由於近年來雷達觀測的結果，已經成功的證明了赤道(equator)和中緯度(mid-laitutde)地區的E層不規則體(irregularities)的存在。 而在赤道地區的不規則體的回波都為連續性回波(continuous radar echoes)這種回波不論是白天或晚上都有出現，且其不規則體的型態為型態１(type I)以及型態2(type II)兩種。早期在中緯度地區，由於雷達技術較不為發達，雖然有觀測到不同於連續性回波的雷達回波(即所謂的準週期性雷達回波，quasi-periodic radar echoes)，亦在RTI(range-time-intensity plot)圖上發現到這種回波有一2~15分鐘的出現週期，但是當時所用來觀測的雷達，其空間解析度均只有3~15公里。一直到日本的MU雷達的加入以後(空間解析度為600公尺)，才可以開始對種種的雷達回波做更進一步的研究。Yamamoto et al.,(1991)便是首位利用MU達觀測到準週期性回波的學者。這一類的回波在RTI圖上是間歇性的出現，而非連續性。而本論文之研究主要則是在於利用中壢VHf雷達對電離層散塊E層觀測實在RTI圖上所出現的準週期性回波做一進一步的分析與研究，並將在中壢所觀測道的準週期性回波與其他雷達所觀測到的準週期性回波做一比較與整理。 The main purpose of this thesis is to do the research about the quasi-periodic radar echoes detected by Chung-Li VHF radar and Gadanki MST radar from radial Doppler velocity, range rate, periodicity, and spectral width. The results show that the periodicity decreases with increasing range rate and the direction of the radial Doppler velocity in the upper and the lower region of some QP striations detected by Gadanki MST radar are opposite. Besides these two characteristics, we also find that the spread of Doppler velocities increases as the altitude coverage of the echoes increases. These three characteristics are shown to be consistent with the variations to be expected if the shears in the neutral wind and the variations in the background mean flow are the dominant mechanisms controlling the initiation of the echo structures. Moreover, there are seven radar stations detect the phenomenon of QP echoes from 1991 to 1999,so we also compare the observation results between these seven different radars located in different latitude .
