With the use of data from the National Centers for Environmental Prediction Climate Forecast System Reanalysis,the environment and structure of typhoon Toraji(2001)are investigated during the re-intensification(RI)sta...With the use of data from the National Centers for Environmental Prediction Climate Forecast System Reanalysis,the environment and structure of typhoon Toraji(2001)are investigated during the re-intensification(RI)stage of its extratropical transition(ET),a process in which a tropical cyclone transforms into an extratropical or mid-latitude cyclone.The results provide detailed insight into the ET system and identify the specific features of the system,including wind field,a cold and dry intrusion,and a frontal structure in the RI stage.The irrotational wind provides the values of upper-and lower-level jets within the transitioning tropical cyclone and the cyclone over Shandong Peninsula,accompanied with the reduced radius of maximum surface winds around the cyclone center in the lower troposphere.Simultaneously,dry air intrusion enhances the formation of fronts and leads to strong potential instability in the southwest and northeast quadrants.The distribution of frontogenesis shows that the tilting term associated with vertical motion dominates the positive frontogenesis surrounding the cyclone center,especially in the RI stage.The diagnostics of the kinetic energy budget suggest that the divergent kinetic energy generation whose time evolution corresponds well to that of cyclone center pressure is the primary factor for the development of Toraji in the lower troposphere.The ET of Toraji is a compound pattern that contains a development similar to that of a B-type extratropical cyclone within the maintaining phase and an A-type extratropical cyclone within the strengthening period,which corresponds to the distribution of the E-P fluxes with vertically downward propagation in the maintaining stage and upwards momentum in the strengthening phase.展开更多
In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size...In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.展开更多
基金supported by the National Natural Science Foundation of China (No. 41130859)the Science Fund for Creative Research Groups (No. 41221063)
文摘With the use of data from the National Centers for Environmental Prediction Climate Forecast System Reanalysis,the environment and structure of typhoon Toraji(2001)are investigated during the re-intensification(RI)stage of its extratropical transition(ET),a process in which a tropical cyclone transforms into an extratropical or mid-latitude cyclone.The results provide detailed insight into the ET system and identify the specific features of the system,including wind field,a cold and dry intrusion,and a frontal structure in the RI stage.The irrotational wind provides the values of upper-and lower-level jets within the transitioning tropical cyclone and the cyclone over Shandong Peninsula,accompanied with the reduced radius of maximum surface winds around the cyclone center in the lower troposphere.Simultaneously,dry air intrusion enhances the formation of fronts and leads to strong potential instability in the southwest and northeast quadrants.The distribution of frontogenesis shows that the tilting term associated with vertical motion dominates the positive frontogenesis surrounding the cyclone center,especially in the RI stage.The diagnostics of the kinetic energy budget suggest that the divergent kinetic energy generation whose time evolution corresponds well to that of cyclone center pressure is the primary factor for the development of Toraji in the lower troposphere.The ET of Toraji is a compound pattern that contains a development similar to that of a B-type extratropical cyclone within the maintaining phase and an A-type extratropical cyclone within the strengthening period,which corresponds to the distribution of the E-P fluxes with vertically downward propagation in the maintaining stage and upwards momentum in the strengthening phase.
基金supported by the National Natural Science Foundation of China(Nos.40876004,40890155 and 40675060)National 973 Project(Nos.2009CB-421500 and 2007CB411801)
文摘In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.
