Modulation of the mesospheric semiannual oscillation by the quasibiennial oscillation
Modulation of the mesospheric semiannual oscillation by the quasibiennial oscillation
复制标题
准两年一次振荡对中层半年振荡的调制
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
F. Sassi
中科院分区：
文献类型：
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作者：
R. Garcia;F. Sassi
最近的卫星和雷达观测表明，平流层准两年振荡（QBO）对中间层的半年振荡（SAO）有调制作用。这种调制只在SAO东风阶段才明显，当QBO风是西风时比东风时要强得多。我们使用赤道β-平面模型来演示如何通过选择性阻尼深对流激发的赤道波谱来实现这样的调制。受影响最大的波是相速低于100 - 40 m s-1的东向重力惯性波。这接近QBO东风阶段的纬向风速（−30至−35 m s−1），因此波在平流层传播时会受到强烈的热阻尼甚至吸收。由于这些波是重要的驱动模式中的中层顶SAO的东风相，该阶段是较弱的平流层QBO风是东风。由于两个原因，SAO的西风相位没有发生类似的调制：（1）QBO西风只有QBO东风的一半强，（2）SAO西风相位的大部分驱动是由相位速度为40-60 m s−1的开尔文波完成的。因此，QBO风对西风相速度的波的垂直传播的影响可以忽略不计，因此对模拟的SAO的西风相。
Recent satellite and radar observations suggest that the semiannual oscillation (SAO) in the mesosphere is modulated by the stratospheric quasibiennial oscillation (QBO). The modulation is only apparent during the SAO easterly phase, which is considerably stronger when QBO winds are westerly than when they are easterly. We use an equatorial beta-plane model to demonstrate how such a modulation could come about through selective damping of the equatorial wave spectrum excited by deep convection. The waves affected most strongly are easterly inertia-gravity waves of phase speeds slower than ∼ −40 m s−1. This is close to the zonal wind speed during the easterly phase of the QBO (−30 to −35 m s−1), so the waves suffer strong thermal damping or even absorption as they propagate through the stratosphere. Because these waves are important for driving the easterly phase of the mesopause SAO in the model, that phase is weaker when the stratospheric QBO winds are easterly. A similar modulation of the westerly phase of the SAO does not occur for two reasons: (1) QBO westerlies are only half as strong as QBO easterlies, and (2) much of the driving of the westerly phase of the SAO is accomplished by Kelvin waves of phase speed ∼40–60 m s−1. As a consequence, the QBO winds have negligible influence on the vertical propagation of waves with westerly phase velocity and hence on the westerly phase of the modeled SAO.