Influence of Large-Scale 200 mb Tropical Divergence Events on the Midlatitude Zonal Flow Over the Asia-Pacific Region during the 1983-1984 Winter

摘要

Global band analysis grid point data produced by FNOC for the 1983/1984 winter season are used to study the daily variation of the midlatitude 200 mb zonal wind in relation to the divergence field. It is found that the enhancements of tropical divergence are well correlated with the intensification of the westerly jet in the midlatitudes. Three cases of the tropical divergence events were associated with tropical storm activities. This association asserts that westerly jet intensification is, in fact, a response to the tropical divergence enhancement, accepting the view that developed tropical storms are tropically-forced systems. A case of tropical divergence enhancement was also found to be attributable to a cold surge, reaffirming the importance of the cold surge related jet acceleration. Further, the study also confirms the downstream propagation of the jet streak; the existence of thermally indirect circulations at the jet exit region of the jet, both in the time-mean and in the transient motion fields.