HF radar observations of quasiperiodic E layer echoes over North America

Midlatitude E region plasma irregularities have been observed with a new, low-power HF coherent scatter radar at Clemson, South Carolina. The observations reveal a high incidence of quasiperiodic striations like those first observed at the Middle and Upper Atmosphere (MU) radar in Shigaraki, Japan. Quasiperiodic echoes were seen on approximately 70% of the evenings in August 1998 on which observations were made. They occurred mainly at altitudes above 100 km, had range rates usually between -100 and -150 m/s, implying propagation toward the radar (downward and southward), but typically exhibited Doppler velocities indicating rapid phase propagation away from the radar (upward and northward). The quasiperiodic echoes sometimes had periods comparable to the Brunt-Vaisala period but more often had significantly shorter periods, closer to 1 min. The Doppler shifts of the strongest echoes oscillated with a period of just under 1 hour, and the phase of this oscillation seemed to control the occurrence of the radar echoes.