以雙矩量雲微物理機制探討雲凝結核對極端降水之影響:西南氣流實驗個案分析

本研究以CLR雙矩量雲微物理機制在區域模式中對2008年西南氣流實驗第八次密集觀測（SoWMEX/TiMREX IOP8）台灣海峽地區中尺度對流系統個案進行區域模式模擬，以S-波段雙偏極都卜勒氣象雷達(S-Pol radar)及撞擊式雨滴譜儀(JWD)觀測資料對回波機率分布、雨滴粒徑分布、降雨強度譜及時空分布等結果進行評估，並與Morrison雙矩量雲微物理機制的模擬結果比較。接著利用CLR機制來探討不同雲凝結核背景濃度對雲微物理及中尺度對流的影響，觀察模擬的系統中對流區與層狀區對雲凝結核變化的敏感性。結果顯示CLR機制的模擬中各個高度皆模擬出較觀測資料大的最大雷達回波及最大頻率的雷達回波，較強的對流上升速度、較弱的對流下沉速度及較小的地表的雨滴大小。雲凝結核數量多的CLR-continental模擬出較CLR-maritime少的雨滴、較多的雲滴。CLR-continental模擬出了較CLR-maritime強的上升氣流，推測是由於CLR-continental模擬出較多由雲滴凝結成長所釋放的潛熱，進而影響模擬的對流強度。增加氣膠在對流區及層狀區中都會使水物的質量濃度上升，其中以雪的增加最為顯著。在對流區中氣膠較多的環境模擬出了較集中的降水。延續前述推測CLR-continental模擬出較強上升氣流的原因，發現氣膠多寡所造成由雲滴凝結成長所釋放潛熱的差異主要來自於對流區。本研究指出，探討對流系統受氣膠濃度的影響時，除了分析平均狀態，也應分析系統細部的結構變化及極端降水與上升速度的改變。後續的研究將針對混相微物理過程所造成的潛熱變化及近地表冷池與垂直風切的交互作用對背景氣膠種類的反應進行探討。

關鍵字

雲微物理機制；氣膠；中尺度對流系統；雨滴粒徑；降水強度

並列摘要

This study simulates a mesoscale convective system during SoWMEX/TiMREX IOP8 by the Chen-Liu-Reisner (CLR) physical-statisical two-moment bulk microphysics scheme in the Weather Research and Forecast regional model. The results are evaluated against the observations and retrievals from the S-Pol radar and disdrometer, including the reflectivity probability distribution, rain drop size, precipitation intensity spectrum. Comparison with the simulation using the Morrison two-moment bulk microphysics scheme is also carried out. The CLR scheme is then applied to investigate the impact of different CCN types on the extreme upraft and precipitation. The CLR scheme simulates higher maximum radar reflectivity and higher peak probability radar reflectivity than observations at all altitude. Stronger updrafts, weaker downdrafts and smaller size of rain drops at the surface than observations are simulated by the CLR scheme. The CLR-continental (polluted) scheme simulates stronger updrafts in the convective areas than the CLR-maritime (clean) scheme does, owing to the reason that more latent heat is generated by cloud drop diffusional growth, thereby enhancing the intensity of the convection in the CLR-continental simulation. This study illustrates that, to identify the impacts of aerosols on convective system, it is imperative to analyze the responses in detailed storm structure, extreme precipitation, and extreme vertical velocity in addition to the analyses of the mean state changes. Future work will focus on investigating the response of latent heating rate by various mixed-phase microphysics processes and the interactions between surface cold pool and the vertical wind shear to different background CCN types.

並列關鍵字

microphysics scheme ； aerosols ； mesoscale convective system ； rain drop size ； precipitation intensity

參考文獻

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Chen, J.-P., and D. Lamb, 1994: Simulation of Cloud Microphysical and Chemical Processes Using a Multicomponent Framework. Part I: Description of the Microphysical Model. J. Atmos. Sci., 51, 2613–2630, doi:10.1175/1520-0469(1994)051<2613:SOCMAC>2.0.CO;2.

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——, and S.-T. Liu, 2004: Physically based two-moment bulkwater parametrization for warm-cloud microphysics. Q. J. R. Meteorol. Soc., 130, 51–78, doi:10.1256/qj.03.41. http://dx.doi.org/10.1256/qj.03.41.

Cheng, C.-T., W.-C. Wang, and J.-P. Chen, 2010: Simulation of the effects of increasing cloud condensation nuclei on mixed-phase clouds and precipitation of a front system. Atmos. Res., 96, 461–476, doi:10.1016/j.atmosres.2010.02.005. http://dx.doi.org/10.1016/j.atmosres.2010.02.005.

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以雙矩量雲微物理機制探討雲凝結核對極端降水之影響:西南氣流實驗個案分析

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