On the role of Rossby wave breaking in the quasi‐biennial modulation of the stratospheric polar vortex during boreal winter
On the role of Rossby wave breaking in the quasi‐biennial modulation of the stratospheric polar vortex during boreal winter
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DOI：
10.1002/qj.3775
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发表时间：
2020-04
影响因子：
8.9
通讯作者：
H. Lu;M. Hitchman;L. Gray;J. Anstey;S. Osprey
中科院分区：
文献类型：
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作者：
H. Lu;M. Hitchman;L. Gray;J. Anstey;S. Osprey
当平流层低层准两年期振荡（QBO）处于东相（eQBO）时，北方冬季平流层极地涡旋受到更多干扰，而在西风相（wQBO）期间则更加稳定。众所周知，这种所谓的“霍尔顿-谭效应”（HTE）涉及罗斯贝波（RW），但细节仍然不清楚。我们重新审视了这种热带-温带联系，试图解释其季节内变化及其与罗斯贝波破碎（RWB）的关系。使用国家环境预测中心 1979-2017 年气候预报系统的等熵坐标重新分析来评估 RWB 在波导、波平均流相互作用和 QBO 引起的经向环流背景下的相关特征。在 eQBO 期间，净温带波强迫在初冬增强，向上传播的纬向波 1（波 1）的行星尺度罗斯贝波（PRW）增加约 25%。 RWB 在平流层低层也得到增强，其特点是副热带和高纬度地区出现汇聚异常，并且在 20°N–40°N、350–650 K 之间波导增强。在冬末，RWB 导致有限幅度的增长，这阻碍了 PRW 的向上传播。纬向波数 2 和 3 (wave-2-3) 的影响最为显着。在 wQBO 期间，与波 2-3 相关的 RWB 在平流层上层增强。冲浪区的波浪吸收/混合增强了初冬至仲冬的稳定极地涡旋。平流层上层温带波导的极向限制迫使 RWB 在 1 月份左右向下延伸。随后，向上传播的波 2-3 加强，极地涡旋响应在 2 月左右从加强转变为扰动，因此冬末 HTE 出现符号反转。
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 ∼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°N–40°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.