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標題: | 西北太平洋熱帶雲簇之形成與發展 Formation and Development of Tropical Cloud Cluster in the Western North Pacific |
作者: | Hsu-Feng Teng 鄧旭峰 |
指導教授: | 李清勝(Cheng-Shang Lee) |
共同指導教授: | 許晃雄(Huang-Hsiung Hsu) |
關鍵字: | 熱帶雲簇,熱帶氣旋形成,熱帶雲簇發展過程,群落分析,年際變化, tropical cloud cluster,tropical cyclone formation,development of tropical cloud cluster,cluster analysis,interannual variation, |
出版年 : | 2016 |
學位: | 博士 |
摘要: | 熱帶雲簇為熱帶氣旋的前身,為完整了解西北太平洋熱帶氣旋形成之長期統計特徵,本研究建立一組長時間之熱帶雲簇資料,分析熱帶雲簇之形成與發展成熱帶氣旋的過程,並探討其年際變化。本研究利用客觀方法追蹤西北太平洋於1981‒2009年7‒10月間形成之2248個熱帶雲簇;分析結果顯示,相較於熱帶氣旋,熱帶雲簇之形成過程對環境條件的變化更為敏感,且其數量在西北太平洋次區域(以140°E為界)內有顯著之年際變化。然而,雖然次區域內的熱帶雲簇與熱帶氣旋形成數量皆與聖嬰現象有顯著相關,但熱帶氣旋與熱帶雲簇數量的比例(熱帶氣旋形成率)並不隨聖嬰事件而有顯著改變;即次區域內熱帶氣旋形成數量隨聖嬰事件的變化,主要是因熱帶雲簇數量改變所致。透過偏相關分析與蒙地卡羅模擬,亦驗證聖嬰現象顯著影響西北太平洋環境參數之變化,進而導致熱帶雲簇數量之改變。
另一方面,為了解不同環境類型下形成之熱帶雲簇的特徵,本研究透過非層析群落分析法,針對熱帶雲簇與熱帶氣旋形成時所伴隨之850hPa環流進行分類。結果顯示,熱帶雲簇形成之環境可合理分為8類、熱帶氣旋形成之環境則可分為5類;於不同環境類型下形成之熱帶雲簇數量、位置、對流結構及發展成熱帶氣旋的比率皆有顯著差異,其受聖嬰事件的影響情況亦不同。此外,分析不同環境類型下熱帶雲簇發展成熱帶氣旋之過程顯示,在季風(東風)環境類型中,熱帶雲簇平均形成環境條件較佳(差),但會持續發展成熱帶氣旋之雲簇與不會持續發展成熱帶氣旋之雲簇間,有利其發展之環境條件無(有)顯著差異,且熱帶雲簇發展至熱帶氣旋所需之時間較長(短)。為了解造成不同環境類型下熱帶雲簇發展時間差異之原因,本研究分析熱帶雲簇內中尺度對流之特徵與角動量通量之變化。結果顯示,在東風環境類型雲簇發展過程中,中尺度對流數量少但分布位置靠近雲簇中心,使對流加熱較集中,且具較佳的天氣尺度中層動力條件;而在季風環境類型雲簇發展過程中,雖然初始環境條件較佳且中尺度對流數量多,但中尺度對流分布位置分散,使對流加熱較不集中,且顯著之天氣尺度角動量內傳是由低層向中高層發展。這些特徵差異,即造成東風與季風環境類型之熱帶雲簇發展成熱帶氣旋所需時間不同。 Tropical cloud clusters (TCCs) are precursors to tropical cyclones (TCs). To fully understand the long-term statistical features of TC formation, this study establishes climatological TCC data for the western North Pacific (WNP) and analyzes the formation, development, and interannual variation of TCCs. During July–October 1981–2009, a total of 2248 TCCs were objectively identified using infrared satellite images. Results showed that in comparison to the formation of TCs, the formation of TCCs is more sensitive to the environmental conditions and more significantly correlated with El Niño–Southern Oscillation (ENSO) signal in the sub-region of WNP (separated by 140°E). While more (less) TCCs and TCs form in the eastern (western) part of the WNP during El Niño years than during normal years, the converse is true during La Niña years. The ratio of TC numbers to TCC numbers (TC genesis productivity) does not correlate with the Oceanic Niño Index even in the sub-regions of the WNP. The influence of ENSO on the TC numbers in each sub-region of the WNP is mainly due to the changes in TCC numbers, and not the changes in TC genesis productivity. To further understand the importance of the ENSO signal on the TCC activity, partial correlations and Monte Carlo simulations were used to reflect the influence of ENSO on TCC activity through the environmental parameters in each sub-region. Further, to understand the environmental circulation patterns associated with TCC and TC formation, a non-hierarchical cluster analysis was applied using 850hPa wind field based on the locations of TCC and TC formation. As a result, eight types of TCCs and five types of TCs were efficiently analyzed in the classification procedure. The numbers, locations, convective structures, and developing ratios were found to be quite different for each type of TCC. In addition, the influence of ENSO on different types of TCCs was also different. Contrastingly, the development of different types of TCs from different types of TCCs was also analyzed. For the easterly-type TCC development, the developing cases were found to have more favorable initial conditions than the non-developing cases, and the TCCs were found to develop into TCs in shorter time periods. However, for the monsoon-type TCC development, no significant difference was found in the initial conditions between the developing and non-developing cases, and the TCCs needed more time to develop into TCs. To understand the reason underlying the significant differences in the development time of different TCC developments, the features of mesoscale convective system (MCS) and angular momentum flux were analyzed. Results showed that for easterly-type TCC development, while the number of MCS is less, the distribution of MCS is more concentrated, and better weather-scale dynamic conditions exist at mid-level. For monsoon-type TCC development, although the initial conditions are more favorable and the number of MCS is more, the distribution of MCS is not concentrated, and the significant weather-scale inward angular momentum develops from low-level to mid- and high-level. These different features thus result in different development times of TCCs into TCs in the easterly-type and the monsoon-type TCC development. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/49953 |
DOI: | 10.6342/NTU201602202 |
全文授權: | 有償授權 |
顯示於系所單位: | 大氣科學系 |
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