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

[1] 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.