可預報冰晶成長習性和視密度之多矩量冷雲總體雲微物理參數法應用於WRF模式

A Multi-Moment Bulkwater Ice Microphysics Scheme with Consideration of the Adaptive Growth Habit and Apparent Density for Pristine Ice in the WRF Model

蔡子衿(Tzu-Chin Tsai)

指導教授 ： 陳正平

國立臺灣大學/理學院/大氣科學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.00329

摘要

在雲模式中，冰晶複雜的形狀和其成長機制一直是冷雲參數法裡不易處理的物理過程。而本研究根據Chen and Lamb在1994年所提的冰晶成長理論參數法發展出一套冰晶形狀總體參數法，還建立一個具有六種雙矩量(質量和數量)水物且都是伽碼粒徑分佈的總體雲物理參數法。兩個新的參數法都已移植至WRF氣象模式，成為一個多矩量總體雲微物理參數法。在新的參數法中，更針對雲冰增加了冰晶形狀和體積兩個矩量來預報其成長習性和視密度，並提出一個使用第零、第二和第三矩量之矩量閉合方法。而冰晶形狀總體參數法的理論驗證是和細格(bin)方法作比較；氣塊(parcel)法零維計算的結果展示出粒徑譜形能彈性變化的重要性，以及冰晶形狀對其凝華成長的顯著影響，同時冰晶的成長習性能夠根據不同的環境條件及初始粒徑做出調整；總體三矩量方法和細格方法的結果較為一致。至於觀測驗證，分別選取C3VP和DIAMET兩個冬季觀測計畫之個案以WRF模式進行模擬，並分別假設球形和非球形的冰晶來評估其影響程度。C3VP個案模擬結果顯示出雲冰形狀在雲物理過程、地面降水和輻射通量的顯著影響及較為接近真實的冰晶成長習性演變。而DIAMET個案結果顯示，新的雲微物理參數法能準確地預報其鋒面狹長雨帶的降水結構和伴隨的天氣特徵，且模擬出柱狀和碟狀冰晶在不同溫度區間的垂直分布並記憶其形狀的演變，而和飛機雲物理觀測資料的比較亦顯示冰晶在其二次增殖生成的溫度區間，兩者在冰晶數量濃度、綜橫軸比例和其凝華加熱率具有高度的一致性。

關鍵字

冰晶形狀 ； 冰晶習性 ； WRF ； 雲物理參數法 ； C3VP ； DIAMET

並列摘要

The wide variety of ice crystal shapes and growth habits makes it a complicated issue in cloud models. This study developed the bulk ice adaptive habit parameterization based on the theoretical approach of Chen and Lamb (1994) and introduced a 6-class hydrometeors double-moment (mass and number) bulk microphysics scheme with gamma-type size distribution function. Both the proposed schemes have been implemented into the Weather Research and Forecasting model (WRF) model forming a new multi-moment bulk microphysics scheme. Two new moments of ice crystal shape and volume are included for tracking pristine ice’s adaptive habit and apparent density. A closure technique is developed to solve the time evolution of the bulk moments. For the verification of the bulk ice habit parameterization, some parcel-type (zero-dimension) calculations were conducted and compared with binned numerical calculations. The results showed that: a flexible size spectrum is important in numerical accuracy, the ice shape can significantly enhance the diffusional growth, and it is important to consider the memory of growth habit (adaptive growth) under varying environmental conditions. Also, the derived results with the 3-moment method were much closer to the binned calculations. Two field campaigns from the C3VP and DIAMET were selected to simulate in the WRF model for real-case studies. The simulations were performed with the traditional spherical ice and the new adaptive shape schemes to evaluate the effect of crystal habits. Realistic evolution of ice growth habits and great impacts on the ice-phase microphysical processes, surface precipitations, and radiation fluxes were found in the simulation results of C3VP case. For the DIAMET case, some main features of narrow rain band, as well as the embedded precipitation cells, in the cold front case were well captured by the model. The vertical variation of ice crystal shapes was nicely simulated. Furthermore, the simulations produced a good agreement in the microphysics against the aircraft observations in ice particle number concentration, ice crystal aspect ratio, and deposition heating rate especially within the temperature region of ice secondary multiplication production.

並列關鍵字

crystal shape ； ice habit ； WRF ； cloud scheme ； C3VP ； DIAMET

參考文獻

Avramov, A., and J. Y. Harrington, 2010: Influence of parameterized ice habit on simulated mixed phase Arctic clouds, J. Geophys. Res., 115, D03205.

Baumgardner, D., H. Jonsson, W. Dawson, D. O’Connor, and R. Newton, 2001: The cloud, aerosol and precipitation spectrometer: a new instrument for cloud investigations, Atmos. Res., 59, 251–264.

Bailey, M.P., and J. Hallett, 2009: A comprehensive habit diagram for atmospheric ice crystals: confirmation from the laboratory, AIRS II, and other field studies, J. Atmos. Sci., 66, 2888–2899.

Beard, K. V., and H. R. Pruppacher, 1971: A wind tunnel investigation of the rate of evaporation of small water drops falling at terminal velocity in air. J. Atmos. Sci., 28, 1455–1464.

Bigg, E. K., 1953: The supercooling of water. Proc. Phys. Soc. London., B66, 688–694.