GLOBAL EQUATORIAL VARIABILITY OF 850 AND 200 HPA ZONAL WINDS FROM RAWINSONDES BETWEEN 1963 AND 1989

The longitude-height-time variability of 3 month averaged zonal wind a nomalies at 850 and 200 hPa over the equatorial area (5 degrees N-5 de grees S) is analyzed using a three-dimensionnal dataset constructed fr om rawinsonde data (1963-1989). The first mode, closely related to the Southern Oscillation Index, suggests a strong vertical coupling assoc iated with a horizontal out-of-phase pattern between the central/weste rn Pacific and the remainder of the equatorial belt. The vertical coup ling appears to be phase-locked to the annual cycle with Strongest int ensities found over South America and near the maritime continent earl y in the calendar year and over the Pacific basin and Africa during th e second half of the year. This mode of variability can be viewed as a standing pattern superimposed with an eastward-migrating component, c oherent with the annual cycle. This westerly moving mode originates ne ar the maritime continent during the northern autumn, and tends to pre cede E1 Nino/Southem Oscillation events in the central and eastern Pac ific Ocean. Variance is mainly concentrated in the 3-8 year low-freque ncy time scale throughout the tropics, and in the 2-3 year quasi-bienn al band from 110 degrees-120 degrees E to 180 degrees.