Interactions between Mesoscale and Submesoscale Gravity Waves and Their Efficient Representation in Mesoscale-Resolving Models
Interactions between Mesoscale and Submesoscale Gravity Waves and Their Efficient Representation in Mesoscale-Resolving Models
复制标题
介尺度和次介尺度重力波之间的相互作用及其在介尺度解析模型中的有效表示
DOI：
10.1175/jas-d-17-0289.1
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发表时间：
2018
影响因子：
3.1
通讯作者：
U. Achatz
中科院分区：
文献类型：
--
作者：
J. Wilhelm;T. Akylas;G. Bölöni;Junhong Wei;B. Ribstein;R. Klein;U. Achatz
由于目前的天气预报规范和越来越多的大气气候模型至少解析了部分中尺度流，因此也解析了内部重力波（GW），因此很自然地要问，即使在这种配置中，亚网格尺度的GW是否也可能影响解析的流，以及如何考虑它们的影响。这激发了对未解析的亚介尺度和解析的介尺度引力波之间相互作用的理论和数值研究，为简单起见，使用布辛涅斯克动力学。通过标度参数，首先确定了确实可以影响中尺度引力波动力学的亚中尺度引力波子集。其中，波长对应于当今有限区域天气预报模型的最大未解析尺度的静水引力波是一个有趣的例子。然后，基于利用适当尺度分离参数的多尺度渐近分析，制定了允许中尺度不平衡流动的大幅 WKB 理论。亚介尺度引力波的纯垂直传播被发现是最重要的，这意味着解析流仅受前序次介尺度水平动量的垂直通量收敛的影响。反过来，亚中尺度引力波被中尺度垂直风切变折射，同时保持其波浪作用密度。该理论的有效数值实现使用相空间射线追踪器，从而处理频繁出现的焦散。 WKB 方法及其数值实现已通过水平和垂直限制的亚介尺度引力波包对中尺度惯性引力波的共振辐射的亚介尺度解析模拟进行了成功验证。
As present weather forecast codes and increasingly many atmospheric climate models resolve at least part of the mesoscale flow, and hence also internal gravity waves (GWs), it is natural to ask whether even in such configurations subgrid-scale GWs might impact the resolved flow and how their effect could be taken into account. This motivates a theoretical and numerical investigation of the interactions between unresolved submesoscale and resolved mesoscale GWs, using Boussinesq dynamics for simplicity. By scaling arguments, first a subset of submesoscale GWs that can indeed influence the dynamics of mesoscale GWs is identified. Therein, hydrostatic GWs with wavelengths corresponding to the largest unresolved scales of present-day limited-area weather forecast models are an interesting example. A large-amplitude WKB theory, allowing for a mesoscale unbalanced flow, is then formulated, based on multiscale asymptotic analysis utilizing a proper scale-separation parameter. Purely vertical propagation of submesoscale GWs is found to be most important, implying inter alia that the resolved flow is only affected by the vertical flux convergence of submesoscale horizontal momentum at leading order. In turn, submesoscale GWs are refracted by mesoscale vertical wind shear while conserving their wave-action density. An efficient numerical implementation of the theory uses a phase-space ray tracer, thus handling the frequent appearance of caustics. The WKB approach and its numerical implementation are validated successfully against submesoscale-resolving simulations of the resonant radiation of mesoscale inertia GWs by a horizontally as well as vertically confined submesoscale GW packet.