What Controls the Probability Distribution of Local Wave Activity in the Midlatitudes?
What Controls the Probability Distribution of Local Wave Activity in the Midlatitudes?
复制标题
DOI：
10.1029/2020jd034501
复制
发表时间：
2021-07
期刊：
影响因子：
--
通讯作者：
C. Valva;N. Nakamura
中科院分区：
文献类型：
--
作者：
C. Valva;N. Nakamura
本文研究了局地波活动(LWA)的概率分布，以及控制它们的因素。局地波活动是衡量急流曲折的一个指标。观测到的列平均LWA分布表现出明显的季节、半球间和区域变化，但在温带外总是正偏斜的，它们的尾部经常涉及急流的中断。由观测到的瞬时涡旋强迫谱驱动的一维(1D)交通流模型定性地再现了观测到的LWA分布的形状。结果表明，即使涡旋强迫是对称分布的，LWA纬向平流中的偏斜分布也是由非线性引起的。当单独引入时，较慢的喷流和较强的瞬变和定常涡流强迫都会拓宽LWA分布，并增加自发喷流破裂的概率。准地转两层模式也模拟了上层偏斜的LWA分布。然而，在两层模式中，瞬变涡流强迫和急流速度都随着切变(经向温度梯度)的增加而增加，并且它们的相反影响使得急流破裂的频率对垂直切变不敏感。当模式的位涡纬向通量的非线性被人为抑制时，它阻碍了波流相互作用，实际上消除了上层纬向风的逆转。这项研究强调了Rossby波在纬向传播中的非线性对急流中断和相关天气异常频率的重要性。
This paper examines probability distributions of local wave activity (LWA), a measure of the jet stream's meander, and factors that control them. The observed column‐mean LWA distributions exhibit significant seasonal, interhemispheric, and regional variations but are always positively skewed in the extratropics, and their tail often involves disruptions of the jet stream. A previously derived one‐dimensional (1D) traffic flow model driven by observed spectra of transient eddy forcing qualitatively reproduces the shape of the observed LWA distribution. It is shown that the skewed distribution emerges from nonlinearity in the zonal advection of LWA even though the eddy forcing is symmetrically distributed. A slower jet and stronger transient and stationary eddy forcings, when introduced independently, all broaden the LWA distribution and increase the probability of spontaneous jet disruption. A quasigeostrophic two‐layer model also simulates skewed LWA distributions in the upper layer. However, in the two‐layer model both transient eddy forcing and the jet speed increase with an increasing shear (meridional temperature gradient), and their opposing influence leaves the frequency of jet disruptions insensitive to the vertical shear. When the model's nonlinearity in the zonal flux of potential vorticity is artificially suppressed, it hinders wave‐flow interaction and virtually eliminates reversal of the upper‐layer zonal wind. The study underscores the importance of nonlinearity in the zonal transmission of Rossby waves to the frequency of jet disruptions and associated weather anomalies.