The Long Term Features of Tropical Cyclones AffectingTaiwan

• Main Authors: Yueh-Shyuan Wu, 吳悅瑄
• Other Authors: Cheng-Shang Lee
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/uxqbj9

碩士 === 國立臺灣大學 === 大氣科學研究所 === 106 === The purpose of this study is to analyze the long-term features of TCs affecting Taiwan. The large-scale environments related to these features are discussed to help understand the possible mechanisms. This study analyzes the TCs occurred in the targeted area (118°-125°E, 20°-27°N) during 1970-2013, using the wavelet analysis approach. Results show that there are two significant scales, interannual (3-5 year) and interdecadal (10-13 year) signals about the TC numbers in the area. To address the large scale mechanism, an empirical orthogonal function (EOF) analysis is applied on the 3-5 year and the 10-13 year filtered 500 hPa wind fields and geopotential heights. Results show that the interannual signal is dominated by the 500 hPa U- and V-wind fields, suggesting that the TC track patterns are affected mainly by the mid-level flow. On the other hand, the interdecadal signal is dominated by the 500 hPa U-wind field and geopotential anomalies, indicating that the main cause of the difference in TC number near Taiwan is the location of TC formation. In addition, to discuss the relationship between the large scale flow patterns analyzed by EOF and the synoptic environmental circulations, a non-hierarchical cluster analysis is applied on 850 hPa wind field associated with TCs which have potential to affect Taiwan. For both interannual and interdecadal scales, the low-level synoptic-scale steering flows dominate the TC track patterns that lead TCs to affect Taiwan. Moreover, the locations of TC formations are also changed in interdecadal scale and influence the pattern of TC track affecting Taiwan. The features of wind field, geopotential height, and TC formation location obtained by EOF analysis are similar to those obtained based on the cluster analysis, indicating that the number of TCs affecting Taiwan does have interannual and interdecadal variabilities and is affected by the changes in the synoptic environment.