DIAGNOSIS OF LOW FREQUENCY COMPONENT OF ENSO VARIABILITY-PART Ⅰ:GLOBAL-SCALE DYNAMIC CHARACTERISTICS OF THE COMPONENT

Composite investigation is performed of global dynamic characteristics of 3-4-year period low-frequency oscillation in ENSO variability of air-sea coupling in the context of monthly mean wind and SSTA.Evidence suggests that the horizontal(vertical) anomaly circulation at tropical latitudes (equatorial)exhibits their evolution to be,in substance,a kind of low-frequency wave slowly travelling eastward,featured by wave number 2 moving along the equator and zonal wind swiftly decaying off the equator in relation to divergence/convergence:the time that the low-frequency wave takes to move around the equator in its halfway is precisely the period of the ENSO low-frequency component (LFC) (approximately 4 years);the ocean also displays corresponding response to the component.