On the Role of Rossby Wave Breaking in the Quasi‐Biennial Modulation of the Stratospheric Polar Vortex during Boreal Winter
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY(2020)
摘要
The boreal-winter stratospheric polar vortex is more disturbed when the quasi-biennial oscillation (QBO) in the lower stratosphere is in its easterly phase (eQBO), and more stable during the westerly phase (wQBO). This so-called "Holton-Tan effect" (HTE) is known to involve Rossby waves (RWs) but the details remain obscure. This tropical-extratropical connection is re-examined in an attempt to explain its intraseasonal variation and its relation to Rossby wave breaking (RWB). Reanalyses in isentropic coordinates from the National Centers for Environmental Prediction Climate Forecast System for the 1979-2017 period are used to evaluate the relevant features of RWB in the context of waveguide, wave-mean-flow interaction, and the QBO-induced meridional circulation. During eQBO, the net extratropical wave forcing is enhanced in early winter with similar to 25% increase in upward propagating planetary-scale Rossby waves (PRWs) of zonal wave-number 1 (wave-1). RWB is also enhanced in the lower stratosphere, characterized by convergent anomalies in the subtropics and at high latitudes and strengthened waveguide in between at 20 degrees N-40 degrees N, 350-650 K. In late winter, RWB leads to finite amplitude growth, which hinders upward propagating PRWs. The effect is most significant for zonal wave-numbers 2 and 3 (wave-2-3). During wQBO, RWB in association with wave-2-3 is enhanced in the upper stratosphere. Wave absorption/mixing in the surf zone reinforces a stable polar vortex in early to middle winter. A poleward confinement of the extratropical waveguide in the upper stratosphere forces RWB to extend downward around January. A strengthening of upward propagating wave-2-3 follows and the polar-vortex response switches from reinforcement to disturbance around February, thus a sign reversal of the HTE in late winter. Key Findings center dot Rossby wave breaking (RWB) is enhanced in the height regions where the zero-wind line is shifted into the winter hemisphere and where the QBO-induced meridional circulation is directed toward the winter pole center dot Polar vortex responses differ in terms of the height location of RWB, zonal wave-number-dependent disturbances and seasonal development center dot Significant increase in wave-1 occurs when the QBO is in its easterly phase center dot A cumulative effect of RWB results in enhanced wave forcing of zonal wave-numbers 2 and 3 during westerly QBO, which manifests in a sign reversal of the Holton-Tan effect in late winter.
更多查看译文
关键词
Holton-Tan effect,Quasi-Biennial Oscillation,Rossby wave breaking,stratospheric polar vortex
AI 理解论文
溯源树
样例
![](https://originalfileserver.aminer.cn/sys/aminer/pubs/mrt_preview.jpeg)
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要