Mesosphere summer echoes observed with the SuperDARN Hokkaido HF radar at Rikubetsu, Japan (43.5°N)

Using the SuperDARN Hokkaido HF radar located at Rikubetsu in Hokkaido, Japan (43.5°N), we present first oblique-incidence observations of midlatitude mesosphere summer echoes (MSE) at the HF band (HF-MSE). Three HF-MSE events in June 2009 are case-studied. Analyses of HF-MSE data together with VHF and MF radar data obtained at Wakkanai, 260 km northwest of Rikubetsu, indicate the following: (1) in two events HF-MSE were accompanied by MSE at VHF (VHF-MSE), and in one event only HF-MSE were observed. (2) In accordance with southward neutral winds observed with the MF radar, HF-MSE exhibited high Doppler velocities with a maximum of about 60 m/s toward the south, and also HF-MSE regions moved southward with time, suggesting that irregularities and/or cold ice particles responsible for the radar wave scattering might be advected southward from higher latitudes.