臺灣博碩士論文加值系統

2003年6月7日伴隨梅雨鋒面的移動在台灣南部海域引發顯著的中尺度降水現象。根據當日的雨量觀測，屏東縣瑪家降下379.5 mm的雨量達到超大豪雨的標準。自0000 UTC開始，墾丁雷達首先觀測到數個零星的對流胞發展且逐漸形成線狀系統。在線狀系統形成後，回波逐漸呈現彎曲的型態。隨著時間的發展，該回波更進一步形成波型線狀回波(Line Echo Wave Pattern, LEWP)。在整個降水過程中，共觀測到三個波型回波。整個降水系統持續超過六小時以上且生命期波型回波最長的達四小時。
WRF (Weather Research and Forecasting) 模式的模擬結果顯示出下列特徵：(1)可模擬出三個波型回波的型態，但位置偏南。(2)扣除系統移速後，於2 km定高面上波型回波的北側有逆時針渦旋出現，但南側卻無順時針渦旋。(3)在這些波型回波的垂直結構上，系統後方高空有出現相對較乾冷的空氣。該氣流從3-5 km高度向系統前方移動並通過降水區下沈接近地面。然而，卻沒有出現由前往後的氣流(Front to Rear Flow)。(4)波型回波北側之渦旋強度大約為10-3 s-1，較中緯度地區伴隨弓狀回波的渦度小。(5)0-4 km之水平風速差平均為11 ms-1，也較中緯度伴隨弓狀回波之上下層風速差小。(6)由9公里水平網格的模擬結果顯示波型回波的北側渦旋是梅雨鋒面上的中尺度渦旋。渦旋西北側有乾冷的西北風，東南側有暖濕的偏南風。因此，伴隨中尺度渦旋的水平風切是造成波型回波的動力因素。整體而言，個案模擬的特徵與中緯度地區典型的弓狀回波或颮線結構不同。
在不同的雲微物理靈敏度測試中：(1)Kessler法無法有效生成波型回波。Lin et al.法僅在台灣西南側生成一個波型回波。(2)WSM 3-Class法在降水分布上有較合理的表現，但在台灣南部山區的總降雨量偏低。僅有一個波型回波出現且移動方向較偏南、生命期也較長。(3)WSM 5-Class法可模擬出三個與觀測相符的波型回波。此外，總降水量及降水分布亦較其它三者接近實際觀測結果。
在降水蒸發率之熱力靈敏度測試中：(1)當蒸發率低於50%時，對流系統無法有效組織成波型，且移速也減緩。(2)蒸發率的改變，似乎僅對低層大氣（小於1 km）的溫度改變產生影響。(3)當蒸發率為原來80%時，模擬的三個波型回波，其出現的時間及生命期與實際接近，累積降水分布及降水量也與實際相似。(4)在不同蒸發率測試中，回波平均移速與地面冷池移速沒有顯著改變。(5)原則上，在WSM 5-Class的微物理參數法下，減少降水蒸發率對於回波的移速沒有明顯地影響，故對波型回波的產生影響不大。

A mesoscale convective system induces a heavy rainfall event while propagating to southern Taiwan area on 7 June 2003. The precipitation at Ma-chia station accumulates 379.5 mm rainfall per day, which reaches extremely torrential rainfall level defined by Central Weather Bureau. A line echo organized by several convective cells was observed by Ken-ting radar since 0000 UTC. The line system bends and evolves into a line-echo wave pattern (LEWP) gradually. In LEWP, there existed three wave-like echoes during the evolution of the system. The longest lifetime of these wave-like echoes is over 4 hours while whole system sustains over 6 hours.
Some characteristics of WRF model simulation are listed as below:
(1) Three wave-like echoes are located further south comparing to that in the observation.
(2) A cyclonic vortex appears at the northern end of those wave-like echoes from system-relative speed at 2 km level, but it can’t find the anti-cyclonic vortex at the southern.
(3) A rear-inflow in the vertical structure of the wave-like echo, which is colder and dryer, propagates from 3 or 5 km level behind the system, and descends to ground inside the convective zone. However, the front to rear flow is absent.
(4) The vorticity of those cyclonic vortex are over 10-3 s-1 which are weaker than that of midlatitude counterpart.
(5) The average vertical shear between 0 and 4 km in altitude is 2.75×10-3 s-1, which is also weaker than that in midlatitude environment. Consequently, the characteristics of the simulated case study show that the present wave-like echo is different from the bow echo and a squall line existed in midlatitude.
(6) The results analyzed from a simulation of 9 km horizontal grid show that the cyclonic vortex existed at the northern end of wave-like echo is collocated with the mesovortex associated with Mei-Yu front. A dry cold flow exists at the northwest of the vortex, and a moist warm southerly wind exists at the southeast of the vortex. Therefore, the dynamic mechanism of horizontal shear associated with mesovortex triggers the wave-like echo.
A sensitivity test of microphysics illustrates that:
(1) The Kessler scheme can not provide a generation of wave-like echo. The Lin et al. scheme can trigger only one wave-like echo in the southwest Taiwan area.
(2) The WSM 3-Class scheme parameterization is valid for the precipitation distribution, however the total rainfall rate is less than that of observation. And only one wave-like echo shows up propagating toward south with longer life cycle.
(3) The WSM 5-class scheme parameterization is valid for three wave-like echoes which are comparable with real observations. And the precipitation distribution is also better than other schemes.
A sensitivity test for precipitation evaporation shows that:
(1) Below 50% evaporation rate, the wave-like echo can not be triggered.
(2) With the WSM 5-Class scheme, the changes of evaporation rate only affect the temperature field in the lower atmosphere.
(3) With the 80% evaporation rate, those wave-like echoes have the same lifetime and accumulating rainfall rate as the real case.
(4) The averaging moving speed of the wave-like echo B and cold pool have never been affected due to different evaporation rate.
(5) In principle, the decreasing evaporation rate by applying WSM 5-class scheme will not influent moving speed of line echo and formation of wave-like echoes.

誌謝 ii
摘要 iii
ABSTRACT v
目錄 vii
表目錄 ix
圖目錄 x
1. 緒論 1
1.1 前言 1
1.2 研究動機及目的 6
1.3 論文架構 8
2. 個案資料來源及分析 10
2.1 研究資料的來源 10
2.2 個案綜觀氣象環境分析 12
2.2.1 地面與高空天氣圖分析 12
2.2.2 探空圖分析 12
2.2.3 衛星雲圖分析 17
2.3 雷達資料分析 17
2.3.1線狀對流的形成 17
2.3.2 線狀回波的轉變 21
2.3.3 通過台灣南部的波型回波 21
2.3.4 中尺度降水系統之結構分析 21
3. 模式簡介與實驗設計 28
3.1 模式簡介 28
3.2 實驗設計 31
4. 研究結果與討論 34
4.1 模擬結果 34
4.1.1 綜觀天氣結果 34
4.1.2 波型回波的類型 38
4.2雲微物理參數靈敏度測試 50
4.2.1 Kessler Scheme模擬結果 50
4.2.2 Lin et al. Scheme模擬結果 50
4.2.3 WSM 3-Class模擬結果 51
4.3 雨水蒸發測試及結果分析 55
4.4.1 兩倍雨水蒸發率的結果 55
4.4.2 40%及50%雨水蒸發率的結果 56
4.4.3 60%雨水蒸發率的結果 56
4.4.4 80%雨水蒸發率的結果 56
4.4.5雨水蒸發率結果分析 57
4.4 綜合討論分析 67
5. 結論及未來展望 71
參考文獻 73
自傳.…………………...…………………………………………………………....78

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