Annual cycle of equatorial east-west circulation over the Indian and Pacific Oceans

Abstract

The present study provides evidence that the midlatitude-equatorial coupling is primarily responsible for the maintenance of the annual mean total 200-mb zonal winds along the equator, whereas convection contributes a great deal to the annual mean upper-level equatorial divergent winds. The annual cycles differ remarkably between the equatorial Indian and eastern Pacific oceans. The annual cycle in the equatorial Indian Ocean is characterized by: 1) the eastward phase propagation of monthly mean anomaly zonal winds with an inverse relationship between the surface and 200 mb (i.e., baroclinic structure in the vertical), and 2) the highest SST occurring about three (four) months prior to the strongest surface westerlies (minimum OLR). The annual cycle in the equatorial eastern Pacific exhibits coherent westward propagation of monthly mean anomaly SST and surface zonal winds, indicating the importance of planetary boundary-layer processes. -from Authors