Waveguidability of idealized midlatitude jets and the limitations of ray tracing theory
Waveguidability of idealized midlatitude jets and the limitations of ray tracing theory
复制标题
理想化中纬度急流的波导性和射线追踪理论的局限性
DOI：
10.5194/wcd-2020-3
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发表时间：
2020
影响因子：
--
通讯作者：
V. Wirth
中科院分区：
文献类型：
--
作者：
V. Wirth
抽象。从中纬度地区源发出的定常Rossby波的射线路径通常是向赤道方向折射的。然而，这种向赤道传播的一般趋势被作为纬向波导的中纬度急流的存在所缓解。这开启了环全球遥相关和准共振的可能性，这表明在纬向方向引导波的能力是一个重要的喷流属性。本文在一个球面正压模式中研究了理想中纬度急流的波导性。一个强迫耗散模型配置与本地源Rossby波是用来量化波导通过诊断的纬度分布的波度在一个纵向部门远下游的强迫。系统的灵敏度实验表明，波导性随射流振幅的增大和射流宽度的减小而增大。这一结果与两个理想化理论概念的预测结果进行了对比，这两个理想化理论概念的基础是（1）从WKB理论导出的射线追踪和（2）具有纬向位涡锋的尖锐喷流。两个所谓的转向纬度的存在，这是根据射线追踪理论的带状波导的关键诊断，原来是一个穷人的预测依赖于射流振幅和射流宽度的数值模拟中得到的波导。相比之下，位涡的纬向梯度与诊断的波导性相关得相当好。光线跟踪的预测结果不佳并不令人惊讶，因为在当前环境下，根本的WKB假设并不满足。WKB的失败追溯到基本方程的属性，并提出了一个启发式的论点，阐明潜在的位涡（PV）梯度作为代理波导。
Abstract. Ray paths of stationary Rossby waves emanating from a local midlatitude source are usually refracted equatorward. However, this general tendency for equatorward propagation is mitigated by the presence of a midlatitude jet that acts as a zonal waveguide. This opens up the possibility of circum-global teleconnections and quasi-resonance, which suggests that the ability to guide a wave in the zonal direction is an important jet property. This paper investigates waveguidability of idealized midlatitude jets in a barotropic model on the sphere. A forced-dissipative model configuration with a local source for Rossby waves is used in order to quantify waveguidability by diagnosing the latitudinal distribution of waviness in a longitudinal sector far downstream of the forcing. Systematic sensitivity experiments show that waveguidability increases smoothly with increasing jet amplitude and with decreasing jet width. This result is contrasted with the predictions from two idealized theoretical concepts based on (1) ray tracing as derived from Wentzel–Kramers–Brillouin (WKB) theory and (2) a sharp jet with a zonally oriented front of potential vorticity. The existence of two so-called turning latitudes, which is the key diagnostic for a zonal waveguide according to ray tracing theory, turns out to be a poor predictor for the dependence of waveguidability on jet amplitude and jet width obtained in the numerical simulations. By contrast, the meridional gradient of potential vorticity correlates fairly well with the diagnosed waveguidability. The poor predictions from ray tracing are not surprising, because the underlying WKB assumptions are not satisfied in the current context. The failure of WKB is traced back to the properties of the underlying equations, and a heuristic argument is presented to elucidate the potential of the potential vorticity (PV) gradient to act as a proxy for waveguidability.
DOI：
10.1073/pnas.1412797111
发表时间：
2014-08-26
影响因子：
11.1
作者：
Coumou, Dim;Petoukhov, Vladimir;Schellnhuber, Hans Joachim
通讯作者：
Schellnhuber, Hans Joachim
影响因子：
13.6
作者：
Stadtherr L;Coumou D;Petoukhov V;Petri S;Rahmstorf S
通讯作者：
Rahmstorf S