3月份在南海生成的1201号强热带风暴“帕卡”的移动特征及成因分析

Analysis of the causes and moving characteristics of 1201 strong tropical storm Pakhar generated in the South China Sea in March

1949～2011年中国气象局台风年鉴资料统计结果表明,在南海生成的热带气旋,1、2月份仅在1965年出现1次,而3月份没有热带风暴强度级别以上的热带气旋生成,1201号强热带风暴"帕卡"是首个3月份在南海生成的强热带风暴,本文指出"帕卡"具有生成时间偏早、移动速度慢等显著特征,其平均移动速度仅为1.6 m/s.利用Nino 3.4区3月表层水温滑动平均资料、分辨率为2.5°×2.5°的NCEP/NCAR再分析资料、分辨率为1°×1°的NOAA OI表层水温资料,分析了"帕卡"生成原因,结果表明2011年秋冬季拉尼娜事件引起次年3月赤道西北太平洋及南海表层水温较多年平均偏高,其中南海中部表层水温较多年平均偏高0.5℃以上;3月份副高脊线偏北,弱冷空气南下产生的冷涌作为CISK的启动源;南海中南部上空对流活跃,跨赤道气流强劲;低层垂直风切小于5 m/s等有利因素促进了"帕卡"生成.分析结果为春季热带气旋的预报提供有意义的参考.

China meteorological administration typhoon yearbook data （1949 -2011 ） shows that tropical cyclones generated only once in January and February（ 1965 ） in the South China Sea, and no tropical cyclones above tropi- cal storm level were generated in March. 1201 strong tropical storm（STS） Pakhar is the first STS generated in the South China Sea in March. This paper pointed out that Pakhar was a STS of earlier generation time and of slow moving characteristic, with an average moving speed of only 1.6 m/s. The Nino 3.4 SST sliding average data, the 2.5°×2.5° NECP/NCAR reanalysis data, and the 1°×1° NOAA OI SST data were used to analysis the causes of Pakhar formation： the La Nina events in 2011 autumn and winter caused a higher SST in Northwest Pacific and the South China Sea （0.5℃ higher than the many years average） in March, the features of subtropical high in March, the creation of a cold surge as the initiation source of CISK by the southward movement of weak cold air, active convection over the southern South China Sea and a low-level vertical wind shear less than 5m/s, all these factors favored the formation of Pakhar. The results provide meaningful reference for the spring typhoon forecast.