Equatorial Zonal Circulations from the NCEP-NCAR Reanalysis

Abstract

The NCEP-NCAR 1958-97 upper-air dataset 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. Over the eastern to central Pacific a well developed cell persists all year round, with subsidence in the East, but with the compensating divergent westward flow concentrated in the realm of a midtropospheric jet rather than at the surface. A cell over the western Atlantic in January is characterized by subsidence in the East and divergent westerly flow at the surface. In the Indian Ocean sector during July, a small cell is recognized over the western part of the basin, contained in the upper-to mid-troposphere and with subsidence over the East African coast. In October a well developed cell spans the entire basin, with subsidence over the East African coast and eastward flow in the lower tropophere.