Observations of QP radar echo structure consistent with neutral wind shear control of the initiation mechanism

The semidiurnal variations in quasi-periodic echo structure parameters associated with midlatitude sporadic E layers observed with the Chung-Li VHF radar located in Taiwan (24.9 N, 121.2 E; 52 MHz) are presented. The results show that the periodicity decreases with increasing range rate and that the spread of Doppler velocities increases as the altitude coverage of the echoes increases. These 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.