Simultaneous observations of nighttime medium‐scale traveling ionospheric disturbances and E region field‐aligned irregularities at midlatitude

We report on simultaneous observations of very high frequency (VHF) radar backscatter from field‐aligned irregularities (FAI) in the E region and medium‐scale traveling ionospheric disturbances (MSTID) in 630‐nm airglow images. On the night of 6 August 2002, the powerful 46.5‐MHz middle and upper atmosphere (MU) radar with five beam directions at Shigaraki, Japan, observed typical quasiperiodic (QP) echoes from FAI in the E region. During this QP echo event, an all‐sky charge‐coupled device imager at the MU radar site detected MSTID in 630‐nm airglow images. The MSTID also propagated southwestward at 80 m/s with fluctuation amplitudes of 50% from the background intensity and a wavelength of 380 km. Period of the MSTID was almost same as that of the Doppler velocity in the QP echoes. The airglow enhancement (depletion) caused by the MSTID coincided with southeastward (northwestward) velocity in the QP echo. These results indicate that the electric fields associated with the F region MSTID could be closely coupled to those associated with QP echoes in the E region.