Combined Effect Of The Stratospheric QBO And ENSO On The Tropical MJO

The El Ni?o-Southern Oscillation(ENSO)and stratospheric quasi-biennial oscillation(QBO)have been found to have strong impacts on Madden-Julian Oscillation(MJO)propagation.Here,we investigate the combined effect of ENSO and QBO on the MJO.Our results show that the western Pacific(WP)MJO originated from the Indian Ocean(IO)during La Ni?a/QBO easterly years is stronger than that during El Ni?o years.This relation,however,disappears during La Ni?a/QBO westerly years.The reason is that the ENSO and QBO have different effects on each MJO event.For an El Ni?o year,there is only about one MJO event,and the QBO effect is small.During a La Ni?a/QBO easterly year,there are 1.7 MJO events,while during a La Ni?a/QBO westerly year,there are only 0.6 MJO events.The El Ni?o can reinforce the MJO over the WP due to the positive moisture advection of El Ni?o mean state by MJO easterly wind anomalies.The QBO mainly affects the MJO over the Maritime Continent(MC)region by changing the high-cloud-controlled diurnal cycle;and the MC barrier effect is enhanced during QBO westerly phase due to strong diurnal cycle.During El Ni?o years,even the MJO over the MC is suppressed by the QBO westerly phase;the MJO can be reinforced over the WP.During La Ni?a/QBO westerly years,the MJO over the MC is suppressed due to strong MC diurnal cycle,and it is further suppressed over the WP due to the lack of reinforcement process.