Quasi-periodic echoes observed with the Chung-Li VHF radar during the SEEK campaign

The 52-MHz Chung-Li VHF radar, located in Taiwan, was operated during the SEEK (Sporadic-E Experiment over Kyushu) campaign to investigate the so-called quasi-periodic (QP) echoes that occur from nighttime sporadic E (E_s) layers. Highlights of this study are presented in this paper, using measurements made on August 17, 1996, to illustrate the echo characteristics. QP echoes displaying 5 to 10 minute periods were observed throughout this night. A new finding is the occurrence of QP echoes whose striations were almost vertically oriented when plotted using a height-time-intensity (HTI) format. This observation provides the first unambiguous evidence for the existence of steep spatial tilts in E_s layers that are responsible for QP echoes. Other characteristics from three periods during this night are described including striations with positively sloped striations. These characteristics are discussed in light of existing models for QP echoes.