CHARACTERISTICS AND INFLUENCE FACTORS OF RAPID INTENSIFICATION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC
摘要: 选取西北太平洋上热带气旋(TC)24小时风速变化累积频率达95%所对应的15.4 m/s作为迅速增强(RI)的标准,研究了RI个例的基本特征以及TC自身特征因子与环境因子对RI的作用。结果表明,TC迅速增强过程的持续时间平均为33小时,最长可达78小时,并且TC经过迅速增强过程几乎都达到了台风级别以上,其中,一半以上达到了强台风级别以上。对比迅速增强(RI)和非迅速增强(non-RI)个例得到,RI个例相对于non-RI个例发生区域偏南偏东,两者的移动速度没有明显差异,但RI个例有较大向西移动分量并且前12小时增强较大;相对于non-RI个例,RI个例离最大潜在强度较远并且发生在较暖水区和55%～75%的低层相对湿度的条件下;RI个例发生在较小的垂直风切变和较弱的对流层上层东风气流情况下,由上层槽或冷低压引起的强迫弱于平均状况时RI较易发生。TC前12小时强度变化(DVMX)、海表面温度(SST)和垂直风切变(SHR)是影响迅速增强的主要因子,当DVMX≥6.3 m/s时RI发生的可能性最大,达到17.2%。当有若干个影响因子共同起作用时发生RI可能性显著增加,其中以较大的前12小时强度变化(DVMX≥6.3 m/s)、较高的海表面温度(SST≥29.4 ℃)、较弱的垂直风切变(SHR≤5.9 m/s)、较小的相对涡旋角动量通量辐合(REFC≤-1.6 m/(s·d))、偏东经度(LON≥138.2 °E)和低纬度(LAT≤16.7 °N)共同作用时,RI发生的可能性达到最大,可达66.7%。Abstract: In this study, rapid intensification (RI) of tropical cyclone (TC) was defined as a maximum sustained surface wind speed increase of 15.4 m/s over a 24 h period, which was approximately the 95th percentile of 24 h intensity changes of TCs. By using the TC best-track data in the western North Pacific from the Joint Typhoon Warning Center, the basic characteristics of RI samples were studied, the effects of large-scale environmental factors on RI were discussed, and the RI probability was estimated. The results were as followings.
The average duration of RI over the western North Pacific was thirty-three hours, and the longest duration was seventy-two hours. Almost all tropical cyclones that underwent RI reached typhoon intensity, and more than half of them became intense typhoons. Comparing to non-RI cases, the RI cases preferred forming in farther east and south regions with warmer water. No significant differences were found between the translational speeds of the RI and non-RI cases, but the RI cases had a more westerly component of motion and much larger intensification during the previous 12 h than the non-RI cases. In addition, the RI cases were farther from their maximum potential intensity, and under the condition that the lower-level relative humidity was between 55% and 75% comparing to the non-RI cases. Also, the RI cases were more likely to occur in regions with lower vertical shear, more easterly upper flow, and lower relative eddy flux convergence than the non-RI cases.
The intensification during the previous 12 h (DVMX), sea surface temperature (SST) and vertical shear (SHR) were dominant factors that influenced RI. When DVMX was greater than or equal to 6.3 m/s, the probability of RI was 17.2%, the highest probability for a single factor. The probability of RI can be increased significantly by combining several influence factors together. Among these, the highest probability of RI is 66.7% when great previous 12 h intensity change (DVMX greater than or equal to 6.3 m/s), high sea surface temperature (SST greater than or equal to 29.4 ℃), low vertical shear (SHR less than or equal to 5.9 m/s), low relative eddy flux convergence (REFC less than or equal to -1.6 m/(s·d)), high longitude (LON greater than or equal to 138.2 °) and low latitude (LAT less than or equal to 16.7 °N) worked together.
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