Short term teleconnections associated with western Pacific tropical cyclones

Abstract

The short term teleconnections arising from an individual tropical cyclone in the western Pacific were examined using a global operational data assimilation system and forecast model. In the data assimilation, the tropical cyclone was modified using a tropical cyclone bogusing procedure that either maintained the storr.' in, or eliminated the storm from, the model's initial conditions. These differant initial conditions were used as the initial fields for several 20 day runs of thfJ forecast model. These runs were used to simulate the global atmosphere with and without the tropical cyclone. The differences between these simulations were used to infer the global teleconnection response to the tropical cyclone. This response was dominated by a strong, quasi-stationary Rossby wave train that extended from east Asia across the North Pacific into North America. This wave train was initiated when an anticyclonic circulation formed near Japan as the tropical cyclone approached the east Asian jet. The anticyclone formation was primarily the result of the absolute vorticity advection by the divergent wind and vortex stretching (i.e., the Rossby wave source) associated with the tropical cyclone. The wave response continued to develop after this wave source, and the tropical cyclone itself, dissipated. This development was clearly seen in the growth and eastward propagation of Rossby wave energy across the midlatitude North Pacific and North America. The growth tended to be greater near areas of potential barotropic instability along the North Pacific jet, while the propagation tended to occur parallel to the jet. The net effect of the tropical cyclone was especially evident in the North Pacific - North American region, where the model atmosphere with the tropical cyclone showed a midlalitude jet and storm track that were markedly different from the jet and storm track seen in the model atmosphere without the tropical cyclone. The two tropical cyclones investigated in this study were super typhoon Yuri (November-December 1991) and typhoon Robyn (August 1993).