Combined effect of the QBO and ENSO on the MJO

本文研究了平流层准两年振荡与ENSO对MJO的协同作用。结果显示:在拉尼娜/准两年振荡东风位相,起源于印度洋到达西太平洋的MJO要比在厄尔尼诺年强。但是在拉尼娜/准两年振荡西风位相,这种关系不复存在。原因在于ENSO和准两年振荡对MJO事件的影响不同。厄尔尼诺年西太平洋地区正水汽平流有利于MJO加强,而准两年振荡西风位相下海洋性大陆地区较强的日循环会使得海洋性大陆屏障作用增强。在厄尔尼诺年,尽管MJO在准两年振荡西风位相下会受到抑制,但是在到达西太平洋是都能得到加强。在拉尼娜/准双周振荡的西风位相下,海洋性大陆较强日循环和西太平洋不利的背景条件都会抑制MJO。

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