热带平流层大气的准两年振荡（Quasi-biennial oscillation，简称QBO），表现为东西风的周期性转变，平均周期约28-29个月。波动沿赤道对称分布，动力成因是罗斯贝波和开尔文波在高空的循环下传。

QBO的定义层面在30hPa，东西风向的转换信号向下传播到70hPa层通常需要6个月，传播至100hPa层面时风向信号已不明显。由于平流层和对流层的质量密度的悬殊，QBO的波动能量还不足以显着改变对流层顶的流场。QBO通常通过对沃克环流的调整影响对流层环流，例如QBO东风位相年利于厄尔尼诺事件的发生。

The quasi-biennial oscillation (QBO) is a quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found.