超强台风Saomai(0608)加强成因分析及 海温影响的数值试验研究*

以严重影响我国的2006年8号超强台风Saomai为研究对象,首先从大尺度环流特征和物理量场对其登陆前强度不断加强成因作诊断分析,指出台风加强与副高的加强和南落、低空持续加强的水汽输送、高空流出气流的强辐散、台风移向垂直切变小值区和暖洋面密切相关。然后,利用中尺度数值模式MM5分析了海温高低对台风强度变化的影响,试验结果表明台风强度对海温十分敏感,海温改变可以引起台风强度的迅速变化,海温降低2℃将使台风最终减弱19hPa。边界层通量的分析表明,海温变化对台风强度的影响中潜热通量的作用是主要的,而感热输送的作用较小。就海温变化是否引起诸多台风强度影响因子分析发现,高海温使台风区域低空气旋式环流和高层辐散流出加强,导致低空更多的水汽向该区辐合,暖海面上空潮湿空气的辐合上升释放大量的凝结潜热为台风的发展加强提供了更多的水汽和能量。对比试验还表明,正位涡向下输送预示着台风将快速加强。另外,本次试验中海温变化对台风移动路径影响不明显, 因而对环境风的垂直切变影响较小。

ANALYSIS ON CAUSES OF STRENGTHENING OF SUPER STRONG TYPHOON SAOMAI(0608)AND NUMERICAL EXPERIMENTS OF THE IMPACT OF SST ON ITS INTENSITY

The study is carried out on 0608 super strong typhoon Saomai which affected East China seriously.Based on the characteristics of large-scaled circulation and physical conditions, the causes of the quick strengthening are analyzed.The results show that the quick strengthening is associated with the enhancement and south-ward moving of subtropical high, lower layer moisture transportation, upper level strong divergence, the moving of typhoon where the vertical shear is little, and high sea surface temperature(SST). By using MM5 model, the changes of intensity are studied when SST is reduced.The results demonstrate that the intensity of typhoon is largely and quickly sensitive to the variation of SST.Sensitive experiment shows that if SST is reduced by 2℃, the intensity of Saomai would be weakened by 19hPa compared with the control experiment.Analysis of boundary layer flux reveals that the latent heat flux plays a major role in such a change and the influence of sensitive heat flux is little.The factors concerning the strengthening of typhoon caused by the change of SST are also analyzed.It is found out that warmer SST makes the enhancement of both cyclonic circulation at lower level and divergence at higher level, which lead to more convergence of wet air over sea and release plentiful latent heat which is helpful to Saomais development.Contrast experiments also demonstrate that the downward transmission of oppositive potential vorticity indicates the strengthening of typhoon.It is worth mentioning that in both experiments the track of typhoon is not sensitive to the change of SST, so SST change has little effect on vertical shear of environment wind.