在降水環境下，特高頻雷達回波機制源自於雷萊散射(Rayleigh Scattering)，以降水粒子為目標物，當雷達發射電磁波波長遠大於所觀測降水粒子的尺度時，電磁波入射降水粒子時，降水粒子所感應電場強度幾乎相同，降水粒子將散射電磁波。故降水粒子粒徑將直接影響雷達回波訊號，例如回波的都卜勒速度、頻寬或回波強度等。另外，雨滴譜儀可了解降水粒子在空中的粒徑分布狀況，故可利用雨滴譜儀掌握降水粒子在大氣中的時序變化。本研究計畫將使用中壢特高頻雷達，配合地面雨滴譜儀，觀測大氣降水環境，研究大氣降水粒子的一些重要參數。經由雨滴譜儀所量測到雨滴粒徑的分布，使用指數函數(exponential function)做湊配。以這個基本性質，配合雨滴下墜速度與粒徑間的power‐law關係，導出特高頻雷達觀測到降水粒子終端速度與回波功率經距離修正後，兩者間的理論關係。並探討降水粒子粒徑分布，對雷達回波的影響。另外，指數形式分布α=Aexp(‐ξβ)，A是V=ADB的係數，D是雨滴粒徑，ξ是雷達參數與降水強度的因子。從雷達觀測中找到β與雷達晴空回波大氣垂直速度的相關性。 ; The mechanism of the VHF radar echo returns under precipitation can be derived from the principle of Rayleigh Scattering. When the radar wavelength of the incident electromagnetic wave is much greater than the size of the precipitation particles, the induced electric field will be almost the same as that of the incident wave. The electromagnetic wave can be scattered back to the radar.and the physical size of the precipitation particle contributes to Doppler velocity, signal bandwidth and echo power, etc. of the radar echoes. In addition, Size distribution of the precipitation particles in the air can be deduced from the 2‐D Disdrometer observation. We can understand the sequential variation of the precipitation from data collected by Disdrometer. The purpose of this project is to study some important parameters through VHF radar observation and data collected with 2D Disdrometer. The disribution of rain drop size from Disdrometer can be curve fitted with exponential funtion. Combine this basic relation with the power‐law derived from rain drop size and its terminal velocity, the theoretical relation between terminal velocity and echo power of the precipitation particle can be deduced wth range correction. The impact on the radar echo by the particle size distribution will be discussed during this project. The mathematical relationship between α and β is indeed in an exponential form, namly, α=Aexp(‐ξβ), where A is the coefficient in the relation V=ADB, D is the diameter of the rain drop, and ξ is a factor related to radar parameters and precipitation intensity. From the observational results made with the Chung‐Li VHF radar, find the relationship between the value of β and the vertical air velocity. ; 研究期間 9708 ~ 9807
