RECENT CHANGES IN TROPOSPHERIC CIRCULATION OVER THE CENTRAL EQUATORIAL PACIFIC

During the past five years an unusually prolonged warm event has occur red in the equatorial Pacific ocean. As recently discussed by Trenbert h and Hear [1996], this prolonged warm event represents a major climat e perturbation in the historical record of the Southern Oscillation. T he region most affected by the warm event is the central equatorial Pa cific. Upper air observations from this region are sparse. However, si nce 1986 observations of tropospheric winds have been nearly continuou sly using the made Christmas Island VHF wind profiler, These profiler observations are examined for evidence of a deep tropospheric change i n circulation during the past five years by comparing observations for 1990-1995 with those taken before 1990. It is shown that there has be en a substantial decrease in the magnitude of tropospheric zonal winds observed at Christmas Island. At the same time, the magnitude of the pressure difference between Tahiti and Darwin has also been substantia lly reduced. These observations are consistent with a warm event in wh ich the centers of active over the western Pacific have moved eastward toward the dateline. We conclude that there has been a reduction in t he tropospheric zonal winds over the central equatorial Pacific that a re normally associated with the gradients of surface pressure and SST across this region.