Annual cycle of equatorial East-West circulation over the Indian and Pacific oceans
- Univ. of Hawaii, Honolulu (United States)
Along the equator, the easterlies are strongest above the convective center over the maritime continent, while westerlies reach their maximum just above the dry zone over the equatorial Pacific. This is different from what is anticipated. 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. Annual cycles occurring over the extratropics act as a transient eddy forcing of the equatorial annual mean 200-mb zonal wind through three-dimensional convergence of localized Eliassen-Palm (E-P) fluxes and accelerate the 200-mb annual mean westerlies (easterlies) over the equatorial Indian Ocean where E-P fluxes are horizontally divergent (convergent). The baroclinic contribution appears to be minimal. 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 and (2) the highest SST occurring about three (four) months prior to the strongest surface westerlies. 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. The equatorial convection apparently contributes little to the annual cycle of the upper-level east-west equatorial circulation. The annual cycle in the upper-level zonal winds over the equatorial eastern Pacific is largely controlled by a pronounced annual cycle of the 200-mb zonal wind occurring in the extratropics of each hemisphere. 45 refs., 9 figs.
- OSTI ID:
- 6453544
- Journal Information:
- Journal of Climate; (United States), Vol. 6:5; ISSN 0894-8755
- Country of Publication:
- United States
- Language:
- English
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