Stratospheric Control of Organized Tropical Deep Convection during Boreal Winter

Interannual variation of seasonal-mean tropical convection, especially that over the Indo-Pacific region, is primarily controlled by the El Niño-Southern Oscillation (ENSO). For example, during El Niño winter, large-scale convection over the Maritime Continent becomes weaker than normal, while that over the central to eastern Pacific is strengthened. Here, we show that such a regulation by the ENSO does not hold for subseasonal convective activity that is associated with the Madden-Julian Oscillation (MJO). The boreal-winter MJO is instead closely linked with the stratospheric Quasi-Biennial Oscillation (QBO). The QBO-related MJO change, typically stronger and more organized MJO when 50-hPa zonal wind at the equator is easterly, explains up to 40% of interannual variation of MJO amplitude. This result suggests that the organized tropical deep convection and the related tropical-extratropical teleconnections can be better understood and predicted by taking stratospheric mean state into account.