Linear mountain drag and averaged pseudo‐momentum flux profiles in the presence of trapped lee waves
Linear mountain drag and averaged pseudo‐momentum flux profiles in the presence of trapped lee waves
复制标题
存在截留背风波时的线性山地阻力和平均伪动量通量剖面
DOI：
--
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
F. Lott
中科院分区：
文献类型：
--
作者：
F. Lott
利用二维线性非弹性模型计算了在背风波存在下的线性山阻力。在许多情况下，表明阻力受高空波折射率的影响，但仍然可以很好地预测由流体静力自由传播的山波引起的阻力。相反，波浪雷诺数应力的垂直剖面对平均流量变化非常敏感，在稳定情况和无耗散情况下往往随高度衰减。这种与传统的Eliassen-Palmrelation的明显矛盾仅仅与计算动量收支的域的非分区、非周期几何结构和捕获的背风波的存在有关。在这种情况下，伪动量守恒方程的空间平均表明，波在地面上的阻力等于波的伪动量通过其上下边界进入域。在被困背风波存在的情况下，通过背风边界进入的伪动量量代表了阻力的重要部分，并解释了雷诺应力和表面阻力之间的差异。在这种情况下，大尺度流动不需要在物理域内进行修正，因为进入的伪动量等于波通过域边界传递的进入动量。结果表明，当引力波耗散时，传统的重力波阻力方案通过改变低水平的大尺度动量，可以很容易地表示捕获波。DOI: 10.1034 / j.1600-0870.1998.00002.x
The linear mountain drag in the presence of trapped lee waves is calculated using a twodimensionallinear anelastic model. In many cases, it is shown that the drag is affected by thewave refraction index aloft, but remains well predicted by the drag due to hydrostatic freelypropagating mountain waves. In contrary, the vertical profile of the waves’ Reynolds stress isvery sensitive to the mean flow variation, and often decays with altitude in the steady case andin the absence of dissipation. This apparent contradiction with the conventional Eliassen-Palmrelation is simply related to the non-zonal, non-periodic geometry of the domain in which themomentum budget is calculated and to the presence of trapped lee-waves. In this context, thespatial average of the pseudo-momentum conservation equation shows that the wave drag atthe ground is equal to the wave pseudo-momentum entering in the domain through its upperand leeward boundaries. In the presence of trapped lee-waves, the amount of pseudo-momentumentering through the leeward boundary represents a significant part of the drag, and explainsthe difference between the Reynolds stress and the surface drag. In this case, the large-scaleflow does not need to be modified inside the physical domain, because the entering pseudomomentumequals the entering momentum transported by the waves across the domain boundaries.It is suggested that conventional gravity wave drag schemes can easily represent thetrapped waves by altering the large scale momentum at low level, when the waves are dissipated. DOI: 10.1034/j.1600-0870.1998.00002.x