热带气旋“尤特”（2006）南海突然减弱的机理分析

应用NCEP/NCAR再分析资料，对热带气旋“尤特”（2006）在我国南海突然减弱的机理进行了分析。结果表明：水汽通道的切断是热带气旋“尤特”突然减弱的必要条件，“尤特”突然减弱对水汽来源切断的响应时间大约为12 h；对流层中低层水汽辐散区的出现，抑制了低层水汽向高层输送，导致“尤特”突然减弱；在其减弱过程中，贯穿对流层的位涡柱高值区不断向对流层中层收缩并加强，同时与平流层高位涡区迅速分离；在热带气旋“尤特”突然减弱前6 h，环境风垂直切变突然增大，同时在“尤特”不断减弱的过程中，环境风垂直切变呈现总体逐步增大的趋势。

Mechanism on rapid weakening of tropical cyclone "Utor" (2006) over the South China Sea

Based on NCEP/NCAR reanalysis data, the mechanism on rapid weakening of tropical cyclone “Utor” over the South China Sea was analyzed. The results show that the breakdown of water vapor sources is the necessary condition of sudden weakening of tropical cyclone “Utor”, and its response time to the breakdown is about 12 hours. Water vapor divergence region occurs in low and middle layer of troposphere, which restrains the transport of water vapor from the low to the high and makes “Utor” weakened suddenly. The high value region of potential vorticity through troposphere reduces continuously and strengthens to middle layer of troposphere when “Utor” is weakening, and it is separated rapidly from the high value region of potential vorticity at stratosphere. Vertical shear of environmental wind strengthens suddenly before 6 hours of rapid weakening of “Utor”. As a whole, vertical shear of environmental wind strengthens gradually in the course of weakening of “Utor”.