The role of tropical tropopause in QBO-MJO coupling (#1044)
The boreal-winter Madden-Julian Oscillation (MJO) convections are better organized and propagate farther eastward during the easterly phase of Quasi-Biennial Oscillation (EQBO). Here we suggest that such a modulation of MJO is caused by the QBO-related mean state and tropopause height changes. The lower stratospheric cold trap, overriding the MJO-related diabatic heating, becomes colder during EQBO winters. This causes a weaker static stability, strengthening the MJO convection. In addition, the slope of the cold trap becomes smaller during EQBO winters, inducing a broader region of static instability. Considering the fact that MJO in a larger horizontal scale often accompanies a stronger cloud-radiation feedback and stronger convection, an enhanced MJO activity during EQBO winters is also likely caused by the length-scale change of MJO in response to the QBO-related tropopause change.