Recently, when we investigated the big recurvature of super typhoon Megi (2010), we noticed that there was a cold air intrusion (CAI) from the northwest to the southeast of China before the sharp turn of Megi, accompanied by a northeast-southwest-oriented cold front located on the eastern coast of China ( Fig.
Although high-quality initial conditions by data assimilation 20 or by the improved initialization technique 21, 22 are beneficial to improve the forecasting accuracy of recurving TC tracks, there is not yet a reliable method to predict a TC recurving track in operational practice. However, because state-of-the-art numerical models generally fall short in capturing the intricacies of the underlying mechanisms of TC recurvature, large errors still exist in the prediction of recurving TC tracks 3, 4, 8, 13. Several studies on modeling TC recurvature have also been carried out for both idealized conditions and real cases 3, 5, 19, 20. In particular, it is found that recurving tracks are closely associated with retreat of a subtropical ridge and approach of a midlatitude westerly trough 3, 5, 7, 8, 9, 13, 14. Previous studies have shown that the recurvature of a TC could be caused or influenced by a number of factors, including the steering flows 6, subtropical high 3, 7, 8, 9, monsoon system 7, 10, 11, 12, midlatitude westerly trough 3, 5, 8, 9, 13, 14, zonal winds in the middle and upper troposphere 15, 16, vorticity advection 17, momentum exchange 3, 8, and beta effect together with the basic current asymmetries 18.
In particular, the prediction of the recurving track of a tropical cyclone is extremely difficult and remains a big challenge to forecasters 3, 4, 5, because a recurving track of a TC involves more complex processes than an un-recurving one 4. Because of a number of diverse and complex factors that influence the movement of a tropical cyclone, considerable uncertainties still exist in track prediction using state-of-the-art numerical models or empirical methods. Due to the disastrous effect of tropical cyclones, an accurate prediction of their tracks is very important to protecting human lives and property 1, 2.
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