Study About The Relation Between The Tropical Western Pacific Intraseasonal Oscillation And El Ninos

MJO's influence on El Ninos is studied in this paper. Our study covers the variability of MJO's vertical structure, energy and their influence on El Nino events by related Kelvin waves. The latter is the research focus of this paper.NCEP wind data is used to analyze the vertical structure of MJO by comparing the intraseasonal wind divergence on the isobaric surface of 200hpa and 850hpa. There is no barotropic structure as someone mentioned but exists a baroclinic structure all the time.Bandpass filtered NCEP OLR data is regarded as a MJO's index, which was used to analyze changes of MJO's energy during the El Nino events. The tropical west Pacific MJO's energy always boosts up before El Nino happens, and they have positive relationship. The MJO's energy recedes after the El Nino, and it keeps minus abnormal state. The positive relationships between MJO's energy and SST anomaly have been indicated by the result of SVD analysis.Correlation analysis between the zonal wind and SODA SST showed the maximum correlation coefficient when there is 6 months lag between the Tropical Western Pacific west wind and the Tropical Eastern Pacific SST, indicating that MJO plays an important role to El Nino, because MJO-related west wind is an important component of west wind. MJO's influence on El Ninos by MJO-related wind forced Kelvin waves is mainly studied. The NCEP wind data and SODA temperature and salinity data are analyzed to do that. Bandpass filtering method was used to separate the MJO-related signal, and then the relative parameters of the ocean Kelvin wave was calculated. The depth of isopycnal of 25.5kg·m-3 is used to indicate the depth of main thermocline. To analyze the influence of MJO-related Kelvin waves on El Nino, the relationship between the depth of main thermocline and the parameters of MJO-related Kelvin wave have been discussed.When MJO breaks out, the MJO-related wind stress will create the eastward Equatorial oceanic Kelvin wave with abnormal signals of the thermocline depth. The Kelvin wave plays a very important role on the process of MJO's working on El Nino. Our study shows that when the intensity of MJO-related Kelvin wave is stronger, the effect to the spreading of the thermocline signals is more effective. The MJO-related abnormal thermocline signals contain abnormal sinking and rising signals. The MJO-related sinking signals will enhance the intensity of El Nino, but MJO-related upwelling signals will weaken the intensity of El Nino. In addition, the background ocean and other disturbance signals also play important roles on the El Nino. In a word, MJO just has some influence on the El Nino, but it is not the key factor.