本研究以一詳盡雲微物理模式探討對台灣北部冬季地形雲施行暖雲種雲的可能性。首先分析自然狀態下氣懸粒子粒徑分佈的重要性,結果顯示不同粒徑分佈型態會造成雲微物理結構的顯著差異,尤其是巨核粒子,其大小與數量控制著暖雲的降水效率。以親水性凝結核種雲的數值實驗結果顯示,種雲效果也會隨氣懸粒子分佈型態而異:原本降水效率較差的大陸型情景可得到較佳的種雲效果;原本降水效率較高的海洋型與陽明山型情景則種雲效果較差,甚至可呈現負面效果。同時,種雲核播放的位置對造雨量和降水時機都有很大的影響。種雲效果也與種雲核的粒徑與數量濃度有關,最佳數量濃度約為10 cm^(-3),最佳粒徑分佈則為10 μm左右。對種雲成本效益之概略評估所得結果如下:大陸型、海洋型、陽明山型情景的最高益本比各可達20倍、13倍、4倍左右。這些初步結果顯示,台灣北部冬季的地形雲具有種雲的潛在價值,值得進一步的研究。
A detailed microphysics model is applied to study the feasibility of warm-cloud seeding in wintertime orographic clouds over northern Taiwan. Simulations are first performed to analyze the effect of aerosol particles on undisturbed clouds, showing that the difference in aerosol size distribution can significantly impact the microphysics structures of clouds. In particular, the presence of giant nuclei is crucial to the development of precipitation. The effect of seeding with hygroscope material is shown to vary with the pattern of natural aerosol size distributions. The situations with continental type aerosols and lower precipitation rates tend to have better seeding results, whereas those with maritime type or Mt. Yang-Ming type aerosol tend to have inferior or even negative results. Tests on the seeding techniques indicate that the locations of seeding not only influence the magnitude of precipitation enhancement but also its timing. Optimal values for the number concentration and size of seeding nuclei are found to be 10 cm^(-3) and 10~30 μm, respectively. Estimations on the optimum benefit-to-cost ratios of seeding for the continental, maritime and Mt. Yang-Ming type situations are roughly 20, 13, and 4 times, respectively. These preliminary results indicate that seeding operation in the wintertime orographic clouds over northern Taiwan seem to be feasible, which warrants more extensive future studies.
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