17:15 〜 19:15
[AAS08-P02] Global environment for equatorial cyclone Vamei: Role of the sudden stratospheric warming in December 2001
キーワード：Tropical cyclone、Sudden stratospheric warming、Deep convection、Tropical Tropopause Layer
Tropical cyclone (TCs) Vamei was generated in December 2001 over the South China Sea close to the equator where Coriolis force is small. According to Chang et al. (2003), important factor for the formation of the TC was a strong cold surge persisted for nearly one week over the narrowing South China Sea. To understand what produced such local condition, global environment is investigated in the present study.
During early December 2001, TCs were formed over the Pacific Ocean following the active region of the Madden-Julian Oscillation (MJO). The MJO stalled over the Pacific Ocean after 22 December. Thereafter, TCs are formed over wide range of longitude from the Indian Ocean to the Pacific. In particular three TCs are formed over narrow sea between lands: Vamei over the South China Sea on 26 December, Cyprien over the Mozambique Channel on 30 December, and Berni over the Gulf of Carpentaria on 31 December. It should be noted that in these regions cyclonic eddy is often formed due to geographical condition. Such cyclonic eddies are, however, shallow and it needs some other factors for eddy develops to TC.
In fact, a strong sudden stratospheric warming (SSW) occurred in late December 2001, which produced cooling over the tropical lower stratosphere. Then, very deep convections are generated in the tropics, especially over and near lands. Then, eddies coupled with deep convection became deeper. Thus, Vamei, Cyprien, and Berni, are generated over narrow region of sea between lands. This result suggests that adding to a cold surge over the South China Sea to form Borneo vortex, cooling in the tropical tropopause layer forced by the SSW, would contribute a generation of the equatorial TC Vamei by enhancing deep convection.
During early December 2001, TCs were formed over the Pacific Ocean following the active region of the Madden-Julian Oscillation (MJO). The MJO stalled over the Pacific Ocean after 22 December. Thereafter, TCs are formed over wide range of longitude from the Indian Ocean to the Pacific. In particular three TCs are formed over narrow sea between lands: Vamei over the South China Sea on 26 December, Cyprien over the Mozambique Channel on 30 December, and Berni over the Gulf of Carpentaria on 31 December. It should be noted that in these regions cyclonic eddy is often formed due to geographical condition. Such cyclonic eddies are, however, shallow and it needs some other factors for eddy develops to TC.
In fact, a strong sudden stratospheric warming (SSW) occurred in late December 2001, which produced cooling over the tropical lower stratosphere. Then, very deep convections are generated in the tropics, especially over and near lands. Then, eddies coupled with deep convection became deeper. Thus, Vamei, Cyprien, and Berni, are generated over narrow region of sea between lands. This result suggests that adding to a cold surge over the South China Sea to form Borneo vortex, cooling in the tropical tropopause layer forced by the SSW, would contribute a generation of the equatorial TC Vamei by enhancing deep convection.