Vertical wind shear and tropical cyclogenesis in the South China Sea
首发时间:2015-09-29
Abstract:Tropical cyclones occur frequently in the South China Sea (SCS) and could cause serious disasters. The effects of vertical wind shear (VWS) on tropical cyclogenesis in the SCS were examined by using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data during the period of 1997-2006. A relationship between the distribution of ten-year mean VWS and the genesis locations of TCs in the SCS was revealed. The results show the effects of the background mean VWS on TC formation in the SCS. TCs were formed in the northern SCS during the summer monsoon and in the southern SCS during the winter monsoon, with mean VWS below 20 m/s. No TCs formed in the southern part of the SCS during the summer monsoon nor in the northern part during the winter monsoon, both of which coincided with strong mean VWS above 20 m/s. The mean VWS in three days prior to TC formation in regions within 300 km around the TC genesis locations was calculated for 36 tropical cyclogenesis events in the SCS during the period from 1999 to 2006. The value of this mean VWS in the SCS was 9.69 m/s, which was slightly less than the ten-year monthly mean VWS (10.22 m/s). The results suggest that there were no significant changes in the VWS before tropical cyclogenesis within 300 km around the TC genesis locations in the SCS. By comparing the mean VWS in three days prior to TC formation and the ten-year monthly mean VWS for these 36 cyclogenesis events, a high VWS changing center with a VWS increment exceeding 8 m/s in three days prior to TC formation was found to occur to either the north or the south of the TC genesis location in 28 of these 36 events. The results give us helpful information when doing forecast for TC genesis in the SCS.
keywords: tropical cyclone South China Sea cyclone genesis vertical wind shear
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南海海域垂直风切变与热带气旋生成
摘要:热带气旋在南海海域生成活动活跃,可以造成严重的自然灾害。利用NCEP/NCAR再分析资料分析了南海海域垂直风切变对南海热带气旋生成的影响。结果显示南海热带气旋的生成位置与垂直风切变的空间分布存在关系,表明垂直风切变对南海热带气旋生成可以产生影响。热带气旋在夏季生成于南海北部而在冬季生成于南海南部,生成区域的垂直风切变大小均小于20m/s。没有热带气旋在夏季生成于南海南部和冬季生成于南海北部,这些区域对应的垂直风切变均大于20m/s。计算了在1999至2006年期间南海海域生成的36个热带气旋在生成前3天对应的垂直风切变,得到的平均值为9.69m/s,略小于气候态月平均的垂直风切变(10.22m/s)。结果表明南海热带气旋生成前在生成位置附近垂直风切变没有发生显著的变化。通过对比热带气旋生成前和气候态平均的垂直风切变的空间分布,发现28个气旋生成个例中在热带气旋生成位置的南部或者北部出现超过8m/s的垂直风切变的增加。这些结果有助于我们对南海热带气旋的生成进行早期的预警。
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No.4655549957347144****
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