Tropical-Extratropical Interactions: The SPCZ (Invited Presentation)

The ECMWF Re-Analyses (ERA) for the 15-year period, 1979-1994, are used to create a climatology of some of the main features of the SPCZ. Among the variables examined are low level and upper level winds, including stream function and velocity potential, mid-tropospheric vertical motions, divergence and vorticity at one or more levels, precipitable water, and low level moisture convergence. In addition, OLR and SSTs are examined for the same 15-year period. Seasonal means are computed for each variable and their fluctuations during ENSO events are investigated. There were four El Ninos and two La Ninas in the period. It is planned to show the structure of the SPCZ through a variety of maps, cross-sections, vertical profiles and time series. In this context, the presentation provides an update of some of the results given in the review paper by the author in 1994. Finally, if time permits, the variation of SST gradients, a suspected cause of changes in the location of the SPCZ, will also be examined.