近50年影响中国南海的热带气旋气候变化趋势及成因

Climate change trend and causes of tropical cyclones affecting the South China Sea during the past 50 years

本文主要利用1965–2017年的热带气旋资料,对影响我国南海的热带气旋的频数,路径活动以及影响指数等方面气候变化特征及可能原因进行分析。结果表明:1965–2017年间共有535个热带气旋影响我国南海,主要分布在每年6–11月,年平均频数呈现出显著下降趋势。同时路径活动频数在南海大部分地区同样呈现出明显减少的特征,但在北部湾和台湾海峡海域增多。南海北部海域出现的大尺度环境气流偏西风异常和中低层湿度减弱可能是导致频数下降和路径活动减弱的主要原因。此外,利用气旋活动指数进行分析后,进一步发现我国华南和西南地区受上述热带气旋的影响日趋减弱,同时影响南海热带气旋在南海海域的活动影响呈现出逐年下降的趋势。

Tropical cyclones(TCs)in the South China Sea(SCS)cause serious disasters and loss every year to the coastal and inland areas of southern China.The types of TCs are usually difficult to forecast,and studies on the understanding of the TCs affecting the SCS are lacking.In this study,the authors use the TC data during 1965–2017 from two best-track datasets to analyse the climatic characteristics in terms of the frequency,the track activity,and the influencing indexes of the TCs affecting the SCS and investigate the possible causes.The results show that,during 1965–2017,there were 535 TCs affecting the SCS,mainly occurring from June to November of each year,with the annual average frequency exhibiting a significant downward trend.Meanwhile,the frequency of the track activity in most areas of the SCS also demonstrate a remarkable decreasing trend but an increase in the Gulf of Tonkin and the Taiwan Strait.The large-scale environmental anomalous westerlies and the decrease of humidity in the mid-and low-level over the northern part of the SCS are likely the main causes for the decrease in frequency and the track activity.In addition,the analysis using the cyclone activity index shows that the influence of the before mentioned TCs in southern China gradually decreases,while the influence of TCs in the SCS show a decreasing trend during past decades.