Annual Cycle of Equatorial Zonal Circulations from the ECMWF Reanalysis

[摘要] The ECMWF 1979-93 upper-air dataset (ECM) has been evaluated for evidence of equatorial zonal circulation cells around the globe. For this it is essential not only to isolate the divergent part of the wind, but also to ascertain the continuity following the flow between the centers of upward and downward motion. The present analysis from ECM complements a recent evaluation from the NCEP-NCAR 1958-97 dataset (NCP). The searches from ECM and NCP are in overall broad agreement concerning the existence of equatorial zonal circulation cells. Over the eastern to central Pacific, a well developed cell with subsidence in the East is found all year round. In ECM this extends to the surface layer, while in NCP the westward return flow is concentrated in the mid troposphere. Both ECM and NCP yield a cell over the western Atlantic in boreal winter, characterized by subsidence in the East and divergent westward flow at the surface. In the Indian Ocean sector, both ECM and NCP capture a strong cell in boreal autumn, with subsidence over the East African coast and eastward flow in the lower troposphere. In perspective, equatorial zonal circulation cells are confined to certain seasons and longitudes over the oceans, with strong zonal flow in the lower troposphere.

[学科分类] 大气科学