Global equatorial variability of 850 and 200 hPa zonal winds from rawinsondes between 1963 and 1989

Abstract

The longitude‐height‐time variability of 3‐month averaged zonal wind anomalies at 850 and 200 hPa over the equatorial area (5°N‐5°S) is analyzed using a three‐dimensionnal dataset constructed from rawinsonde data (1963–1989). The first mode, closely related to the Southern Oscillation Index, suggests a strong vertical coupling associated with a horizontal out‐of‐phase pattern between the central/western Pacific and the remainder of the equatorial belt. The vertical coupling appears to be phase‐locked to the annual cycle with strongest intensities found over South America and near the maritime continent early in the calendar year and over the Pacific basin and Africa during the second half of the year. This mode of variability can be viewed as a standing pattern superimposed with an eastward‐migrating component, coherent with the annual cycle. This westerly moving mode originates near the maritime continent during the northern autumn, and tends to precede El Nino/Southern Oscillation events in the central and eastern Pacific Ocean. Variance is mainly concentrated in the 3–8 year low‐frequency time scale throughout the tropics, and in the 2–3 year quasi‐biennal band from 110°–120°E to 180°.