台风“米克拉”(2006)近海急剧加强的成因分析

Analysis on the causes of rapid intensification of typhoon "Mekkhala" (2006) in nearshore waters

应用NCEP GDAS/FNL再分析资料及中央气象台台风路径资料,从环流形势、环境条件与地形作用的角度分析了台风“米克拉”近海急剧加强的成因,并对其加强前后的湿位涡演变特征进行诊断。结果表明:南亚高压与西太平洋副热带高压对台风“米克拉”强度突增具有重要作用。稳定的南亚高压提供良好的高空出流,西伸加强的西太平洋副热带高压引导台风“米克拉”快速北上并在后期向西偏移,有利于增大气压梯度力和维持水汽输送。西南季风和越赤道气流为台风“米克拉”加强提供水汽和能量。台风“米克拉”水汽通道主要位于东侧,强水汽辐合集中于南侧,进入台湾海峡后水汽输送与辐合也随之加强。弱的垂直风切变和较暖的洋面利于台风“米克拉”发展。台湾海峡的狭管效应也具有不可忽视的增幅作用。从湿位涡正压项来看,台风“米克拉”加强前低层以负值区为主,成熟后逐渐被正值区替代,反映了其暖心结构的演变特征。湿位涡斜压项的变化相对复杂,主要趋势是湿斜压性整体加强,梯度变化更加剧烈,且700 hPa上斜压项东正西负的分布演变为北正南负。

Based on the NCEP GDAS/FNL reanalysis data and CMA tropical cyclone track data,this paper analyzes the cause of rapid intensification of typhoon "Mekkhala"(2006) in nearshore waters from the perspective of circulation patterns,environmental conditions and topographic effects,and diagnoses the evolution features of moist potential vorticity(MPV) before and after the intensification.The results show that the South Asia high and West Pacific subtropical high play an important role in the rapid intensification of typhoon "Mekkhala".The stable South Asia high provides a favorable upper-level outflow,and the westward extended and intensified West Pacific subtropical high lead typhoon "Mekkhala" to move northward quickly and to move westward in the later stage,which is favorable for increasing the pressure gradient force and maintaining the water vapor transport.The southwest monsoon and cross-equatorial flow bring abundant vapor and energy to typhoon "Mekkhala".The water vapor channel of typhoon "Mekkhala" is mainly located in the east side,while the strong water vapor convergence is concentrated on the south side.The vapor transport and convergence is strengthened after typhoon "Mekkhala" entering the Taiwan Strait.The weak vertical wind shear and warmer sea surface is favorable for the development of typhoon "Mekkhala",and the narrow pipe effect of the Taiwan Strait is also unneglectable in its enhancement.In terms of the barotropic term of the moist potential vorticity,the lower layer of typhoon "Mekkhala" is dominated by negative areas before strengthening,and is gradually replaced by positive areas after it is mature reflecting the evolution characteristics of its warm core structure.The baroclinic term of the moist potential vorticity varies relatively more complicated with the main trend of overall strengthened baroclinicity and more intensified gradient variation.Moreover,the distribution of the baroclinic term of the moist potential vorticity above 700 hPa changes from positive to the east and negative to the west to positive to the north and negative to the south.