QUASI-PERIODIC ECHOES OBSERVED WITH THE CHUNG-LI VHF RADAR DURING THESEEK CAMPAIGN

The 52-MHz Chung-Li VHF radar, located in Taiwan, was operated during the SEEK (Sporadic-E Experiment over Kyushu) campaign to investigate t he so-called quasi-periodic (QP) echoes that occur from nighttime spor adic E (E-s) layers. Highlights of this study are presented in this pa per, using measurements made on August 17, 1996, to illustrate the ech o characteristics. QP echoes displaying 5 to 10 minute periods were ob served throughout this night. A new finding is the occurrence of QP ec hoes whose striations were almost vertically oriented when plotted usi ng a height-time-intensity (HTI) format. This observation provides the first unambiguous evidence for the existence of steep spatial tilts i n E-s layers that are responsible for QP echoes. Other characteristics from three periods during this night are described including striatio ns with positively sloped striations. These characteristics are discus sed in light of existing models for QP echoes.