海气相互作用对“格美”台风发展的影响研究

Effect of Air-Sea Interaction on Typhoon Kaemi

西北太平洋是全球唯一一年四季都有热带气旋生成的海域,同时,我国沿海紧临该海域,是受热带气旋影响最为严重的国家之一。本文通过建立海气耦合模式,以西北太平洋西边界流系源区为研究区域,通过对"格美"台风的数值模拟结果分析,研究海气相互作用对热带气旋发展的影响,对提高台风的数值模拟及预报水平有重要意义。研究表明:耦合作用引起的海表面温度(SST)降低减弱了台风强度,在模拟前期与实况台风强度更为吻合,在后期弱于实况,而台风移动路径受耦合作用的影响不大。台风移动速度及强度决定了SST降温幅度,降低幅度最大可达4℃以上,但SST对大气的响应具有一定的滞后性,SST下降区在台风移动方向上落后于高风速区。台风中心附近大风的抽吸及挟卷作用引起深层低温海水上涌使得SST降低,该冷尾过程至少持续54小时以上。SST的改变决定了热通量的输送,在SST不变的情况下,近地面层风速影响了热通量的分布。垂直上升对流的加强、减弱与台风强度息息相关,42小时之前不断加强的上升对流运动是台风达到最强的原因,此后下沉运动不断加强,导致台风强度减弱。耦合作用增加台风内部涡度的非对称性,但减弱了中心涡度向高层扩展趋势,这可能是耦合作用通过热力因子间接影响动力结构的途径。

The northwestern Pacific is the only region where tropical cyclones（TCs） are generated all year round.China is one of the countries which are badly affected by TCs.A air-sea coupled model has been developed,focusing on the source region of the northwestern Pacific western boundary current system.Here,typhoon Kaemi is taken as an example to study air-sea interaction.The results show that：The SST cooling induced by the air-sea interaction weakens the typhoon,and the model results are consistent with observation during early simulation.However,42 h later,the simulated typhoon is weaker than the observation.The typhoon track is scarcely influenced by the air-sea interaction.The SST cooling extent is determined by the relationship between typhoon moving speed and intensity and the maximum cooling is more than 4℃.The SST cooling zone drops behind the region of maximum wind speed along the typhoon track.The pumping and mixing induced by winds around the typhoon center bring cold water up and get the SST cooling.Such cold wakes last more than 54 hours.The changing of SST determines heat fluxes transport.Once the SST is constant,the heat fluxes are determined by the low-lying wind.Vertical convection is closely related to the typhoon intensity.Before 42 h,the ascending convection is the reason of typhoon intensification.Hereafter,the downdraft results in typhoon weakening.The coupling adds asymmetry of typhoon vorticity,and prevents its trend of ascending much higher.Maybe this is the mechanism of thermal factor affecting the dynamical structure.