Activity Characteristics And Influences Of MJO And Their Relationships With ENSO

Based on the NCEP reanalysis data and outputs of CMIP5 models,this article analyzed the following issues: the intensity and propagation characteristics of MJO activity over the Pacific in boreal winter and summer;the interaction between MJO and ENSO,as well as MJO and two types of ENSO;the impacts of MJO on the PacificJapan teleconnection pattern;and the modulations of ENSO on the influences of MJO on precipitation over China in boreal winter.The main conclusions are as following:The interannual and interdecadal variations of MJO over the Pacific are closely related to the intensity and duration time of strong discrete MJO events over there.MJO activity is mainly located to the west of 160°E in summer,but it is also very active over the equatorial central Pacific in winter.MJO activity over western and central Pacific in winter shows significantly different features.Accompanying the interannual variation of MJO intensity,the anomalous circulation related to MJO and the zonal propagation of MJO also show different features.There are main three types of MJO zonal propagation:the significant eastward propagation from Indian Ocean to 150°W,the significant eastward propagation from Indian Ocean to the west of 160°E,and the eastward propagation from Indian Ocean to 140°E and a westward propagation over 150°E-150°W at the same time.The relationships between MJO and ENSO vary with the regions in the troposphere.The variation of MJO kinetic energy and available potential energy show different characteristics in different regions,which is induced by different physical process.The anomalous activity of MJO over the western Pacific in spring and early summer could promote the development of ENSO event,whereas the ENSO has prominent impacts on the MJO activity over the western Pacific in winter and decaying summer.The asymmetry of MJO activity is important to promoting the development of ENSO.During the developing stage of El Ni?o,the intensity of MJO westerly and negative MJO OLR is stronger,and can propagate more east than those during the developing stage of La Ni?a.The anomalous circulation related to the ENSO sea surface temperature anomalies can impact the activity of MJO over the western Pacific,and the anomalous activity of MJO could promote the development of ENSO,therefore,there is a positive feedback process between MJO and ENSO.ENSO event could influence the zonal and meridional advections of moisture by modulating the zonal and meridional gradients of moisture,which leads to the stronger intensity of MJO activity and further east propagation during the El Ni?o winter than those during La Ni?a winter.MJO activity over the western Pacific is much weaker in eastern Pacific(EP)El Ni?o due to the stronger anomalous descending motions.Furthermore,the MJO propagates more continuously and farther eastward duringcentral Pacific(CP)El Ni?o because of robust moisture convergence over the central Pacific,which provides adequate moisture for the development of MJO convection.MJO activity is strengthened over the western Pacific during the predeveloping and developing stages of EP El Ni?o,but suppressed during the mature and decaying stages.In contrast,MJO activity do not show a clear relationship with CP El Ni?o before their occurrence over the western Pacific,but it increases over the central Pacific during the mature and decaying stages of CP El Ni?oThe activity of MJO zonal wind at low-level troposphere and MJO OLR over the western Pacific is strengthened(weakened)during the El Ni?o(La Ni?a)decaying summer.The northward propagation of MJO over the western Pacific can reach into30°N during the La Ni?a decaying summer,whereas it is confined to the south of 15°N during the El Ni?o decaying summer.On the one hand,the anomalous divergence(convergence)and suppressed(enhanced)convection induced by El Ni?o(La Ni?a)over western Pacific during decaying summer are unfavorable(favorable)to the activity of MJO;on the other hand,the combination of anomalous background circulation induced by El Ni?o(La Ni?a)and MJO anomalous circulation suppresses(promotes)the northward propagation of MJO.The multi-model ensemble of CMIP5 and AMIP models can reproduce the climatologic characteristics of MJO activity in winter and summer.However,there is obviously inadequate in simulating the propagation of MJO,especially for the northward propagation of MJO.The performances of CMIP5 models in simulating the eastward propagation of MJO are better than those in AMIP models,which indicates that the air-sea interaction is important to the simulation of MJO propagation.CMIP5 models can not reproduce the relationship between MJO and ENSO,as well as the MJO and two types of ENSO,as that in observations,and only some features are captured by a few models.The performances of AMIP models in simulating the relationship of MJO with ENSO and two types of ENSO are better than those in CMIP5 models,which indicates that the correct simulation of atmospheric circulations and oceanic conditions is important to the simulation of relationships between MJO and ENSO.The PJ and MJO over the western Pacific are closely related on interannual time-scales.As the background circulation,MJO activity has significant influences on PJ activity.The anomalous circulation related to MJO activity can impact the PJ activity directly,and the MJO also influences the PJ activity by modulating the energy transportation and transition.The intensity,spatial structure and evolution characteristics of PJ show different features during the anomalous MJO activity summer.The anomalous circulation and moisture transportation induced by MJO differ prominently in El Ni?o,La Ni?a and two types of El Ni?o winter,which leads to the different precipitation anomalies over China.The anomalous precipitation induced byMJO shows different features in El Ni?o,La Ni?a and two types of El Ni?o winter.Such as,during the 6 and 7 phases of MJO,the precipitation is enhanced(weakened)over southern(northern)parts of eastern China in El Ni?o winter,whereas it is show consistent weakening over eastern China in La Ni?a winter.