QBO-MJO Coupling may be Mediated by the Tropopause Height Change (Invited Presentation)

6-10 January 2019, Phoenix, AZ, USA

QBO-MJO coupling may be mediated by the tropopaue height change

Seok-Woo Son¹, Yuna Lim¹

¹School of Earth and Environmental Sciences, Seoul National University, South Korea

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 slope of the cold trap, overriding the MJO-related diabatic heating, becomes smaller during EQBO winters due to the easterlies and enhanced static stability in the tropical tropopause layer. This causes a broader region of static instability. An equatorial Rossby radius of deformation also becomes larger in response to the lifted tropopause. Considering the fact that MJO in a larger horizontal scale often accompanies a stronger cloud-radiation feedback and stronger convection, these results indicate that an enhanced MJO activity during EQBO winters is likely caused by the length-scale change of MJO in response to the QBO-related tropopause change.