Year-To-Year Variability in the Hadley and Walker Circulations from NCEP/NCAR Reanalysis Data

Abstract

The year-to-year variability in the local Hadley and Walker circulations is studied by empirical orthogonal function (EOF) analysis of zonal and meridional divergent winds at 200 and 850 hPa in the NCEP/NCAR reanalysis data. The first mode of the EOF analysis for the period since 1979 is closely related to the El Nino/Southern Oscillation (ENSO). The corresponding vertical velocity structure at the middle of the troposphere is characterized by the combination of a horseshoe pattern in the western tropical Pacific and an oval pattern in the central-eastern equatorial Pacific, consistent with satellite-derived precipitation correlations. A streamline analysis for horizontal divergent winds and vertical winds revealed that the dominant local Hadley and Walker circulation anomalies connect the oval and the horseshoe, while the other clusters of the local Hadley circulation anomalies rotating in opposing directions emanate from the Maritime Continent region.