Observation of three‐dimensional structures of quasi‐periodic echoes associated with mid‐latitude sporadic‐E layers by MU radar ultra‐multi‐channel system

Abstract

Quasi‐periodic (QP) backscatter observed by VHF radars associated with the mid‐latitude Sporadic‐E (Es) layers is characterized by distinct striations on range‐time‐intensity (RTI) plots. Two competing models claim to explain the structure of unstable regions that scatter the radar waves: horizontally drifting patches at an almost constant altitude and unstable regions elongated in altitude along the geomagnetic field line. We have conducted interferometric imaging observations of QP radar echoes to investigate spatial structures of QP echoes, precisely. Kyoto University's newly developed ultra‐multi‐channel receiving system of middle and upper atmosphere (MU) radar was used. We used 19 independent channels for the radar imaging, and determined the three‐dimensional structure and the motion of the QP echoes. During the observation from 30 May to 02 June 2005, well‐defined QP echoes were observed on the nights of 31 May, 01 June, and 02 June 2005. Some of QP echoes were found at altitudes higher than 120 km and appeared to descend in altitude as they approached the radar. This result suggests that backscatter regions are developed along the geomagnetic field line from Es layer altitudes to as high as 130 km and that the fluctuations in plasma density and electric field observed by Pfaff et al. (2005) using in‐situ measurements form a part of QP echoes.