雨滴粒徑分布模擬─雙偏極化雷達驗證

Simulation of Raindrop Size Distribution:Verification using the Dual-polarization Radar

曾威仁(Wei-ren Tseng)

指導教授 ： 陳台琦

國立中央大學/地球科學學院/大氣物理研究所/碩士(2007年)

摘要

大學雙偏極化雷達反演空中雨滴粒徑分布之技術，模擬台灣山區夏季午後天氣系統中，層狀區與對流區之雨滴粒徑分布的演化過程，並以雷達觀測產品作為驗證。
研究結果發現，在沒有考慮水平方向空氣平流的情況下，透過給予一組層狀區上空3.5公里處的雨滴粒徑分布，一維雲模式能夠順利掌握到該區域的中值體積直徑向下逐漸增加、高低層差值隨時間逐漸減小的趨勢。此外模擬9至10分鐘後其模擬之垂直分布即相當接近雷達的反演場。強度逐漸減弱的對流區，模式計算出來的中值體積直徑在離地3.5至2.5公里的1公里內有減小的趨勢、在2.5公里以下則維持平衡的狀況不再變化。而雷達反演的中值體積直徑在3.5公里以下則是一直保持定值。推論主要的原因包含對流區可能存在本實驗並未內入模式計算的空氣平流運動；並且不論是雷達反演雨滴粒徑分布、或者一維雲模式均以無冰相粒子的暖雨過程作為前提，倘若該區域為冰水混相的狀態，則需要經由濾除冰粒子的數量方能有效進行應用。

關鍵字

雲模式 ； 雷達 ； 雨滴粒徑分布

並列摘要

Along the long history of the microphysical model development, the distrometer is one of the main tools to verify the evolution of the raindrop size distribution from the model calculation. In this research, the advantages of the dual-polarization radar, such as, the greater spatial and temporal resolution, and the ability of retrieving the raindrop size distribution using the reflectivity (ZH) , differential reflectivity (ZDR), and a given μ - Λ relationship in the gamma form distribution. So, the major purpose of this research is to use radar data to confirm the output of the one dimensional cloud model during the real case. In order to understand the characteristics in both the stratiform and convective zones of a summer thunderstorm in North Taiwan, the raindrop size distribution in both regions were carefully retrieved from the dual-polarization radar data.
There are distinct results in the stratiform and convective zones. In the stratiform zone, the median volume diameter (D0) retrieved from the NCU radar is increasing downward. Although lacking the advection information in the model, the outputs agree well with the observation data. In the convective zone, the median volume diameter computed from the model is decreasing at first 1 km decent and then near constant along the rest of the fall. The radar retrieval were also near constant below 3.5 km however. The possible explanations are the existence of ice or supercooled water in the convective area; it causes the error in both radar retrieval and model calculations because of the default warm rain assumption.

並列關鍵字

cloud model ； bin model ； raindrop size distribution ； radar ； DSD

參考文獻

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