雙偏極化雷達資料分析梅雨鋒面雨滴粒徑分佈的物理特性

Using dual-polarization radar measurements to analyse the microphysics characteristics of the drop size distribution of Mei-yu frontal rainfall.

呂崇華(Chung-Hua Lu)

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(2006年)

摘要

本研究為利用中央大學C頻雙偏極化(C-Pol)雷達進行台灣地區梅雨鋒面通過期間降水系統特徵之觀測研究。在分析資料前首先建立完整的雷達資料品管流程，利用偏極化雷達參數差異相位差(ΦDP)進行回波( )與差異反射率( )之系統偏移與衰減的修正，以減少反演雨滴粒徑分佈所可能造成的誤差，同時經確認結果證實雷達參數有明顯提升其精確度。
在反演雨滴粒徑分佈及估算降雨率方面，為假設雨滴粒徑為Gamma分佈型態，並利用雨滴粒徑形狀(μ)與斜率(Λ)參數間的經驗關係式以及配合偏極化雷達觀測之回波( )、差異反射率( )及比差異相位差( )資料求得Gamma型態雨滴粒徑分佈三參數。由偏極化雷達反演雨滴粒徑分佈進而求得雲中各物理積分參數，定量上與地面雨滴譜儀觀測有良好的一致性，確認其反演參數之正確性後，將偏極化雷達反演資料應用至梅雨鋒面期間各類降水系統雨滴粒徑分佈特性，以探討其降水系統中雲物理的機制。
由本研究顯示，在二對流個案系統中，相同的高降雨率分別是由雨滴數量（相對多）及雨滴粒徑（相對大）所主導，二個案在雨滴粒徑分佈上有較不同的差異；雨滴碰撞結合及分裂過程，隨降雨率增大最終將會達到平衡，雨滴粒徑大小為一穩定值；此外，研究中也發現在對流及層狀個案中雷達參數相關係數（ ）在冰水混合區會有降低現象。

關鍵字

雨滴粒徑分佈 ； 差異反射率

並列摘要

The major purpose of this research is to understand the microphysics characteristics of Mei-yu frontal system over Taiwan area using NCU C-band dual-polarization (C-Pol) radar measurements. A sequence of quality control procedures are carried out by using the differential phase measurements (ΦDP) to correct the system bias and attenuation of reflectivity (ZH) and differential reflectivity (ZDR). The corrected radar parameters were verified, the improvement after correction procedure is pronounced.
The method for retrieving drop size distribution (DSD) parameters is to assume that the drop size distribution (DSD) is represented by a gamma distribution, and an empirical relation between the distribution shape (μ) and slope (Λ) parameters. Then the three gamma parameters ( 、 、 ) can be derived from the polarimetric variables (ZH、ZDR and KDP) through an forward numerical calculation of scattering model. Retrieved physical characteristics of the drop size distribution (DSD) were generally well matched with disdrometer observations. The retrieval data is applied to the selected Mei-yu frontal precipitation cases to analyze the microphysics characteristics of the rainfall system.
The research results indicate that two strong convective cases are dominated by relatively large drops number and relatively large drops size respectively at the same rainfall rate. Two cases have great variation in the drop size distribution (DSD). At high rain rates, the D0 values reach a steady value what are believed to be equilibrium DSDs in which breakup and accretion are roughly in balance. Besides, the radar measurements suggest that the correlation coefficient (ρhv) in both convective rain and stratiform rain will lower under mixed-phase precipitation.

並列關鍵字

Drop size distribution ； Differential reflectivity

參考文獻

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