异常北折台风“洛坦”与异常西折台风“奥玛”路径的对比及预报

Comparison and prediction of unusual-turning tracks of typhoons Nock-ten and Orma

选取在台湾岛附近发生异常北折的台风“洛坦”和异常西折的台风“奥玛”,对其环流形势进行对比分析,之后将全风场分解为气候场和瞬时扰动风场,应用扩展的β-平流模型对“洛坦”和“奥玛”的异常偏折路径进行预报尝试。结果表明:1)两个台风的500hPa全风场分析表明,副高及槽前西南气流为“奥玛”异常北折的主要影响系统;而“洛坦”北侧的大陆高压与副高合并加强有利于其西折。2)扰动风场的分布表明,北折“洛坦”南侧的西南风逐渐增大,东侧的东南风逐渐转变为南风,在异常偏折时刻形成一条向北的“输送带”利于其北折;西折“奥玛”在其异常偏折过程中其北侧一直维持着一个反气旋性环流,向西输送分量逐渐增加,利于其西折。3)利用扩展的β-平流模型对两个台风路径进行预报,发现在综合考虑气候态和扰动场时,“洛坦”的路径预报效果最好,而考虑瞬时扰动场时“奥玛”的西折预报效果最好。

In this paper,the circulations of Typhoon Nock-ten with abnormal northward turning and of Typhoon Omar with abnormal westward turning near Taiwan Island are analyzed and compared.The total flow is decomposed into climatic and anomalous flows,and the abnormal turning paths of Nock-ten and Omar are forecasted by using the beta-advection model.The results are as follows.1)Analyses of total flow at 500 hPa reveal that the main influencing environmental systems include the western North Pacific subtropical high and the west trough during the period of unusual north-turning;the western North Pacific subtropical high and the Continental high merged and consolidated at the north and one typhoon in the southeast,which favored Orma’s unusual western turning.2)Anomalous flows manifested that southwesterly wind gradually aggrandized on the south side of Nock-ten,the southeasterly wind gradually changed into southerly wind on the east side,forming a northwardly"belt"at the unusual north-turning time;there maintained an anticyclone during the unusual west-turning time on the north side of Orma.3)The generalized beta-advection model is applied to identify the tracks of Nock-ten and Omar.Results show that the north-turning Nock-ten track is forecasted well by considering the climatic and anomalous flows,whereas the west-turning Orma is forecasted well with the consideration of anomalous flow.