环境场对西北太平洋热带气旋快速增强过程的影响

利用美国联合台风预警中心整编的西北太平洋1970—2012年热带气旋(TC)最佳路径数据集及ERA-Interim再分析资料,利用极端天气法确定TC快速增强(RI)的阈值为30 kn,分析了快速增强(RI)TC的时空分布特征;从RI的样本中选取9个个例,采用动态合成分析法,对TCRI过程的环境场进行比分析。研究表明:(1)菲律宾群岛以东(10~15°N,130°E)海域为RI发生频数最多的区域,南海地区发生RI的情况明显偏少。(2)RI在1972年发生的概率最大,而在2005年发生的概率最小,1997年后,RI发生的概率波动性较大。(3)西风与西南风水汽输送结合150h Pa附近的反气旋强辐散作用,有利于TCRI过程的进行。(4)RI发生前24 h至RI发生后的6 h,TC中心附近区域平均东风切变较快增大,其值由0.5 m·s~(-1)增加到2.5 m·s~(-1)左右,之后保持在2.0~3.0 m·s~(-1),使TC处于一个有利于其RI过程的纬向风切变环境。

Effect of environment field on rapid intensification process of tropical cyclones over the western North Pacific

Based on the best track data of Tropical Cyclone (TC) in the western North Pacific during 1970-2012 from the Joint Typhoon Warning Center (JTWC) and the ERA-Interim reanalysis data, the extreme weather method was used to determine 30 kt as the threshold of Rapid Intensification (RI), moreover, the temporal and spatial distribution features in RITCs were analyzed. In addition, nine cases from RI samples were selected to conduct comparative analysis on the environmental field of TCRI process by using dynamic composite analysis technique. Results show that (1) RI occurs most frequently in the ocean about 5° east of the Philippine Islands (130°E, 10-15°N), while rarely happens in the South China Sea. (2) RI occurred most possibly in 1972, while least in 2005, and the possibility fluctuation was larger after 1997. (3) The transportation of westerly and southwesterly water vapor associated with the divergence of anticyclone at 150 hPa promotes TCRI activity because of suction effect. (4) During the 24 h before RI and 6 h after RI, the vertical zonal wind shear of the easterly strengthens gradually near the central region of TC, whose value increases from 0.5 m·s^-1 to 2.5 m·s^-1, then varies between 2.0-3.0 m·s^-1, which provides a moderate vertical zonal wind shear near the center of TC to make TCRI conduct.