Revisiting the Quasi-Biennial Oscillation as Seen in ERA5. Part I: Description and Momentum Budget
Revisiting the Quasi-Biennial Oscillation as Seen in ERA5. Part I: Description and Momentum Budget
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DOI：
10.1175/jas-d-20-0248.1
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发表时间：
2020-08
影响因子：
3.1
通讯作者：
H. Pahlavan;Q. Fu;J. Wallace;G. Kiladis
中科院分区：
文献类型：
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作者：
H. Pahlavan;Q. Fu;J. Wallace;G. Kiladis
ERA 5研究了准两年振荡（QBO）的动力学和动量收支。由于ERA 5的空间分辨率更高，它能够解决更广泛的大气波的频谱，并允许更好地表示波平均流的相互作用，这两者都是至关重要的QBO研究。结果表明，QBO引起的平均纬向环流，主要局限于冬季半球，是强大的，足以中断的西风切变带下降期间的热带上升流。由于动量平流倾向于阻尼QBO，波强迫是负责向下传播和QBO的维持。结果表明，所需的波强迫的一半是由解决波在下降的西风和东风制度。行星尺度波占西风切变带下降的大部分解析波强迫，波长短于2000 km的小尺度重力波（SSG）占其余部分。SSG波解释了东风切变带下降的大部分解析强迫。在ERA 5和ERA-Interim中，QBO中平均场的表示非常相似，但ERA 5中解析的波强迫明显更强。各种赤道捕获波模式的QBO强迫的贡献记录在第二部分。
The dynamics and momentum budget of the quasi-biennial oscillation (QBO) are examined in ERA5. Because of ERA5’s higher spatial resolution compared to its predecessors, it is capable of resolving a broader spectrum of atmospheric waves and allows for a better representation of the wave–mean flow interactions, both of which are of crucial importance for QBO studies. It is shown that the QBO-induced mean meridional circulation, which is mainly confined to the winter hemisphere, is strong enough to interrupt the tropical upwelling during the descent of the westerly shear zones. Since the momentum advection tends to damp the QBO, the wave forcing is responsible for both the downward propagation and for the maintenance of the QBO. It is shown that half the required wave forcing is provided by resolved waves during the descent of both westerly and easterly regimes. Planetary-scale waves account for most of the resolved wave forcing of the descent of westerly shear zones and small-scale gravity (SSG) waves with wavelengths shorter than 2000 km account for the remainder. SSG waves account for most of the resolved forcing of the descent of the easterly shear zones. The representation of the mean fields in the QBO is very similar in ERA5 and ERA-Interim but the resolved wave forcing is substantially stronger in ERA5. The contributions of the various equatorially trapped wave modes to the QBO forcing are documented in Part II.