多时间尺度环流对台风“天鹅”(1515)突变路径的影响

利用NCL滤波方法将NCEP提供的FNL风场资料分离出天气尺度,准双周振荡(QBWO,Quasi-Biweekly Oscillation)和热带季节内振荡(MJO,Madden-Julian Oscillation)环流场,研究不同时间尺度环流对台风"天鹅"(1515)突变路径的影响。台风路径的特征能够分3个阶段,其中第二阶段台风发生突然转折。第一阶段,天气尺度上台风东侧的反气旋和QBWO环流场中的波列共同引导台风向西偏北方向运动,而MJO环流场中的引导气流作用较小;第二阶段,天气尺度上台风东侧的反气旋和低频环流场中台风附近的气旋共同促进了"天鹅"近90°的突然转向,其中,高、低频分量分别促使台风突然向北、向东转向;第三阶段,天气尺度上的气旋与反气旋、QBWO环流场中的反气旋以及MJO环流场中的脊共同引导"天鹅"向东北方向运动,其中MJO环流场中气旋附近的偏东风促使"天鹅"向西运动,但由于它被天气尺度上强烈的偏西风所抵消,故"天鹅"仍向东运动。

Effects of multi-time scale circulation on the sudden track of Typhoon Goni(1515)

The influence of different time-scale circulations on the sudden track of the Typhoon Goni (1515) was analyzed by filtering the synoptic-scale, QBWO (Quasi-Biweekly Oscillation), and MJO (Madden-Julian Oscillation) circulation fields from FNL wind field data. The moving path of Goni can be divided into three stages, and the sudden track appeared in the second stage. In the first stage, the anti-cyclone east to Goni in synoptic-scale circulation and the wave train in QBWO circulation field lead the cyclone to move towards northwest. The effect of the steering flow in MJO circulation is weak. In the second stage, the anti-cyclone east to Goni in synoptic-scale circulation and the cyclone in low-frequency circulation field promote a sudden transition with a right angle of the cyclone. The synoptic-scale propagation leads Goni to transfer northward, and the low-frequency propagation leads Goni to transfer eastward. In the third stage, the anti-cyclone and the cyclone in synoptic-scale circulation field, the anti-cyclone in QBWO circulation field and the ridge in MJO circulation field lead the cyclone to move northeast. The easterly wind from the cyclone in MJO circulation field lead Goni to move westward, but Goni still moves eastward because the easterly wind is negated by strong westerly wind in synoptic-scale circulation field.