The Influences of Zonal Flow on Wave Breaking and Tropical-Extratropical Interaction in the Lower Stratosphere

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Abstract
The influences of the zonal-mean flow on Rossby wave breaking and tropical-extratropical interaction in the lower stratosphere are investigated using a high-resolution barotropic model. It is found that the zonal-mean wind in the subtropics of the winter hemisphere, denoted as ū30°, is pivotal to the location and intensity of Rossby wave breaking. When ū30° is positive and relatively large, significant wave breaking occurs in two regions: one in the midlatitudes of the winter hemisphere and the other in the Tropics. When ū30° is small or negative, on the other hand, wave breaking occurs primarily in the middle-to-high latitudes of the winter hemisphere. It is also found that when ū30° is large, wave breaking is sensitive to the phase of the equatorial quasi-biennial oscillation (QBO) in that if the QBO is westerly, significant wave breaking takes place in the midlatitudes of the winter hemisphere and the subtropics of the summer hemisphere and no wave breaking occurs in the equatorial region, and if the QBO is easterly, significant wave breaking occurs only in the winter hemisphere. When ū30° is small or negative, wave breaking is insensitive to the phase of the QBO.

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