Differences Of Tropic Intraseasonal Oscillation Between The Two Types Of El Ni(?)o

By using daily Outgoing Long Wave Radiation (OLR).Real-time Multivariate Madden-Julian Oscillation (RMM) and ERA-Interim reanalysis dataset for the period of 1979-2012, the influences of different types of Pacific warming, often classified as the eastern Pacific (EP) and central Pacific (CP) El Ni(?)o events, on Madden-Julian oscillation (MJO) activity over the Maritime Continent and the equatorial Indian Ocean were investigated. The main results are as follows:(1) It is found that the intensified western Pacific MJOs show a higher frequency of occurrence and a longer duration during CP El Ni(?)o events,compared to those during EP El Ni(?)o events. The diagonsis of the MJO kinetic energy budget equation indicates that the intensified convergence and cyclonic shear of large-scale background fields over the Maritime Continent contribute positively to the kinetic energy conversion from mean flow to the MJO, inducing increased MJO kinetic energy. To further examine the relative roles of thermodynamic (i.e., moisture) and dynamic (i.e., vertical wind shear) in MJO perturbations, a series of sensitivity experiments was conducted using a 2.5-layer model. The results show that both the abundant low-level moisture and stronger vertical wind shear in the western Pacific are key factors that lead to the increase of MJO intensity during CP El Ni(?)o events.(2) For the MJO over the equatorial Indian Ocean, an enhanced initiation and propagation signals of MJO were observed during the CP El Ni(?)o events.Accompanied by relatively unstable (stable) atmospheric stratification induced by enhanced (reduced) moisture and moist static energy (MSE) in the lower troposphere,strengthened (weakened) MJO convection was observed in the initiation and eastward propagation stages in the equatorial Indian Ocean during CP (EP) El Ni(?)o events. To examine the key processes resulting in the differences in low-level moistening and column MSE anomalies over the Indian Ocean associated with the two types of El Ni(?)o, the moisture and column MSE budget equations were diagnosed . The results indicate that the enhanced horizontal advection in the CP El Ni(?)o years plays an important role in causing a larger moisture/MSE growth rate over the MJO initiation area during CP El Ni(?)o events than during EP El Ni(?)o events.The increases in horizontal moisture/MSE advection primarily result from advection by mean flow across the enhanced intraseasonal moisture/MSE gradient, as well as by intraseasonal circulation across the mean moisture/MSE gradient associated with the CP El Ni(?)o. In the eastward development stage, the enhanced preconditioning comes from positive moisture/MSE advection anomalies in the CP El Ni(?)o events.Meanwhile, the strengthened MJO-related convection over the central-eastern Indian Ocean is maintained by increased atmospheric radiative heating and surface latent heat flux during the CP El Ni(?)o compared to the EP El Ni(?)o events.