Study On The Zonal Variation Of Western Pacific Warm Pool

Western Pacifiic warm pool (WPWP) assembles the warmest seawaters of the open ocean in the world. The maintaining and variation of WPWP play a key role in impacting the changes of the global weather and climate. A comprehensive and systemic study on the characters, mechanism and effect on ENSO of the zonal variation of WPWP from points of oceanography view is indispensable to understand deeply the coupled process of sea and air and investigate the role of WPWP variation in ENSO cycle and global climate change, and has important theoretic, practical significance.Based on long-time series of oceanic and atmospheric data, the characteristics of the zonal displacement of whole WPWP, the oscillations of the body of WPWP warm water, and the effect of WPWP zonal variation on ENSO are investigated using EOF (Empirical Orthogonal Function), wavelet analysis methods and so on. The joint effect of western Pacific warm pool and eastern Pacific warm pool (EPWP) on ENSO is analyzed. The effect of wind and current on WPWP zonal variation is discussed. And the dynamic mechanism of the zonal variation of WPWP is diagnosed using an intermediate ocean model. The main content and results are as follows.Using weighted-average method, a good eastern edge index denoting whole WPWP zonal displacement is introduced. The interannual and interdecadal variation of WPWP zonal displacement and the diversity of zonal displacement of warm water in WPWP interior are analyzed. And the affect of the zonal displacement of WPWP on the western Pacific sea level height and the depth of thermocline, as well as the relation with ENSO, is discussed. The results show that: the zonal displacement of WPWP are of most striking interannual (2-7a) and interdecadal (10-16a) changes, and underwent a climate shift in 1976. The interior of WPWP can be divided spatially into two parts, i.e. upper and lower parts, demarcated with 50m-depth. The extent of zonal displacement in upper warm pool is much more distinct than that in lower part. The zonal displacement of WPWP is the main direct factor resulting in the fluctuations of western equatorial pacific sea leve height and thermocline depth. Furthermore, WPWP zonal migration plays a important role in the formation and development of ENSO.For farther understanding the oscillations and effect of WPWP, the depth of WPWP, tropical Pacific wind stress, sea surface height and upper-ocean heat content are analyzed using EOF modthod. The results reveal that, the main variations of WPWP are seasonal meridional"seasaw"oscillation with the axis around the equator and interannual zonal"seasaw"oscillation with the axis near 170°E. The zonal"seesaw"oscillation is the dominant mode of the interannual variability of WPWP depth anomaly field. The zonal displacement of WPWP warm water is dominant reason leading to its zonal ocsillation. The variation of sea surface height and upper-ocean heat content in the tropical Pacific have nearly same oscillatory characters on ENSO timescales: the zonal"seesaw"oscillation with the axis near 170°W and the meridional"seesaw"oscillation with the axis near 5°N. The variations of wind stress associated closely with ENSO cycle possess of zonal mode and meridional mode which present zonal wind anomalies in equatorial region and off-equatorial meridional wind anomalies, respectively. WPWP zonal oscillation responds well to wind variation by about one-month lag and also interacts remarkably with it, and results in the redistribution of mass and heat of tropical Pacific uppper-ocean, which plays a important role involved strong sea-air interaction in the formation and devlopment of ENSO cycle.The western Pacific warm pool and the eastern Pacific warm pool are two important regions of warm water in tropical Pacific Ocean. The zonal variation of WPWP and meridinal variation of EPWP are anlyzed in detail. Based on this, a new idea of the joint effect of the two warm pools on ENSO is put forward. The joint effect of the two warm pools on ENSO cycle is examined with the joint index introduced. The joint index at 1.6 suggests that a new El Ni?o event would happen. This provides a new clue to the research and predication of ENSO.Based on the analysis of data, the zonal wind stress and upper-ocean current in central equatorial Pacific ocean are two important dynamic factors resulting in WPWP zonal displacement. WPWP zonal displacement can be predicated significantly using them. Employing an intermediate ocean model, the dynamic mechanism of WPWP zonal displacement is studied by analyzing the dynamical impacts of wind forced zonal current anomalies, waves (Kelvin and Rossby waves) and its boundary reflections on WPWP zonal displacement. The model results indicate that the central equatorial Pacific zonal upper-ocean current anomalies associated with waves and forced by zonal wind anomalies, are dominant dynamic mechanism of WPWP zonal displacement. The zonal current anomalies associated with waves have leading effect by around 4 months on WPWP displacement, while the wind forced zonal current anomalies drive WPWP timely. The zonal current anomalies associated with reflected waves from the Pacific western and eastern boundaries mainly play a role in driving WPWP to retreat westward.