Numerical Simulation of Mountain Waves over the Southern Andes. Part I: Mountain Wave and Secondary Wave Character, Evolutions, and Breaking
Numerical Simulation of Mountain Waves over the Southern Andes. Part I: Mountain Wave and Secondary Wave Character, Evolutions, and Breaking
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DOI：
10.1175/jas-d-19-0356.1
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发表时间：
2020-12
影响因子：
3.1
通讯作者：
T. Lund;D. Fritts;K. Wan;B. Laughman;Han L. Liu
中科院分区：
文献类型：
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作者：
T. Lund;D. Fritts;K. Wan;B. Laughman;Han L. Liu
本文讨论了冬季条件下，伴随着南安第斯山脉上山波(MW)强迫增加并传播到中间层和低热层(MLT)的可压缩非线性动力学。拉伸的网格在很大的计算域中提供了非常高的MW动力学分辨率。跨山风的缓慢增加使MWs最初在中间层破裂，然后延伸到越来越低和更高的高度。微波结构和破裂受静态平均和半日潮汐的强烈调制，在~114公里处出现了一个纬向微波传播的临界值。对于不同纬向波长的λx，不同的垂直群速度在λx~50 km的安第斯山脉主峰的背风处产生初始破裂，并在随后较大的λx接近临界水平时向上游显著延伸。安第斯山脉地形在纬度上的局部化程度导致早期在个别峰值上方产生“船浪”响应，而随着更大尺度的兆瓦获得更大的振幅，在100公里及以上的地方会有更大的船浪响应。微波破碎区域上方的其他响应包括大规模的次级重力波和声波，这些波的幅度非常大，延伸到热层。微波破裂还会导致动量沉积，最初会产生局部减速，然后合并并水平延伸，并持续整个事件。相关论文研究了相关的动量通量、平均流演变、重力波-潮汐相互作用、微波不稳定动力学以及二次重力波和声波的来源。
This paper addresses the compressible nonlinear dynamics accompanying increasing mountain wave (MW) forcing over the southern Andes and propagation into the mesosphere and lower thermosphere (MLT) under winter conditions. A stretched grid provides very high resolution of the MW dynamics in a large computational domain. A slow increase of cross-mountain winds enables MWs to initially break in the mesosphere and extend to lower and higher altitudes thereafter. MW structure and breaking is strongly modulated by static mean and semidiurnal tide fields exhibiting a critical level at ~114 km for zonal MW propagation. Varying vertical group velocities for different zonal wavelengths λx yield initial breaking in the lee of the major Andes peaks for λx ~ 50 km, and extending significantly upstream for larger λx approaching the critical level at later times. The localized extent of the Andes terrain in latitude leads to “ship wave” responses above the individual peaks at earlier times, and a much larger ship-wave response at 100 km and above as the larger-scale MWs achieve large amplitudes. Other responses above regions of MW breaking include large-scale secondary gravity waves and acoustic waves that achieve very large amplitudes extending well into the thermosphere. MW breaking also causes momentum deposition that yields local decelerations initially, which merge and extend horizontally thereafter and persist throughout the event. Companion papers examine the associated momentum fluxes, mean-flow evolution, gravity wave–tidal interactions, and the MW instability dynamics and sources of secondary gravity waves and acoustic waves.