A study of Typhoon Size in the Western North Pacific

• Main Authors: Wei-Ting Fang, 方偉庭
• Other Authors: Cheng-Shang Lee
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/54704116445173703691

碩士 === 國立臺灣大學 === 大氣科學研究所 === 96 === This study uses QuikSCAT satellite to estimate the radial extents of 15 m s-1 wind (R15) of the tropical cyclones (TCs) occurring over the western North Pacific from 2000 to 2005 (145 TCs). The results of analyzing of the development during the R15 changing from tropical storm (TS) to typhoon (TY) show that if the R15 of a TC is relatively large (> 1.8°) (, or small (< 1.1°)) when it develops to TS, there is a 70% (67%) of possibility for it to remain as a large TC (> 2.6°) (, or small (< 1.8°)) when it intensified to TY. In other words, a TC tends to retain its size during the development of the intensity from TS to TY. The composite analyses show that there are strong southwesterly and easterly (> 10 m s-1) at 850 hPa to both the north and the south of the large cases within 72 h before their intensity to 34 kt, and especially the southwesterly increase about 5 m s-1 during the period. However, the synoptic flows of small cases are relatively weak, and remain almost the same during the whole process. Furthermore, when large cases move from the south to the west of subtropical high (STR), the small cases move with STR by lingering around its southern edge. Aere (2004) and Roke (2005) are selected cases respectively represent large and small cases considering their associated synoptic flows are similar to composite wind field. The 10 m radius section shows that the wind speed of Aere increases not only at the inner but also the outer core, and the area of wind speed above 10 m s-1 extends to 8° radius; nevertheless, the 10 m wind speed of Roke increases at inner core only. The angular momentum flux analysis also shows the angular momentum flux of Aere extends over 10°, which is much larger than that of Roke. Therefore, if there is a southwesterly surge located to south of a large TC during the formation stage, the TC tends to be with large size.