环境因子对南海土台风“蝴蝶”与“银河”强度的影响*

选取了两例迅速增强的南海土台风“蝴蝶”(1321)与“银河”(1603), 分析了其增强时南海及周边海域的高低空环流形势、垂直风切变情况和海洋热状况, 并利用WRF (Weather Research and Forecasting Model, WRF)模式探究两者强度不同的环境原因。“银河”虽具有较有利的海洋下垫面条件, 但并未发展为台风, 是因为不利的高低空环流形势和垂直风切变条件。“蝴蝶”迅速增强为强台风是因为其发生时北方冷空气南下, 西南暖湿气流爆发等有利条件。WRF模式对海表面温度(SST)影响土台风强度的敏感性实验表明, 土台风强度对于SST的响应表现为非线性正相关, SST升高, 土台风增强的速率将减缓。7—9月的南海SST均高于28℃, 已满足土台风增强条件。因此, 在对于土台风的预报中, 需特别注意SST以外的其他环境因子。

Effect of environmental factors on the intensity of Typhoons Wutip and Mirinae in the South China Sea

We selected two rapidly intensifying, locally-originated typhoons Wutip (1321) and Mirinae (1603), and analyzed upper- and low-level circulations, vertical wind shear, and ocean heat content in and around the South China Sea during typhoons’ passages over the sea. We also used WRF (Weather Research and Forecasting Model) model to discuss the environmental factors for their different intensities. Although the underlying conditions were more favorable for Mirinae, it did not develop into a strong typhoon due to weak upper- and low-level circulations and strong vertical wind shear. On the contrary, Wutip developed into a super typhoon rapidly due to the cold southward airflow and the outburst of warm humid air from the southwest. The results from WRF model’s sensitivity experiments about the effect of sea surface temperature (SST) on the intensity of locally-originated typhoon indicated that locally-originated typhoon intensity and SST have nonlinear positive correlation. However, as SST increases, the intensification trend of locally-originated typhoon slows down. From July to September, the SST in the South China Sea is higher than 28℃, meeting the condition for typhoon intensification. Therefore, attention should be paid to different environmental factors other than SST in locally-originated typhoons’ forecast in the South China Sea.