Abstract
The 200-mb tropical wind fields analyzed at Florida State University for 1965–74 and the 200 and 700 mb tropical wind fields from the National Meteorological Center for 1979–82 were used to explore the mechanism for the interannual variation of the tropical easterly jet. This jet is generally weaker during the summers of Warm Events (dry summers) in the Southern Oscillation when anomalously warm surface water appears over the eastern and central equatorial Pacific and drought occurs over the Indian subcontinent. It is observed that divergence (convergence) exists on the upstream (downstream) side of the jet. The tropical divergent circulations, i.e., the east-west Walker and the local Hadley circulations, during such summers are weakened and shifted eastward. Therefore, divergence anomalies appear in the upper troposphere over equatorial Africa or the cast coast of Africa, whole convergence anomalies exist over the Indian subcontinent or the Arabian Sea. These changes of the tropical divergent circulations may cause the change in the energetics maintenance of the tropical easterly jet. Our analysis shows that the divergence anomalies of the divergent kinetic energy flux appear over the east coast of Africa, and the convergence anomalies of divergent kinetic energy flux appear over the Indian subcontinent. It is inferred from these anomalies of kinetic energy flux that the kinetic energy generation and destruction associated with the tropical easterly jet are less in dry summers.
Based upon these changes in the upper-level tropical circulations during dry summers, a suggestion is altered that relates the anomalously warm surface water over the eastern and central equatorial Pacific to the weakening of the low-level monsoon circulation and the tropical easterly jet.
