NCEP/CFSR再分析耦合资料中MJO对ENSO的影响研究

基于1979—2008年NCEP/CFSR再分析耦合数据集,研究了冬季MJO对ENSO事件的影响。结果表明,在年际时间尺度以及长期的年代际时间尺度上,热带印度洋MJO活动的强弱性都可以影响热带中东太平洋ENSO事件的发生和发展。在年际时间尺度上,ENSO发生前期征兆的赤道中东太平洋的西风爆发事件(Westerly Wind Burst,WWB),作为MJO影响ENSO的主要途径,存在着显著的次季节时间尺度的变化。相对于气候平均的赤道太平洋西部暖池区上升而东部下沉的Walker环流,MJO正位相东传后的西风异常,减弱了低层东风和赤道东太平洋海水上翻。这一上升海流的减弱导致了中东赤道太平洋的海温升高,从而有利于ENSO暖海温事件的发生。而在年代际时间尺度上,MJO范围和强度在1998年前后出现了明显的转变,1998年之前MJO的东移范围更东,强度更强,从而导致了西太平洋西风爆发区的次季节西风异常事件更加显著,在Bjeknes正反馈机制下对应了年代际时间尺度下的强尼诺事件出现,1998年之后则与之相反。冬季MJO对ENSO影响的这一年代际特征主要体现在晚冬季节,而在早冬伴随着印度洋的增暖,MJO强度一直在逐年增加。

The influences of MJO on the ENSO based on the NCEP/CFSR reanalysis coupling data

Based on the NCEP/CFSR reanalysis coupling data, the influences of MJO on the ENSO are investigated. The results show that intensities of MJO in the tropical Indian Ocean can affect the occurrence and development of the ENSO on the interannual and interdecadal time scales. Further analyses show that,the Westerly Wind Burst (WWB) over the equatorial central eastern Pacific, as the earlier stage signal of ENSO and the main way for MJO to influence ENSO,has significant sub-seasonal variations on the interannual time scale. Compared with the Walker circulation with the warm pool area over the equatorial western Pacific with climatological mean condition rising and the eastern Pacific sinking, the abnormal westerly after the positive phase of MJO moves eastward weakens the easterly at the low level and results in the upwelling sea water in the equatorial eastern Pacific. The weakening of the upwelling leads to rising sea surface temperature of the equatorial central eastern Pacific, which creating a favorable condition for the occurrence of ENSO. However, there was an obvious change on the ranges and strength of MJO around 1998 on the interdecadal time scale. The stronger MJO moved further eastward before 1998, causing more significant and frequent WWB events in the western Pacific, which corresponds to the strong ENSO under the Bjekness positive feedback mechanism on the interdecadal time scale. The situation after 1998 is the opposite.The influences of MJO on the ENSO in winter are more obvious in late winters on the interdecadal time scale. However, in the early winters, MJO intensifies increasingly with the Indian Ocean warming.