氣膠衝擊颱風之模擬 ─ 納莉颱風(2001)

Simulation of Aerosol Impact on Typhoon Nari (2001)

黃竹君(Chu-Chun Huang)

指導教授 ： 李清勝

共同指導教授 ： 陳正平(Jen-Ping Chen)

國立臺灣大學/理學院/大氣科學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01661

摘要

過去研究顯示，雲微物理過程對颱風路徑、結構及降水有顯著影響；然而針對雲凝結核(CCN)濃度影響颱風結構變化則相對較少。由於氣膠濃度變化能有效改變雲微物理過程，進而可能反饋影響颱風中對流之發展，因此了解氣膠於颱風發展階段的角色有一定程度的重要性。本研究針對2001年納莉颱風，探討不同氣膠濃度對颱風模擬之影響。為適切模擬雲與氣膠在混態雲內之交互作用，因此選用能夠妥善處理雲滴活化過程與冷暖雲機制的CLR雲微物理參數法，將其植入WRF中以模擬納莉颱風。
模擬結果顯示氣膠初始設定與雲微物理法的差異皆會影響納莉颱風路徑、強度、對流及微物理結構。當氣膠濃度較高時，颱風外圍雨帶會有近似較成熟颮線的結構，由於小冰晶的成長較緩，故有較多冰晶存在於高層外流區，使層狀區域水平延伸較廣。層狀雲區亮帶之上的冰晶成長釋放潛熱，其下的蒸發融化作用導致的冷卻，將能加強近地面的冷池及尾端入流，有利對流雲系持續發展。配合環境場的分析顯示，氣膠數量較多時，層狀區域較廣，更有利於上述機制的作用。另一方面，層狀雲區高層因冰相過程的加熱、中低層因融化蒸發作用的冷卻，將改變颱風整體加熱剖面，有可能影響颱風之發展。
此研究結果顯示，納莉颱風的雨帶發展受雲微物理過程影響甚鉅，且氣膠的變化亦對納莉颱風的降水過程與加熱情形有明顯差異，凸顯適切完備的雲微物理過程對於颱風模擬的重要性。

關鍵字

雲凝結核 ； 納莉颱風 ； 對流結構 ； 雲微物理參數法

並列摘要

Many numerical studies have shown that cloud microphysical processes can have significant impact on the track, structure and precipitation of typhoon. However, few studies have investigated the effect of varying cloud condensation nuclei (CCN) concentration on typhoon’s evolution. It is therefore important to understand the role of aerosol during typhoon’s developing phase. To address this issue, Typhoon Nari (2001) is selected for investigation because of its slow translation speed and special track which stays close to the land and aerosol sources for an extended period of time. The WRF model incorporated with a semi-two-moment mixed-phase cloud microphysical scheme which can properly resolve aerosol-cloud microphysical interaction is used to study such effects.
The simulations show that different CCN conditions lead to significant changes in the track, intensity and axisymmetric structure of Nari. Under more polluted aerosol situation, the main rainband becomes more convective and produces wider stratiform region as a result of weakened warm-rain processes and enhanced ice-phase processes. Furthermore, the squall-line-like structure of the rainband becomes more prominent, including a stronger upper-level latent heat release and below cloud evaporation which lead to enhanced rear inflow that brings in mid-level dry air. This leads to a stronger level-cold pool and the invigoration of convective inflow. The differential high-level heating and lower level cooling in the stratiform region of the rainband caused by aerosols may also alter the overall thermal structure and development of this typhoon.

並列關鍵字

Cloud condensation nuclei ； Typhoon Nari ； Convection structure ； Cloud microphysical scheme

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