐渐增长的LLJ最大值之间的层中的VWS被加强，并且梯度Richardson数福尔斯在第34天0130 LST时在400 m高度处下降到其临界值0.25以下。经验正交函数分析表明，Kelvin-Helmholtz（KH）涡出现在对流卷下方，并与它们耦合。这项研究表明，水平对流卷可以发生在RL，因为LLJ经常平流温暖的空气到低层根据大尺度的温度梯度和辊可能与KH涡共存在一个稳定的边界层，因为LLJ逐渐增加VWS。
Diurnal variations of an atmospheric boundary layer from 0900 LST on day 33 to 0600 LST on day 34 of the Wangara experiment are studied using a large-eddy simulation (LES) model that includes longwave radiation and baroclinicity. The present study directs its particular attention to phenomena in a residual layer (RL). As the surface heat flux decreases, an inertial oscillation is initiated and is accompanied by a low-level jet (LLJ) at a height of approximately 200 m. The maximum wind speed of the LLJ exceeds 12 m s−1at 0300 LST on day 34. After 2100 LST on day 33, the horizontal advection due to the LLJ under a large-scale horizontal gradient of temperature destabilizes the RL and consequently induces horizontal convective rolls, parallel to a vertical wind shear (VWS) vector, between heights of 400 and 1400 m. The VWS in the layer between the bottom of the convective rolls and the gradually growing LLJ maximum is intensified after midnight, and the gradient Richardson number falls below its critical value of 0.25 at a height of 400 m at 0130 LST on day 34. An empirical orthogonal function analysis demonstrates that Kelvin–Helmholtz (KH) vortices appear below the convective rolls and are coupled with them. This study suggests that horizontal convective rolls can occur in an RL because an LLJ often advects warmer air to the lower layer according to a large-scale gradient of temperature and that the rolls may coexist with KH vortices in a stable boundary layer because the LLJ gradually increases a VWS.